Set V - Seasonal 7-month forecast (SEAS)

Configure and order Set V

SEAS comprises ensembles of individual forecasts coupled to an ocean model and post-processed products of average conditions (e.g. monthly averages) with the associated uncertainty. Products are available up to 7 months ahead.

The following sub-sets are available:

V-i: Monthly means of ensemble means

Field computed from data of the daily individual forecast runs (section V-v) and averaged over all ensemble members. The fields are provided in GRIB code.

V-ii: Monthly mean anomalies of ensemble means

V-iii: Monthly means of individual ensemble members

V-iv: Monthly mean anomalies of individual ensemble members

V-v: Individual forecast runs

Definition of the monthly fields

The definition of the month is in accordance to the calendar month of the western calendar

  • Monthly means are computed using values at write-up times 00, 06, 12 and 18 UTC for
    • 2m temperature (K)
    • 10m U-velocity (m/s)
    • 10m V-velocity (m/s)
    • MSLP (Pa)
  • Monthly means are computed using values at write-up times 00 and 12 UTC for
    • Pressure-level parameters
  • Monthly means are computed using values at the write-up time 00 for
    • Sea surface temperature (K)
    • Soil temperature level 1 (K)
    • Volumetric soil water layer 1 (m**3 m**-3)
  • Monthly mean total precipitation (m/s) is the rate of precipitation during the month.
  • Maximum temperature at 2 meters (K) is the monthly mean of the maximum of MX2T (Maximum temperature at 2 meter since last post-processing).
  • Minimum temperature at 2 meters (K) is the monthly mean of the minimum of MN2T (Minimum temperature at 2 meters since last post-processing).

Dissemination schedule

(dissemination data stream indicator = L) 

Forecast time Time available
Forecast month 1-7 5th of each month 12:00 UTC

V-i: Monthly means of ensemble means

Forecast ranges & resolution

Ranges Base times Resolution
1 to 7 month 00 UTC
  • 0.4° x 0.4° lat/long grid or any multiple thereof (global or sub-area)
  • 0.75° x 0.75° lat/long grid or any multiple thereof (global or sub-area)
  • On model (Gaussian) O320 (35 km) grid (global or sub-area)
  • Spectral components (T319) for upper-air fields (global area only)

 V-i-a: Single level 

Short Name ID Long Name Description Units Additional information
ci 31 Sea ice area fraction This parameter is the fraction of a grid box which is covered by sea ice. Sea ice can only occur in a grid box which includes ocean or inland water according to the land sea mask and lake cover, at the resolution being used. This parameter can be known as sea-ice (area) fraction, sea-ice concentration and more generally as sea-ice cover.

Coupled atmosphere ocean simulations of the ECMWF Integrated Forecasting System (IFS) predict the formation and melting of sea ice. Otherwise, in analyses and atmosphere only simulations, sea ice is derived from observations, but the model does take account of the way that sea ice alters the interaction between the atmosphere and ocean.

Sea ice is frozen sea water which floats on the surface of the ocean. Sea ice does not include ice which forms on land such as glaciers, icebergs and ice-sheets. It also excludes ice shelves which are anchored on land, but protrude out over the surface of the ocean. These phenomena are not modelled by the IFS.

Long-term monitoring of sea ice is important for understanding climate change. Sea ice also affects shipping routes through the polar regions.
(0 - 1)  
rsn 33 Snow density This parameter is the mass of snow per cubic metre in the snow layer.

The ECMWF Integrated Forecast System (IFS) model represents snow as a single additional layer over the uppermost soil level. The snow may cover all or part of the grid box.

See further information on snow in the IFS.
kg m**-3  
sst 34 Sea surface temperature This parameter is the temperature of sea water near the surface.

This parameter is taken from various providers, who process the observational data in different ways. Each provider uses data from several different observational sources. For example, satellites measure sea surface temperature (SST) in a layer a few microns thick in the uppermost mm of the ocean, drifting buoys measure SST at a depth of about 0.2-1.5m, whereas ships sample sea water down to about 10m, while the vessel is underway. Deeper measurements are not affected by changes that occur during a day, due to the rising and setting of the Sun (diurnal variations).

Sometimes this parameter is taken from a forecast made by coupling the NEMO ocean model to the ECMWF Integrated Forecasting System. In this case, the SST is the average temperature of the uppermost metre of the ocean and does exhibit diurnal variations.

See further documentation .

This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.
K  
swvl1 39 Volumetric soil water layer 1 This parameter is the volume of water in soil layer 1 (0 - 7cm, the surface is at 0cm).

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:
Layer 1: 0 - 7cm
Layer 2: 7 - 28cm
Layer 3: 28 - 100cm
Layer 4: 100 - 289cm

The volumetric soil water is associated with the soil texture (or classification), soil depth, and the underlying groundwater level.
m**3 m**-3  
swvl2 40 Volumetric soil water layer 2 This parameter is the volume of water in soil layer 2 (7 - 28cm, the surface is at 0cm).

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:
Layer 1: 0 - 7cm
Layer 2: 7 - 28cm
Layer 3: 28 - 100cm
Layer 4: 100 - 289cm

The volumetric soil water is associated with the soil texture (or classification), soil depth, and the underlying groundwater level.
m**3 m**-3  
swvl3 41 Volumetric soil water layer 3 This parameter is the volume of water in soil layer 3 (28 - 100cm, the surface is at 0cm).

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:
Layer 1: 0 - 7cm
Layer 2: 7 - 28cm
Layer 3: 28 - 100cm
Layer 4: 100 - 289cm

The volumetric soil water is associated with the soil texture (or classification), soil depth, and the underlying groundwater level.
m**3 m**-3  
swvl4 42 Volumetric soil water layer 4 This parameter is the volume of water in soil layer 4 (100 - 289cm, the surface is at 0cm).

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:
Layer 1: 0 - 7cm
Layer 2: 7 - 28cm
Layer 3: 28 - 100cm
Layer 4: 100 - 289cm

The volumetric soil water is associated with the soil texture (or classification), soil depth, and the underlying groundwater level.
m**3 m**-3  
mx2t24 51 Maximum temperature at 2 metres in the last 24 hours The highest value of 2 metre temperature in the previous 24 hour period.

2m temperature is calculated by interpolating between the lowest model level and the Earth's surface, taking account of the atmospheric conditions. See further information.

This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.
K  
mn2t24 52 Minimum temperature at 2 metres in the last 24 hours The lowest value of 2 metre temperature in the previous 24 hour period.

2m temperature is calculated by interpolating between the lowest model level and the Earth's surface, taking account of the atmospheric conditions. See further information.

This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.
K  
tclw 78 Total column cloud liquid water This parameter is the amount of liquid water contained within cloud droplets in a column extending from the surface of the Earth to the top of the atmosphere. Rain water droplets, which are much larger in size (and mass), are not included in this parameter.

This parameter represents the area averaged value for a model grid box.

Clouds contain a continuum of different- sized water droplets and ice particles. The ECMWF Integrated Forecasting System (IFS) cloud scheme simplifies this to represent a number of discrete cloud droplets/particles including: cloud water droplets, raindrops, ice crystals and snow (aggregated ice crystals). The processes of droplet formation, phase transition and aggregation are also highly simplified in the IFS.
kg m**-2  
tciw 79 Total column cloud ice water This parameter is the amount of ice contained within clouds in a column extending from the surface of the Earth to the top of the atmosphere. Snow (aggregated ice crystals) is not included in this parameter.

This parameter represents the area averaged value for a model grid box.

Clouds contain a continuum of different- sized water droplets and ice particles. The ECMWF Integrated Forecasting System (IFS) cloud scheme simplifies this to represent a number of discrete cloud droplets/particles including: cloud water droplets, raindrops, ice crystals and snow (aggregated ice crystals). The processes of droplet formation, phase transition and aggregation are also highly simplified in the IFS.
kg m**-2  
z 129 Geopotential This parameter is the gravitational potential energy of a unit mass, at a particular location, relative to mean sea level. It is also the amount of work that would have to be done, against the force of gravity, to lift a unit mass to that location from mean sea level.

The geopotential height can be calculated by dividing the geopotential by the Earth's gravitational acceleration, g (=9.80665 m s-2). The geopotential height plays an important role in synoptic meteorology (analysis of weather patterns). Charts of geopotential height plotted at constant pressure levels (e.g., 300, 500 or 850 hPa) can be used to identify weather systems such as cyclones, anticyclones, troughs and ridges.

At the surface of the Earth, this parameter shows the variations in geopotential (height) of the surface, and is often referred to as the orography.
m**2 s**-2  
tcwv 137 Total column water vapour This parameter is the total amount of water vapour in a column extending from the surface of the Earth to the top of the atmosphere.

This parameter represents the area averaged value for a grid box.
kg m**-2  
stl1 139 Soil temperature level 1 This parameter is the temperature of the soil at level 1 (in the middle of layer 1).

The ECMWF Integrated Forecasting System (IFS) has a four-layer representation of soil, where the surface is at 0cm:

Layer 1: 0 - 7cm
Layer 2: 7 - 28cm
Layer 3: 28 - 100cm
Layer 4: 100 - 289cm

Soil temperature is set at the middle of each layer, and heat transfer is calculated at the interfaces between them. It is assumed that there is no heat transfer out of the bottom of the lowest layer.

This parameter has units of Kelvin (K). Temperature measured in Kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

See further information.
K  
sd 141 Snow depth This parameter is the depth of snow from the snow-covered area of a grid box.

Its units are metres of water equivalent, so it is the depth the water would have if the snow melted and was spread evenly over the whole grid box. The ECMWF Integrated Forecast System represents snow as a single additional layer over the uppermost soil level. The snow may cover all or part of the grid box.

See further information.
m of water equivalent  
msl 151 Mean sea level pressure This parameter is the pressure (force per unit area) of the atmosphere adjusted to the height of mean sea level.

It is a measure of the weight that all the air in a column vertically above the area of Earth's surface would have at that point, if the point were located at the mean sea level. It is calculated over all surfaces - land, sea and in-land water.

Maps of mean sea level pressure are used to identify the locations of low and high pressure systems, often referred to as cyclones and anticyclones. Contours of mean sea level pressure also indicate the strength of the wind. Tightly packed contours show stronger winds.

The units of this parameter are pascals (Pa). Mean sea level pressure is often measured in hPa and sometimes is presented in the old units of millibars, mb (1 hPa = 1 mb = 100 Pa).
Pa  
tcc 164 Total cloud cover This parameter is the proportion of a grid box covered by cloud. Total cloud cover is a single level field calculated from the cloud occurring at different model levels through the atmosphere. Assumptions are made about the degree of overlap/randomness between clouds at different heights.

Cloud fractions vary from 0 to 1.
(0 - 1)  
10u 165 10 metre U wind component This parameter is the eastward component of the 10m wind. It is the horizontal speed of air moving towards the east, at a height of ten metres above the surface of the Earth, in metres per second.

Care should be taken when comparing this parameter with observations, because wind observations vary on small space and time scales and are affected by the local terrain, vegetation and buildings that are represented only on average in the ECMWF Integrated Forecasting System.

This parameter can be combined with the V component of 10m wind to give the speed and direction of the horizontal 10m wind.
m s**-1  
10v 166 10 metre V wind component This parameter is the northward component of the 10m wind. It is the horizontal speed of air moving towards the north, at a height of ten metres above the surface of the Earth, in metres per second.

Care should be taken when comparing this parameter with observations, because wind observations vary on small space and time scales and are affected by the local terrain, vegetation and buildings that are represented only on average in the ECMWF Integrated Forecasting System.

This parameter can be combined with the U component of 10m wind to give the speed and direction of the horizontal 10m wind.
m s**-1  
2t 167 2 metre temperature This parameter is the temperature of air at 2m above the surface of land, sea or in-land waters.

2m temperature is calculated by interpolating between the lowest model level and the Earth's surface, taking account of the atmospheric conditions. See further information .

This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.
K  
2d 168 2 metre dewpoint temperature This parameter is the temperature to which the air, at 2 metres above the surface of the Earth, would have to be cooled for saturation to occur.

It is a measure of the humidity of the air. Combined with temperature and pressure, it can be used to calculate the relative humidity.

2m dew point temperature is calculated by interpolating between the lowest model level and the Earth's surface, taking account of the atmospheric conditions. See further information.This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.
K  
stl2 170 Soil temperature level 2 This parameter is the temperature of the soil at level 2 (in the middle of layer 2).

The ECMWF Integrated Forecasting System (IFS) has a four-layer representation of soil, where the surface is at 0cm:

Layer 1: 0 - 7cm
Layer 2: 7 - 28cm
Layer 3: 28 - 100cm
Layer 4: 100 - 289cm

Soil temperature is set at the middle of each layer, and heat transfer is calculated at the interfaces between them. It is assumed that there is no heat transfer out of the bottom of the lowest layer.

This parameter has units of Kelvin (K). Temperature measured in Kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

See further information.
K  
lsm 172 Land-sea mask This parameter is the proportion of land, as opposed to ocean or inland waters (lakes, reservoirs, rivers and coastal waters), in a grid box.
This parameter has values ranging between zero and one and is dimensionless.
In cycles of the ECMWF Integrated Forecasting System (IFS) from CY41R1 (introduced in May 2015) onwards, grid boxes where this parameter has a value above 0.5 can be comprised of a mixture of land and inland water but not ocean. Grid boxes with a value of 0.5 and below can only be comprised of a water surface. In the latter case, the lake cover is used to determine how much of the water surface is ocean or inland water.
In cycles of the IFS before CY41R1, grid boxes where this parameter has a value above 0.5 can only be comprised of land and those grid boxes with a value of 0.5 and below can only be comprised of ocean. In these older model cycles, there is no differentiation between ocean and inland water.
(0 - 1)  
stl3 183 Soil temperature level 3 This parameter is the temperature of the soil at level 3 (in the middle of layer 3).

The ECMWF Integrated Forecasting System (IFS) has a four-layer representation of soil, where the surface is at 0cm:

Layer 1: 0 - 7cm
Layer 2: 7 - 28cm
Layer 3: 28 - 100cm
Layer 4: 100 - 289cm

Soil temperature is set at the middle of each layer, and heat transfer is calculated at the interfaces between them. It is assumed that there is no heat transfer out of the bottom of the lowest layer.

This parameter has units of Kelvin (K). Temperature measured in Kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

See further information.
K  
lcc 186 Low cloud cover This parameter is the proportion of a grid box covered by cloud occurring in the lower levels of the troposphere. Low cloud is a single level field calculated from cloud occurring on model levels with a pressure greater than 0.8 times the surface pressure. So, if the surface pressure is 1000 hPa (hectopascal), low cloud would be calculated using levels with a pressure greater than 800 hPa (below approximately 2km (assuming a 'standard atmosphere')).

The low cloud cover parameter is calculated from cloud cover for the appropriate model levels as described above. Assumptions are made about the degree of overlap/randomness between clouds in different model levels.

Cloud fractions vary from 0 to 1.
(0 - 1)  
tco3 206 Total column ozone This parameter is the total amount of ozone in a column of air extending from the surface of the Earth to the top of the atmosphere. This parameter can also be referred to as total ozone, or vertically integrated ozone. The values are dominated by ozone within the stratosphere.

In the ECMWF Integrated Forecasting System (IFS), there is a simplified representation of ozone chemistry (including representation of the chemistry which has caused the ozone hole). Ozone is also transported around in the atmosphere through the motion of air. See further documentation .

Naturally occurring ozone in the stratosphere helps protect organisms at the surface of the Earth from the harmful effects of ultraviolet (UV) radiation from the Sun. Ozone near the surface, often produced because of pollution, is harmful to organisms.

In the IFS, the units for total ozone are kilograms per square metre, but before 12/06/2001 dobson units were used. Dobson units (DU) are still used extensively for total column ozone. 1 DU = 2.1415E-5 kg m-2
kg m**-2  
10si 207 10 metre wind speed This parameter is the horizontal speed of the wind, or movement of air, at a height of ten metres above the surface of the Earth. The units of this parameter are metres per second.

Care should be taken when comparing this parameter with observations, because wind observations vary on small space and time scales and are affected by the local terrain, vegetation and buildings that are represented only on average in the ECMWF Integrated Forecasting System.

The eastward and northward components of the horizontal wind at 10m are also available as parameters.
m s**-1  
iews 229 Instantaneous eastward turbulent surface stress Air flowing over a surface exerts a stress that transfers momentum to the surface and slows the wind. This parameter is the stress on the Earth's surface at the specified time in the eastward direction due to both the turbulent interactions between the atmosphere and the surface, and to turbulent orographic form drag.

The turbulent interactions between the atmosphere and the surface are due to the roughness of the surface.

The turbulent orographic form drag is the stress due to the valleys, hills and mountains on horizontal scales below 5km being derived from land surface data at about 1 km resolution. See further information.

Positive (negative) values denote stress in the eastward (westward) direction.
N m**-2  
inss 230 Instantaneous northward turbulent surface stress Air flowing over a surface exerts a stress that transfers momentum to the surface and slows the wind. This parameter is the stress on the Earth's surface at the specified time in the northward direction due to both the turbulent interactions between the atmosphere and the surface, and to turbulent orographic form drag.

The turbulent interactions between the atmosphere and the surface are due to the roughness of the surface.

The turbulent orographic form drag is the stress due to the valleys, hills and mountains on horizontal scales below 5km being derived from land surface data at about 1 km resolution. See further information.

Positive (negative) values denote stress in the northward (southward) direction.
N m**-2  
stl4 236 Soil temperature level 4 This parameter is the temperature of the soil at level 4 (in the middle of layer 4).

The ECMWF Integrated Forecasting System (IFS) has a four-layer representation of soil, where the surface is at 0cm:

Layer 1: 0 - 7cm
Layer 2: 7 - 28cm
Layer 3: 28 - 100cm
Layer 4: 100 - 289cm

Soil temperature is set at the middle of each layer, and heat transfer is calculated at the interfaces between them. It is assumed that there is no heat transfer out of the bottom of the lowest layer.

This parameter has units of Kelvin (K). Temperature measured in Kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

See further information.
K  
fal 243 Forecast albedo This parameter is a measure of the reflectivity of the Earth's surface. It is the fraction of solar (shortwave) radiation reflected by Earth's surface, across the solar spectrum, for both direct and diffuse radiation. Typically, snow and ice have high reflectivity with albedo values of 0.8 and above, land has intermediate values between about 0.1 and 0.4 and the ocean has low values of 0.1 or less.

Radiation from the Sun (solar, or shortwave, radiation) is partly reflected back to space by clouds and particles in the atmosphere (aerosols) and some of it is absorbed. The rest is incident on the Earth's surface, where some of it is reflected. The portion that is reflected by the Earth's surface depends on the albedo. See further documentation .

In the ECMWF Integrated Forecasting System (IFS), a climatological background albedo (observed values averaged over a period of several years) is used, modified by the model over water, ice and snow.

Albedo is often shown as a percentage (%).
(0 - 1)  
msror 172008 Mean surface runoff rate Mean rate of accumulation.
The monthly mean is computed from the rate of accumulation of the field
m of water equivalent s**-1  
mssror 172009 Mean sub-surface runoff rate Deep soil drainage. Mean rate of accumulation.
The monthly mean is computed from the rate of accumulation of the field
m of water equivalent s**-1  
mlsprt 172142 Mean large-scale precipitation rate   m s**-1  
cprate 172143 Mean convective precipitation rate   m s**-1  
mtsfr 172144 Mean total snowfall rate This parameter is the mean rate of snowfall. It is accumulated snowfall divided by the length of the accumulation period, which depends on the data extracted.

This parameter is the sum of large-scale snowfall and convective snowfall. Large-scale snowfall is generated by the cloud scheme in the ECMWF Integrated Forecast System (IFS). The cloud scheme represents the formation and dissipation of clouds and large-scale snowfall due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly by the IFS at spatial scales of a grid box or larger. Convective snowfall is generated by the convection scheme in the IFS. The convection scheme represents convection at spatial scales smaller than the grid box. See further information.

The units are depth of water equivalent in metres which falls per second (i.e., the depth the melted snow would have if it were spread evenly over the grid box ).

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step.
m of water equivalent s**-1  
msshfl 172146 Mean surface sensible heat flux   W m**-2  
mslhfl 172147 Mean surface latent heat flux   W m**-2  
msdsrf 172169 Mean surface downward solar radiation flux   W m**-2  
msdtrf 172175 Mean surface downward thermal radiation flux   W m**-2  
msnsrf 172176 Mean surface net solar radiation flux   W m**-2  
msntrf 172177 Mean surface net thermal radiation flux   W m**-2  
mtnsrf 172178 Mean top net solar radiation flux   W m**-2  
mtntrf 172179 Mean top net thermal radiation flux   W m**-2  
ewssra 172180 East-West surface stress rate of accumulation   N m**-2  
nsssra 172181 North-South surface stress rate of accumulation   N m**-2  
erate 172182 Evaporation   m of water s**-1  
msdr 172189 Mean sunshine duration rate This parameter is the accumulated sunshine duration divided by the length of the accumulation period, which depends on the data extracted, giving the mean sunshine duration rate.

The sunshine duration is the length of time in which the direct solar (shortwave) radiation at the Earth's surface, falling on a plane perpendicular to the direction of the Sun, is greater than or equal to 120 W m-2.

The minimum solar intensity level of 120 W m-2 is defined by the World Meteorological Organisation and is consistent with observed values of sunshine duration from a Campbell-Stokes recorder (sometimes called a Stokes sphere) that can only measure moderately intense sunlight and brighter.
s s**-1  
mrort 172205 Mean runoff rate   m s**-1  
soira 172212 Solar insolation rate of accumulation   W m**-2  
tprate 172228 Mean total precipitation rate This parameter is the mean rate of total precipitation. It is accumulated precipitation divided by the length of the accumulation period, which depends on the data extracted.

In the ECMWF Integrated Forecasting System (IFS), total precipitation is rain and snow that falls to the Earth's surface. It is the sum of large-scale precipitation and convective precipitation. Large-scale precipitation is generated by the cloud scheme in the IFS. The cloud scheme represents the formation and dissipation of clouds and large-scale precipitation due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly by the IFS at spatial scales of a grid box or larger. Convective precipitation is generated by the convection scheme in the IFS. The convection scheme represents convection at spatial scales smaller than the grid box. See further information. Precipitation parameters do not include fog, dew or the precipitation that evaporates in the atmosphere before it lands at the surface of the Earth.

The units are depth of water equivalent in metres which falls per second (i.e., the depth the water would have if it were spread evenly over the grid box).

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step .
m s**-1  
lmlt 228008 Lake mix-layer temperature This parameter is the temperature of the uppermost layer of inland water bodies (lakes, reservoirs and rivers) or coastal waters, that is well mixed and has a near constant temperature with depth (i.e., a uniform distribution of temperature with depth).

The ECMWF Integrated Forecasting System represents inland water bodies and coastal waters with two layers in the vertical, the mixed layer above and the thermocline below. The upper boundary of the thermocline is located at the mixed layer bottom, and the lower boundary of the thermocline at the lake bottom.

Mixing within the mixed layer can occur when the density of the surface (and near-surface) water is greater than that of the water below. Mixing can also occur through the action of wind on the surface of the lake.

This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

ECMWF implemented a lake model in May 2015 to represent the water temperature and lake ice of all the world's major inland water bodies in the Integrated Forecasting System (IFS). The IFS differentiates between (i) ocean water, handled by the ocean model, and (ii) inland water (lakes, reservoirs and rivers) and coastal waters handled by the lake parametrisation. Lake depth and surface area (or fractional cover) are kept constant in time.
K  
licd 228014 Lake ice total depth This parameter is the thickness of ice on inland water bodies (lakes, reservoirs and rivers) and coastal waters.

The ECMWF Integrated Forecasting System represents the formation and melting of ice on inland water bodies. A single ice layer is represented. This parameter is the thickness of that ice layer.

ECMWF implemented a lake model in May 2015 to represent the water temperature and lake ice of all the world's major inland water bodies in the Integrated Forecasting System (IFS). The IFS differentiates between (i) ocean water, handled by the ocean model, and (ii) inland water (lakes, reservoirs and rivers) and coastal waters handled by the lake parametrisation. Lake depth and surface area (or fractional cover) are kept constant in time.
m  

V-i-b: Pressure levels

Available levels 1000, 925, 850, 700, 500, 400, 300, 200 hPa

Short Name ID Long Name Description Units Additional information
t 130 Temperature This parameter is the temperature in the atmosphere.

It has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

This parameter is available on multiple levels through the atmosphere.
K  
u 131 U component of wind This parameter is the eastward component of the wind. It is the horizontal speed of air moving towards the east, in metres per second. A negative sign thus indicates air movement towards the west.

This parameter can be combined with the V component of wind to give the speed and direction of the horizontal wind.
m s**-1  
v 132 V component of wind This parameter is the northward component of the wind. It is the horizontal speed of air moving towards the north, in metres per second. A negative sign thus indicates air movement towards the south.

This parameter can be combined with the U component of wind to give the speed and direction of the horizontal wind.
m s**-1  
q 133 Specific humidity This parameter is the mass of water vapour per kilogram of moist air.

The total mass of moist air is the sum of the dry air, water vapour, cloud liquid, cloud ice, rain and falling snow.
kg kg**-1  
vo 138 Vorticity (relative) This parameter is a measure of the rotation of air in the horizontal, around a vertical axis, relative to a fixed point on the surface of the Earth.

On the scale of weather systems, troughs (weather features that can include rain) are associated with anticlockwise rotation (in the northern hemisphere), and ridges (weather features that bring light or still winds) are associated with clockwise rotation.

Adding the rotation of the Earth, the so-called Coriolis parameter, to the relative vorticity produces the absolute vorticity.
s**-1  
d 155 Divergence This parameter is the horizontal divergence of velocity. It is the rate at which air is spreading out horizontally from a point, per square metre. This parameter is positive for air that is spreading out, or diverging, and negative for the opposite, for air that is concentrating, or converging (convergence). s**-1  
gh 156 Geopotential Height This parameter is a measure of the height of a point in the atmosphere in relation to its potential energy. It is calculated by dividing the geopotential by the Earth's mean gravitational acceleration, g (=9.80665 m s-2). The geopotential is the gravitational potential energy of a unit mass, at a particular location, relative to mean sea level. Geopotential is also the amount of work that would have to be done, against the force of gravity, to lift a unit mass to that location from mean sea level.

This parameter plays an important role in synoptic meteorology (analysis of weather patterns). Charts of geopotential height plotted at constant pressure levels (e.g., 300, 500 or 850 hPa) can be used to identify weather systems such as cyclones, anticyclones, troughs and ridges. At the surface of the Earth, this parameter shows the variations in geopotential height of the surface, and is often referred to as the orography.

The units of this parameter are geopotential metres. A geopotential metre is approximately 2% shorter than a geometric metre.
gpm  
o3 203 Ozone mass mixing ratio This parameter is the mass of ozone per kilogram of air.

In the ECMWF Integrated Forecasting System (IFS), there is a simplified representation of ozone chemistry (including representation of the chemistry which has caused the ozone hole). Ozone is also transported around in the atmosphere through the motion of air. See further documentation.

Naturally occurring ozone in the stratosphere helps protect organisms at the surface of the Earth from the harmful effects of ultraviolet (UV) radiation from the Sun. Ozone near the surface, often produced because of pollution, is harmful to organisms.

Most of the IFS chemical species are archived as mass mixing ratios [kg kg-1]. This link explains how to convert to concentration in terms of mass per unit volume.
kg kg**-1  

V-ii: Monthly mean anomalies of ensemble means

Ranges Base times Resolution
1 to 7 month 00 UTC
  • 0.4° x 0.4° lat/long grid or any multiple thereof (global or sub-area)
  • 0.75° x 0.75° lat/long grid or any multiple thereof (global or sub-area)
  • On model (Gaussian) O320 (35 km) grid (global or sub-area)
  • Spectral components (T319) for upper-air fields (global area only)

V-ii-a: Single level 

Short Name ID Long Name Description Units Additional information
z 129 Geopotential This parameter is the gravitational potential energy of a unit mass, at a particular location, relative to mean sea level. It is also the amount of work that would have to be done, against the force of gravity, to lift a unit mass to that location from mean sea level.

The geopotential height can be calculated by dividing the geopotential by the Earth's gravitational acceleration, g (=9.80665 m s-2). The geopotential height plays an important role in synoptic meteorology (analysis of weather patterns). Charts of geopotential height plotted at constant pressure levels (e.g., 300, 500 or 850 hPa) can be used to identify weather systems such as cyclones, anticyclones, troughs and ridges.

At the surface of the Earth, this parameter shows the variations in geopotential (height) of the surface, and is often referred to as the orography.
m**2 s**-2  
lsm 172 Land-sea mask This parameter is the proportion of land, as opposed to ocean or inland waters (lakes, reservoirs, rivers and coastal waters), in a grid box.
This parameter has values ranging between zero and one and is dimensionless.
In cycles of the ECMWF Integrated Forecasting System (IFS) from CY41R1 (introduced in May 2015) onwards, grid boxes where this parameter has a value above 0.5 can be comprised of a mixture of land and inland water but not ocean. Grid boxes with a value of 0.5 and below can only be comprised of a water surface. In the latter case, the lake cover is used to determine how much of the water surface is ocean or inland water.
In cycles of the IFS before CY41R1, grid boxes where this parameter has a value above 0.5 can only be comprised of land and those grid boxes with a value of 0.5 and below can only be comprised of ocean. In these older model cycles, there is no differentiation between ocean and inland water.
(0 - 1)  
lmlta 171024 Lake mix-layer temperature anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mixed-layer temperature of inland water bodies (lakes, reservoirs and rivers) or coastal waters is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

The mixed-layer temperature is the temperature of the uppermost layer of a lake that is well mixed. The ECMWF Integrated Forecasting System represents inland water bodies and coastal waters with two layers in the vertical, the mixed layer above and the thermocline below, where temperature changes with depth. The upper boundary of the thermocline is located at the mixed layer bottom, and the lower boundary of the thermocline at the lake bottom.

Mixing can occur when the density of the surface (and near-surface) water is greater than that of the water below. Mixing can also occur through the action of wind on the surface of the lake.

ECMWF implemented a lake model in May 2015 to represent the water temperature and lake ice of all the world's major inland water bodies in the Integrated Forecasting System (IFS). The IFS differentiates between (i) ocean water, handled by the ocean model, and (ii) inland water (lakes, reservoirs and rivers) and coastal waters handled by the lake parametrisation. Lake depth and surface area (or fractional cover) are kept constant in time.
K  
licda 171025 Lake ice depth anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the ice thickness on inland water bodies (lakes, reservoirs and rivers) and coastal waters is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

The ECMWF Integrated Forecasting System represents the formation and melting of ice on inland water bodies. A single ice layer is represented. Lake ice depth is the thickness of that ice layer.

ECMWF implemented a lake model in May 2015 to represent the water temperature and lake ice of all the world's major inland water bodies in the Integrated Forecasting System (IFS). The IFS differentiates between (i) ocean water, handled by the ocean model, and (ii) inland water (lakes, reservoirs and rivers) and coastal waters handled by the lake parametrisation. Lake depth and surface area (or fractional cover) are kept constant in time.
m  
sica 171031 Sea-ice cover anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the sea-ice cover is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

Sea-ice cover is the fraction of a grid box which is covered by sea-ice. Sea-ice can only occur in a grid box which is defined as ocean according to the land sea mask at the resolution being used. Sea-ice cover can also be known as sea-ice fraction or sea-ice concentration.

Sea-ice is frozen sea water which floats on the surface of the ocean. Sea-ice does not include ice which forms on land such as glaciers, icebergs and ice-sheets. It also excludes ice shelves which are anchored on land, but protrude out over the surface of the ocean. These phenomena are not modelled by the IFS.

Long-term monitoring of sea-ice cover is important for understanding climate change. Sea-ice cover also affects shipping routes through the polar regions.
(0 - 1)  
rsna 171033 Snow density anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the snow density is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

The ECMWF Integrated Forecast System represents snow as a single additional layer over the uppermost soil level. Snow density is assumed to be constant through the depth of the snow layer. Snow density changes with time due to the weight of snow and melt water in the snowpack.
kg m**-3  
ssta 171034 Sea surface temperature anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the temperature of sea water near the surface is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

Sea surface temperature (SST) is taken from various providers, who process the observational data in different ways. Each provider uses data from several different observational sources. For example, satellites measure SST in a layer a few microns thick in the uppermost mm of the ocean, drifting buoys measure SST at a depth of about 0.2-1.5m, whereas ships sample sea water down to about 10m, while the vessel is underway. Deeper measurements are not affected by changes that occur during a day, due to the rising and setting of the Sun (diurnal variations).

Sometimes SST is taken from a forecast made by coupling the NEMO ocean model to the ECMWF Integrated Forecasting System. In this case, the SST is the average temperature of the uppermost metre of the ocean and does exhibit diurnal variations.

See further SST documentation.
K  
swval1 171039 Volumetric soil water anomaly layer 1 An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the volumetric soil water is larger/smaller in layer 1 than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

Volumetric soil water is the volume of water in soil.

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:

Layer 1: 0 - 7cm

Layer 2: 7 - 28cm

Layer 3: 28 - 100cm

Layer 4: 100 - 289cm

The volumetric soil water is associated with the soil texture (or classification), soil depth, and the underlying groundwater level.
m**3 m**-3  
swval2 171040 Volumetric soil water anomaly layer 2 An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the volumetric soil water is larger/smaller in layer 2 than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

Volumetric soil water is the volume of water in soil.

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:

Layer 1: 0 - 7cm

Layer 2: 7 - 28cm

Layer 3: 28 - 100cm

Layer 4: 100 - 289cm

The volumetric soil water is associated with the soil texture (or classification), soil depth, and the underlying groundwater level.
m**3 m**-3  
swval3 171041 Volumetric soil water anomaly layer 3 An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the volumetric soil water is larger/smaller in layer 3 than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

Volumetric soil water is the volume of water in soil.

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:

Layer 1: 0 - 7cm

Layer 2: 7 - 28cm

Layer 3: 28 - 100cm

Layer 4: 100 - 289cm

The volumetric soil water is associated with the soil texture (or classification), soil depth, and the underlying groundwater level.
m**3 m**-3  
swval4 171042 Volumetric soil water anomaly layer 4 An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the volumetric soil water is larger/smaller in layer 4 than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

Volumetric soil water is the volume of water in soil.

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:

Layer 1: 0 - 7cm

Layer 2: 7 - 28cm

Layer 3: 28 - 100cm

Layer 4: 100 - 289cm

The volumetric soil water is associated with the soil texture (or classification), soil depth, and the underlying groundwater level.
m**3 m**-3  
10fga 171049 10 metre wind gust anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the 10 metre wind gust is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The WMO defines a wind gust as the maximum of the wind averaged over 3 second intervals. This duration is shorter than a model time step, and so the ECMWF Integrated Forecasting System deduces the magnitude of a gust within each time step from the time-step-averaged surface stress, surface friction, wind shear and stability. Then, the maximum wind gust is selected from the gusts at each time step during a particular time period which depends on the data extracted.

This parameter is calculated at a height of ten metres above the surface of the Earth.

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step.
m s**-1  
mx2t24a 171051 Maximum 2 metre temperature in the last 24 hours anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the maximum 2 metre temperature in the previous 24 hours is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

2m temperature is calculated by interpolating between the lowest model level and the Earth's surface, taking account of the atmospheric conditions. See further information.
K  
mn2t24a 171052 Minimum 2 metre temperature in the last 24 hours anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the minimum 2 metre temperature in the previous 24 hours is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

2m temperature is calculated by interpolating between the lowest model level and the Earth's surface, taking account of the atmospheric conditions. See further information.
K  
tclwa 171078 Total column liquid water anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the total amount of cloud liquid water (in a column extending from the surface of the Earth to the top of the atmosphere) is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

This parameter represents the area averaged value for a grid box.

Clouds contain a continuum of different sized water droplets and ice particles. The ECMWF Integrated Forecasting System (IFS) cloud scheme simplifies this to represent a number of discrete cloud droplets/particles including: cloud water droplets, raindrops, ice crystals and snow (aggregated ice crystals). The processes of droplet formation, conversion and aggregation are also highly simplified in the IFS.
kg m**-2  
tciwa 171079 Total column ice water anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the total amount of cloud ice (in a column extending from the surface of the Earth to the top of the atmosphere) is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information). This parameter does not include snow (i.e., precipitating ice).

This parameter represents the area averaged value for a grid box.

Clouds contain a continuum of different sized water droplets and ice particles. The ECMWF Integrated Forecasting System (IFS) cloud scheme simplifies this to represent a number of discrete cloud droplets/particles including: cloud water droplets, raindrops, ice crystals and snow (aggregated ice crystals). The processes of droplet formation, conversion and aggregation are also highly simplified in the IFS.
kg m**-2  
tcwva 171137 Total column water vapour anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the total water vapour (in a column extending from the surface of the Earth to the top of the atmosphere) is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

This parameter represents the area averaged value for a grid box.
kg m**-2  
stal1 171139 Soil temperature anomaly level 1 An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the soil temperature at level 1 (the middle of layer 1) is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:

Layer 1: 0 - 7cm

Layer 2: 7 - 28cm

Layer 3: 28 - 100cm

Layer 4: 100 - 289cm

Soil temperature is set at the middle of each layer, and heat transfer is calculated at the interfaces between them. It is assumed that there is no heat transfer out of the bottom of the lowest layer.

This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

See further information.
K  
sda 171141 Snow depth anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the snow depth is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

The ECMWF Integrated Forecast System represents snow as a single additional layer over the uppermost soil level. The snow may cover all or part of the grid box. Snow depth is the depth the water would have if the snow (from the snow-covered area of a grid box ) melted and was spread evenly over the whole grid box. Therefore, its units are metres of water equivalent.
m of water equivalent  
msla 171151 Mean sea level pressure anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean sea level pressure is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The mean sea level pressure is the pressure (force per unit area) of the atmosphere adjusted to the height of mean sea level. It is a measure of the weight that all the air in a column vertically above the area of Earth's surface would have at that point, if the point were located at the mean sea level. It is calculated over all surfaces - land, sea and in-land water.

Maps of mean sea level pressure are used to identify the locations of low and high pressure systems, often referred to as cyclones and anticyclones. Contours of mean sea level pressure also indicate the strength of the wind. Tightly packed contours show stronger winds.

The units of this parameter are pascals (Pa). Mean sea level pressure is often measured in hPa and sometimes is presented in the old units of millibars, mb (1 hPa = 1 mb = 100 Pa).
Pa  
tcca 171164 Total cloud cover anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that total cloud cover is larger/smaller than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Total cloud cover is the proportion of a model grid box covered by cloud. Total cloud cover is a single level field calculated from the cloud occurring at different model levels through the atmosphere. Assumptions are made about the degree of overlap/randomness between the horizontal positioning of clouds at different heights.
(0 - 1)  
10ua 171165 10 metre U wind component anomaly An anomaly is a difference from a defined long-term average. A positive anomaly indicates that the wind is more eastward (or less westward) than average. A negative anomaly indicates that the wind is more westward (or less eastward) than average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The 10 metre U wind component is the eastward component of the 10 m wind. It is the horizontal speed of air moving towards the east, at a height of ten metres above the surface of the Earth, in metres per second.

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step.
m s**-1  
10va 171166 10 metre V wind component anomaly An anomaly is a difference from a defined long-term average. A positive anomaly indicates that the wind is more northward (or less southward) than average. A negative anomaly indicates that the wind is more southward (or less northward) than average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The 10 metre V wind component is the northward component of the 10 m wind. It is the horizontal speed of air moving towards the north, at a height of ten metres above the surface of the Earth, in metres per second.

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step.
m s**-1  
2ta 171167 2 metre temperature anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the 2 metre temperature is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

2m temperature is calculated by interpolating between the lowest model level and the Earth's surface, taking account of the atmospheric conditions. See further information.
K  
2da 171168 2 metre dewpoint temperature anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the 2 metre dew point temperature is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Dew point temperature is the temperature to which the air would have to be cooled for saturation to occur. It is a measure of the humidity of the air. Combined with temperature and pressure, it can be used to calculate the relative humidity.

2m dew point temperature is calculated by interpolating between the lowest model level and the Earth's surface, taking account of the atmospheric conditions.See further information.
K  
stal2 171170 Soil temperature anomaly level 2 An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the soil temperature at level 2 (the middle of layer 2) is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:

Layer 1: 0 - 7cm

Layer 2: 7 - 28cm

Layer 3: 28 - 100cm

Layer 4: 100 - 289cm

Soil temperature is set at the middle of each layer, and heat transfer is calculated at the interfaces between them. It is assumed that there is no heat transfer out of the bottom of the lowest layer.

This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

See further information.
K  
stal3 171183 Soil temperature anomaly level 3 An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the soil temperature at level 3 (the middle of layer 3) is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:

Layer 1: 0 - 7cm

Layer 2: 7 - 28cm

Layer 3: 28 - 100cm

Layer 4: 100 - 289cm

Soil temperature is set at the middle of each layer, and heat transfer is calculated at the interfaces between them. It is assumed that there is no heat transfer out of the bottom of the lowest layer.

This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

See further information.
K  
lcca 171186 Low cloud cover anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that low cloud cover is larger/smaller than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Low cloud cover is the proportion of a model grid box covered by cloud occurring in the lower levels of the troposphere. Low cloud is a single level field calculated from cloud occurring on model levels with a pressure greater than 0.8 times the surface pressure. So, if the surface pressure is 1000 hPa (hectopascal), low cloud would be calculated using levels with a pressure greater than 800 hPa (below approximately 2 km (assuming a 'standard atmosphere')).

The low cloud cover parameter is calculated from cloud cover for the appropriate model levels as described above. Assumptions are made about the degree of overlap/randomness between the horizontal positioning of clouds in different model levels.
(0 - 1)  
tco3a 171206 Total column ozone anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that total column ozone is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Total column ozone is the total amount of ozone in a column of air extending from the surface of the Earth to the top of the (model) atmosphere. This parameter can also be referred to as total ozone, or vertically integrated ozone. The values are dominated by ozone within the stratosphere.

In the ECMWF Integrated Forecasting System (IFS), there is a simplified representation of ozone chemistry (including representation of the chemistry which has caused the ozone hole). Ozone is also transported around in the atmosphere through the motion of air. See further documentation.

Naturally occurring ozone in the stratosphere helps protect organisms at the surface of the Earth from the harmful effects of ultraviolet (UV) radiation from the Sun. Ozone near the surface, often produced because of pollution, is harmful to organisms.

In the IFS, the units for total ozone are kilograms per square metre, but before 12/06/2001 dobson units were used. Dobson units (DU) are still used extensively for total column ozone. 1 DU = 2.1415E-5 kg m-2.
kg m**-2  
10sia 171207 10 metre wind speed anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the 10 metre wind speed is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The 10 metre wind speed is the horizontal speed of the wind, or movement of air, at a height of ten metres above the surface of the Earth.

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step.
m s**-1  
iewsa 171229 Instantaneous X surface stress anomaly An anomaly is a difference from a defined long-term average. A positive anomaly indicates that the surface stress is more eastward (or less westward) than average. A negative anomaly indicates that the surface stress is more westward (or less eastward) than the average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Air flowing over a surface exerts a stress that transfers momentum to the surface and slows the wind. The instantaneous X surface stress is the stress on the Earth's surface at the specified time in the eastward direction due to both the turbulent interactions between the atmosphere and the surface, and to turbulent orographic form drag.

The turbulent interactions between the atmosphere and the surface are due to the roughness of the surface.

The turbulent orographic form drag is the stress due to the valleys, hills and mountains on horizontal scales below 5km being derived from land surface data at about 1 km resolution. See further information.
N m**-2  
inssa 171230 Instantaneous Y surface stress anomaly An anomaly is a difference from a defined long-term average. A positive anomaly indicates that the surface stress is more northward (or less southward) than average. A negative anomaly indicates that the surface stress is more southward (or less northward) than the average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Air flowing over a surface exerts a stress that transfers momentum to the surface and slows the wind. The instantaneous Y surface stress is the stress on the Earth's surface at the specified time in the northward direction due to both the turbulent interactions between the atmosphere and the surface, and to turbulent orographic form drag.

The turbulent interactions between the atmosphere and the surface are due to the roughness of the surface.

The turbulent orographic form drag is the stress due to the valleys, hills and mountains on horizontal scales below 5km being derived from land surface data at about 1 km resolution. See further information.
N m**-2  
stal4 171236 Soil temperature level 4 anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the soil temperature at level 4 (the middle of layer 4) is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:

Layer 1: 0 - 7cm

Layer 2: 7 - 28cm

Layer 3: 28 - 100cm

Layer 4: 100 - 289cm

Soil temperature is set at the middle of each layer, and heat transfer is calculated at the interfaces between them. It is assumed that there is no heat transfer out of the bottom of the lowest layer.

This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

See further information.
K  
fala 171243 Forecast albedo anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the forecast albedo is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The forecast albedo is a measure of the reflectivity of the Earth's surface. It is the fraction of solar (shortwave) radiation reflected by Earth's surface, across the solar spectrum, for both direct and diffuse radiation. Typically, snow and ice have high reflectivity with albedo values of 0.8 and above, land has intermediate values between about 0.1 and 0.4 and the ocean has low values of 0.1 or less. See further documentation.

In the ECMWF Integrated Forecasting System (IFS), the model only modifies albedo values over water, ice and snow, elsewhere a background climatological albedo is used.
(0 - 1)  
msrora 173008 Mean surface runoff rate anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean surface runoff rate is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The mean surface runoff rate is the amount of water from rainfall or melting snow that is not absorbed by the soil and drains away over the surface. Water may also drain away under the ground. It is the accumulated amount of water, divided by the length of the accumulation period, which depends on the data extracted.

This quantity represents the depth this water would have if it were spread evenly over the grid box.

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step
m of water equivalent s**-1  
mssrora 173009 Mean sub-surface runoff rate anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean sub-surface runoff rate is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The mean sub-surface runoff rate is the amount of water deep in the soil that drains away under the ground. Water may also drain away over the surface. It is the accumulated amount of water, divided by the length of the accumulation period, which depends on the data extracted.

This quantity represents the depth this water would have if it were spread evenly over the grid box.

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step
m of water equivalent s**-1  
lspara 173142 Stratiform precipitation (Large-scale precipitation) anomalous rate of accumulation An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean large-scale precipitation rate is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Mean large-scale precipitation rate is accumulated precipitation divided by the length of the accumulation period, which depends on the data extracted.

For this parameter, precipitation is made up of rain and snow that falls to the Earth's surface, generated by the cloud scheme in the ECMWF Integrated Forecasting System (IFS). The cloud scheme represents the formation and dissipation of clouds and large-scale precipitation due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly by the IFS at spatial scales of a grid box or larger. Precipitation can also be due to convection generated by the convection scheme in the IFS. The convection scheme represents convection at spatial scales smaller than the grid box. See further information.Precipitation parameters do not include fog, dew or the precipitation that evaporates in the atmosphere before it lands at the surface of the Earth.

The units include depth in metres of water equivalent. This is the depth the water would have if it were spread evenly over the grid box.

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step.
m s**-1  
mcpra 173143 Mean convective precipitation rate anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean convective precipitation rate is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

Mean convective precipitation rate is accumulated precipitation divided by the length the accumulation period, which depends on the data extracted.

For this parameter, precipitation is rain and snow that falls to the Earth's surface, generated by the convection scheme in the ECMWF Integrated Forecasting System (IFS). The convection scheme represents convection at spatial scales smaller than the grid box. Total precipitation is made up of convective and large-scale precipitation. Large-scale precipitation is generated by the cloud scheme in the IFS. The cloud scheme represents the formation and dissipation of clouds and large-scale precipitation due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly by the IFS at spatial scales of a grid box or larger. See further information.

The units include depth, in metres of water equivalent. This is the depth the water would have if it were spread evenly over the grid box. Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step .
m s**-1  
sfara 173144 Snowfall (convective + stratiform) anomalous rate of accumulation An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean snowfall rate is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

The mean snowfall rate is the accumulated snowfall divided by the length of the accumulation period, which depends on the data extracted.

Snowfall is the sum of large-scale snowfall and convective snowfall. Large-scale snowfall is generated by the cloud scheme in the ECMWF Integrated Forecast System. The cloud scheme represents the formation and dissipation of clouds and large-scale snowfall due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly by the IFS at spatial scales of a grid box or larger. Convective snowfall is generated by the convection scheme in the IFS. The convection scheme represents convection at spatial scales smaller than the grid box. See further information.

The units are depth of water equivalent in metres which falls per second (i.e., the depth the melted snow would have if it were spread evenly over the grid box ).

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step.
m of water equivalent s**-1  
sshfara 173146 Surface sensible heat flux anomalous rate of accumulation An anomaly is a difference from a defined long-term average. Since the ECMWF convention for vertical fluxes is positive downwards, a positive anomaly means either a larger downward mean surface sensible heat flux or a smaller upward flux, compared with the long-term average. A negative anomaly means either a smaller downward flux or a larger upward flux. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Surface sensible heat flux is the transfer of heat between the Earth's surface and the atmosphere through the effects of turbulent air motion (but excluding any heat transfer resulting from condensation or evaporation). The mean flux is the accumulated flux divided by the length of the accumulation period, which depends on the data extracted.
J m**-2  
slhfara 173147 Surface latent heat flux anomalous rate of accumulation An anomaly is a difference from a defined long-term average. Since the ECMWF convention for vertical fluxes is positive downwards, a positive anomaly means either a larger downward mean surface latent heat flux or a smaller upward flux, compared with the long-term average. A negative anomaly means either a smaller downward flux or a larger upward flux. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The surface latent heat flux is the transfer of latent heat (resulting from evaporation, condensation and other moisture phase changes) between the Earth's surface and the atmosphere through the effects of turbulent air motion. Evaporation from the Earth's surface represents a transfer of energy from the surface to the atmosphere. The mean latent heat flux is the accumulated flux divided by the length of the accumulation period, which depends on the data extracted.
J m**-2  
ssrdara 173169 Surface solar radiation downwards anomalous rate of accumulation   J m**-2  
strdara 173175 Surface thermal radiation downwards anomalous rate of accumulation An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean flux of surface thermal radiation downwards is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Surface thermal radiation downwards is the amount of thermal (also known as longwave or terrestrial) radiation emitted by the atmosphere and clouds that reaches the Earth's surface. It is the amount of radiation passing through a horizontal plane. The mean flux is the accumulated flux divided by the length of the accumulation period, which depends on the data extracted.

The ECMWF convention for vertical fluxes is positive downwards.
J m**-2  
ssrara 173176 Surface solar radiation anomalous rate of accumulation An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean net surface solar radiation flux is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The net surface solar radiation flux is the amount of solar radiation (also known as shortwave radiation) reaching the surface of the Earth (both direct and diffuse) minus the amount reflected by the Earth's surface (which is governed by the albedo). It is the amount of radiation passing through a horizontal plane, not a plane perpendicular to the direction of the Sun. The mean flux is the accumulated flux divided by the length of the accumulation period, which depends on the data extracted.

The ECMWF convention for vertical fluxes is positive downwards.
J m**-2  
strara 173177 Surface thermal radiation anomalous rate of accumulation An anomaly is a difference from a defined long-term average. Since the ECMWF convention for vertical fluxes is positive downwards, a positive anomaly means either a larger downward mean net surface thermal radiation flux or a smaller upward flux, compared with the long-term average. A negative anomaly means either a smaller downward flux or a larger upward flux. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Thermal radiation (also known as longwave or terrestrial radiation) refers to radiation emitted by the atmosphere, clouds and the surface of the Earth. The net surface thermal radiation flux is the difference between downward and upward thermal radiation at the surface of the Earth. It is the amount of radiation passing through a horizontal plane.

The atmosphere and clouds emit thermal radiation in all directions, some of which reaches the surface as downward thermal radiation. The upward thermal radiation at the surface consists of thermal radiation emitted by the surface plus the fraction of downwards thermal radiation reflected upward by the surface. See further documentation

The mean flux is the accumulated flux divided by the length of the accumulation period, which depends on the data extracted.
J m**-2  
tsrara 173178 Top solar radiation anomalous rate of accumulation An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean net flux of solar radiation at the top of the atmosphere is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The net flux of solar radiation (also known as shortwave radiation) at the top of the atmosphere is the incoming solar radiation minus the outgoing solar radiation. It is the amount of radiation passing through a horizontal plane. The incoming solar radiation is the amount received from the Sun. The outgoing solar radiation is the amount reflected and scattered by the Earth's atmosphere and surface. See further documentation.

The mean flux is the accumulated flux divided by the length of the accumulation period, which depends on the data extracted.

The ECMWF convention for vertical fluxes is positive downwards.
J m**-2  
ttrara 173179 Top thermal radiation anomalous rate of accumulation An anomaly is a difference from a defined long-term average. The ECMWF convention for vertical fluxes is positive downwards and the mean flux of thermal radiation at the top of the atmosphere can only be upwards (i.e., negative). Therefore, a positive anomaly means a smaller upward flux of thermal radiation and a negative anomaly means a larger upward flux, compared with the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The mean flux of thermal radiation (also known as longwave or terrestrial) is the thermal radiation emitted to space at the top of the atmosphere. See further documentation. The mean flux is the accumulated flux divided by the length of the accumulation period, which depends on the data extracted.

The thermal radiation emitted to space at the top of the atmosphere is commonly known as the Outgoing Longwave Radiation (OLR) (but taking a flux from the atmosphere to space as positive).
J m**-2  
ewssara 173180 East-West surface stress anomalous rate of accumulation An anomaly is a difference from a defined long-term average. A positive anomaly indicates that the mean East-West surface stress is more eastward (or less westward) than average. A negative anomaly indicates that the mean East-West surface stress is more westward (or less eastward) than the average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Air flowing over a surface exerts a stress that transfers momentum to the surface and slows the wind. The mean East-West surface stress is the accumulated eastward surface stress divided by the length of the accumulation period, which depends on the data extracted.

The East-West surface stress is the stress on the Earth's surface in the eastward direction due to both the turbulent interactions between the atmosphere and the surface, and to turbulent orographic form drag. The turbulent interactions between the atmosphere and the surface are due to the roughness of the surface. The turbulent orographic form drag is the stress due to the valleys, hills and mountains on horizontal scales below 5km being derived from land surface data at about 1 km resolution. See further information.
N m**-2  
nsssara 173181 North-South surface stress anomalous rate of accumulation An anomaly is a difference from a defined long-term average. A positive anomaly indicates that the mean North-South surface stress is more northward (or less southward) than average. A negative anomaly indicates that the mean North-South surface stress is more southward (or less northward) than the average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Air flowing over a surface exerts a stress that transfers momentum to the surface and slows the wind. The mean North-South surface stress is the accumulated northward surface stress divided by the length of the accumulation period, which depends on the data extracted.

The North-South surface stress is the stress on the Earth's surface in the northward direction due to both the turbulent interactions between the atmosphere and the surface, and to turbulent orographic form drag. The turbulent interactions between the atmosphere and the surface are due to the roughness of the surface. The turbulent orographic form drag is the stress due to the valleys, hills and mountains on horizontal scales below 5km being derived from land surface data at about 1 km resolution. See further information.
N m**-2  
evara 173182 Evaporation anomalous rate of accumulation An anomaly is a difference from a defined long-term average. The ECMWF Integrated Forecasting System convention is that downward fluxes are positive. Therefore a positive anomaly means either a larger downward mean evaporation flux (more condensation) or a smaller upward flux (less evaporation), compared with the long-term average. A negative anomaly means either a smaller downward flux or a larger upward flux. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Evaporation is the amount of water that has evaporated from the Earth's surface, including a simplified representation of transpiration (from vegetation), into vapour in the air above.The mean evaporation rate is the accumulated evaporation divided by the length of the accumulation period, which depends on the data extracted.
m of water s**-1  
sundara 173189 Sunshine duration anomalous rate of accumulation An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean sunshine duration rate is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The mean sunshine duration rate is the accumulated sunshine duration divided by the length of the accumulation period, which depends on the data extracted.

The sunshine duration is the length of time in which the direct solar (shortwave) radiation at the Earth's surface, falling on a plane perpendicular to the direction of the Sun, is greater than or equal to 120 W m-2.

The minimum solar intensity level of 120 W m-2 is defined by the World Meteorological Organisation and is consistent with observed values of sunshine duration from a Campbell-Stokes recorder (sometimes called a Stokes sphere) that can only measure moderately intense sunlight and brighter.
dimensionless  
roara 173205 Runoff anomalous rate of accumulation An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean runoff rate is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The mean runoff rate is the total amount of water from rainfall, melting snow, or deep in the soil, that drains away over the surface and under the ground. It is the accumulated amount of water, divided by the length of the accumulation period, which depends on the data extracted.

This quantity represents the depth this water would have if it were spread evenly over the grid box.

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step.
m s**-1  
soiara 173212 Solar insolation anomalous rate of accumulation An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean solar insolation is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Solar insolation is the incoming radiation from the Sun (also known as solar or shortwave radiation) at the top of the atmosphere (TOA). It is the amount of radiation passing through a horizontal plane, not a plane perpendicular to the direction of the Sun.

Solar insolation has a diurnal cycle (as it is defined into a horizontal plane and not a plane perpendicular to the Sun), as well as an annual cycle due to the change in Sun-Earth distance, and the approximately 11-year solar cycle. Solar insolation at the TOA has experienced no absorption, scattering or reflection within the atmosphere (e.g., from clouds, water vapour, ozone, trace gases and aerosol).

The mean flux is the accumulated flux divided by the length of the accumulation period, which depends on the data extracted. The ECMWF convention for vertical fluxes is positive downwards.
W m**-2 s**-1  
tpara 173228 Total precipitation anomalous rate of accumulation An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean precipitation rate is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The mean precipitation rate is the accumulated precipitation divided by the length of the accumulation period, which depends on the data extracted.

In the ECMWF Integrated Forecasting System (IFS), total precipitation is rain and snow that falls to the Earth's surface. It is the sum of large-scale precipitation and convective precipitation. Large-scale precipitation is generated by the cloud scheme in the IFS. The cloud scheme represents the formation and dissipation of clouds and large-scale precipitation due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly by the IFS at spatial scales of a grid box or larger. Convective precipitation is generated by the convection scheme in the IFS. The convection scheme represents convection at spatial scales smaller than the grid box. See further information. Precipitation parameters do not include fog, dew or the precipitation that evaporates in the atmosphere before it lands at the surface of the Earth.

The units are depth of water equivalent in metres which falls per second. It is the depth the water would have if it were spread evenly over the grid box.

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step .
m s**-1  

V-ii-b Pressure levels

Short Name ID Long Name Description Units Additional information
za 171129 Geopotential anomaly   m**2 s**-2  
ta 171130 Temperature anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that temperature is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

This parameter is available on multiple levels through the atmosphere.
K  
ua 171131 U component of wind anomaly An anomaly is a difference from a defined long-term average. A positive anomaly indicates that the wind is more eastward (or less westward) than average. A negative anomaly indicates that the wind is more westward (or less eastward) than average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The U component of wind is the eastward component of the wind. It is the horizontal speed of air moving towards the east, in metres per second. A negative U component of wind thus indicates air movement towards the west.
m s**-1  
va 171132 V component of wind anomaly An anomaly is a difference from a defined long-term average. A positive anomaly indicates that the wind is more northward (or less southward) than average. A negative anomaly indicates that the wind is more southward (or less northward) than average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The V component of wind is the northward component of the wind. It is the horizontal speed of air moving towards the north, in metres per second. A negative V component of wind thus indicates air movement towards the south.
m s**-1  
qa 171133 Specific humidity anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the specific humidity is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

Specific humidity is the mass of water vapour per kilogram of moist air. The total mass of moist air is the sum of the dry air, water vapour, cloud liquid, cloud ice, rain and falling snow.
kg kg**-1  
voa 171138 Relative vorticity anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the relative vorticity is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Relative vorticity is a measure of the rotation of air in the horizontal, around a vertical axis, relative to a fixed point on the surface of the Earth.

On the scale of weather systems, low pressure systems (weather features that can include rain) are associated with anticlockwise rotation (in the northern hemisphere), and high pressure systems (weather features that bring light or still winds) are associated with clockwise rotation.

Adding the effect of rotation of the Earth, the Coriolis parameter, to the relative vorticity produces the absolute vorticity.
s**-1  
da 171155 Relative divergence anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the relative divergence is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The relative divergence, also called simply the divergence, is the horizontal divergence of velocity. It is the rate at which air is spreading out horizontally from a point, per square metre. This parameter is positive for air that is spreading out, or diverging, and negative for the opposite, for air that is concentrating, or converging (convergence).
s**-1  
gha 171156 Height anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that geopotential height is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Geopotential height is a measure of the height of a point in the atmosphere in relation to its potential energy. It is calculated by dividing the geopotential by the Earth's mean gravitational acceleration, g (=9.80665 m s-2). The geopotential is the gravitational potential energy of a unit mass, at a particular location, relative to mean sea level. Geopotential is also the amount of work that would have to be done, against the force of gravity, to lift a unit mass to that location from mean sea level.

Geopotential height plays an important role in synoptic meteorology (analysis of weather patterns). Charts of geopotential height plotted at constant pressure levels (e.g., 300, 500 or 850 hPa) can be used to identify weather systems such as cyclones, anticyclones, troughs and ridges.

The units of this parameter are geopotential metres. A geopotential metre is 2% shorter than a dynamic metre (also called a geodynamic metre).
m  
o3a 171203 Ozone mass mixing ratio anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that ozone mass mixing ratio is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Ozone mass mixing ratio is the mass of ozone per kilogram of air.

In the ECMWF Integrated Forecasting System (IFS), there is a simplified representation of ozone chemistry (including representation of the chemistry which has caused the ozone hole). Ozone is also transported around in the atmosphere through the motion of air. See further documentation.

Naturally occurring ozone in the stratosphere helps protect organisms at the surface of the Earth from the harmful effects of ultraviolet (UV) radiation from the Sun. Ozone near the surface, often produced because of pollution, is harmful to organisms.

Most of the IFS chemical species are archived as mass mixing ratios [kg kg-1]. This link explains how to convert to concentration in terms of mass per unit volume.
kg kg**-1  

V-iii: Monthly means of individual ensemble members

Ranges Forecast time step Base times Resolution
1 to 7 month 6-hourly 00 UTC
  • 0.4° x 0.4° lat/long grid or any multiple thereof (global or sub-area)
  • 0.75° x 0.75° lat/long grid or any multiple thereof (global or sub-area)
  • On model (Gaussian) O320 (35 km) grid (global or sub-area)
  • Spectral components (T319) for upper-air fields (global area only)

 V-iii-a: Single level 

Short Name ID Long Name Description Units Additional information
ci 31 Sea ice area fraction This parameter is the fraction of a grid box which is covered by sea ice. Sea ice can only occur in a grid box which includes ocean or inland water according to the land sea mask and lake cover, at the resolution being used. This parameter can be known as sea-ice (area) fraction, sea-ice concentration and more generally as sea-ice cover.

Coupled atmosphere ocean simulations of the ECMWF Integrated Forecasting System (IFS) predict the formation and melting of sea ice. Otherwise, in analyses and atmosphere only simulations, sea ice is derived from observations, but the model does take account of the way that sea ice alters the interaction between the atmosphere and ocean.

Sea ice is frozen sea water which floats on the surface of the ocean. Sea ice does not include ice which forms on land such as glaciers, icebergs and ice-sheets. It also excludes ice shelves which are anchored on land, but protrude out over the surface of the ocean. These phenomena are not modelled by the IFS.

Long-term monitoring of sea ice is important for understanding climate change. Sea ice also affects shipping routes through the polar regions.
(0 - 1)  
rsn 33 Snow density This parameter is the mass of snow per cubic metre in the snow layer.

The ECMWF Integrated Forecast System (IFS) model represents snow as a single additional layer over the uppermost soil level. The snow may cover all or part of the grid box.

See further information on snow in the IFS.
kg m**-3  
sst 34 Sea surface temperature This parameter is the temperature of sea water near the surface.

This parameter is taken from various providers, who process the observational data in different ways. Each provider uses data from several different observational sources. For example, satellites measure sea surface temperature (SST) in a layer a few microns thick in the uppermost mm of the ocean, drifting buoys measure SST at a depth of about 0.2-1.5m, whereas ships sample sea water down to about 10m, while the vessel is underway. Deeper measurements are not affected by changes that occur during a day, due to the rising and setting of the Sun (diurnal variations).

Sometimes this parameter is taken from a forecast made by coupling the NEMO ocean model to the ECMWF Integrated Forecasting System. In this case, the SST is the average temperature of the uppermost metre of the ocean and does exhibit diurnal variations.

See further documentation .

This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.
K  
swvl1 39 Volumetric soil water layer 1 This parameter is the volume of water in soil layer 1 (0 - 7cm, the surface is at 0cm).

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:
Layer 1: 0 - 7cm
Layer 2: 7 - 28cm
Layer 3: 28 - 100cm
Layer 4: 100 - 289cm

The volumetric soil water is associated with the soil texture (or classification), soil depth, and the underlying groundwater level.
m**3 m**-3  
swvl2 40 Volumetric soil water layer 2 This parameter is the volume of water in soil layer 2 (7 - 28cm, the surface is at 0cm).

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:
Layer 1: 0 - 7cm
Layer 2: 7 - 28cm
Layer 3: 28 - 100cm
Layer 4: 100 - 289cm

The volumetric soil water is associated with the soil texture (or classification), soil depth, and the underlying groundwater level.
m**3 m**-3  
swvl3 41 Volumetric soil water layer 3 This parameter is the volume of water in soil layer 3 (28 - 100cm, the surface is at 0cm).

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:
Layer 1: 0 - 7cm
Layer 2: 7 - 28cm
Layer 3: 28 - 100cm
Layer 4: 100 - 289cm

The volumetric soil water is associated with the soil texture (or classification), soil depth, and the underlying groundwater level.
m**3 m**-3  
swvl4 42 Volumetric soil water layer 4 This parameter is the volume of water in soil layer 4 (100 - 289cm, the surface is at 0cm).

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:
Layer 1: 0 - 7cm
Layer 2: 7 - 28cm
Layer 3: 28 - 100cm
Layer 4: 100 - 289cm

The volumetric soil water is associated with the soil texture (or classification), soil depth, and the underlying groundwater level.
m**3 m**-3  
10fg 49 10 metre wind gust since previous post-processing Maximum 3 second wind at 10 m height as defined by WMO.

Parametrization represents turbulence only before 01102008; thereafter effects of convection are included. The 3 s gust is computed every time step and and the maximum is kept since the last postprocessing.
m s**-1  
mx2t24 51 Maximum temperature at 2 metres in the last 24 hours The highest value of 2 metre temperature in the previous 24 hour period.

2m temperature is calculated by interpolating between the lowest model level and the Earth's surface, taking account of the atmospheric conditions. See further information.

This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.
K  
mn2t24 52 Minimum temperature at 2 metres in the last 24 hours The lowest value of 2 metre temperature in the previous 24 hour period.

2m temperature is calculated by interpolating between the lowest model level and the Earth's surface, taking account of the atmospheric conditions. See further information.

This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.
K  
tclw 78 Total column cloud liquid water This parameter is the amount of liquid water contained within cloud droplets in a column extending from the surface of the Earth to the top of the atmosphere. Rain water droplets, which are much larger in size (and mass), are not included in this parameter.

This parameter represents the area averaged value for a model grid box.

Clouds contain a continuum of different- sized water droplets and ice particles. The ECMWF Integrated Forecasting System (IFS) cloud scheme simplifies this to represent a number of discrete cloud droplets/particles including: cloud water droplets, raindrops, ice crystals and snow (aggregated ice crystals). The processes of droplet formation, phase transition and aggregation are also highly simplified in the IFS.
kg m**-2  
tciw 79 Total column cloud ice water This parameter is the amount of ice contained within clouds in a column extending from the surface of the Earth to the top of the atmosphere. Snow (aggregated ice crystals) is not included in this parameter.

This parameter represents the area averaged value for a model grid box.

Clouds contain a continuum of different- sized water droplets and ice particles. The ECMWF Integrated Forecasting System (IFS) cloud scheme simplifies this to represent a number of discrete cloud droplets/particles including: cloud water droplets, raindrops, ice crystals and snow (aggregated ice crystals). The processes of droplet formation, phase transition and aggregation are also highly simplified in the IFS.
kg m**-2  
z 129 Geopotential This parameter is the gravitational potential energy of a unit mass, at a particular location, relative to mean sea level. It is also the amount of work that would have to be done, against the force of gravity, to lift a unit mass to that location from mean sea level.

The geopotential height can be calculated by dividing the geopotential by the Earth's gravitational acceleration, g (=9.80665 m s-2). The geopotential height plays an important role in synoptic meteorology (analysis of weather patterns). Charts of geopotential height plotted at constant pressure levels (e.g., 300, 500 or 850 hPa) can be used to identify weather systems such as cyclones, anticyclones, troughs and ridges.

At the surface of the Earth, this parameter shows the variations in geopotential (height) of the surface, and is often referred to as the orography.
m**2 s**-2  
tcwv 137 Total column water vapour This parameter is the total amount of water vapour in a column extending from the surface of the Earth to the top of the atmosphere.

This parameter represents the area averaged value for a grid box.
kg m**-2  
stl1 139 Soil temperature level 1 This parameter is the temperature of the soil at level 1 (in the middle of layer 1).

The ECMWF Integrated Forecasting System (IFS) has a four-layer representation of soil, where the surface is at 0cm:

Layer 1: 0 - 7cm
Layer 2: 7 - 28cm
Layer 3: 28 - 100cm
Layer 4: 100 - 289cm

Soil temperature is set at the middle of each layer, and heat transfer is calculated at the interfaces between them. It is assumed that there is no heat transfer out of the bottom of the lowest layer.

This parameter has units of Kelvin (K). Temperature measured in Kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

See further information.
K  
sd 141 Snow depth This parameter is the depth of snow from the snow-covered area of a grid box.

Its units are metres of water equivalent, so it is the depth the water would have if the snow melted and was spread evenly over the whole grid box. The ECMWF Integrated Forecast System represents snow as a single additional layer over the uppermost soil level. The snow may cover all or part of the grid box.

See further information.
m of water equivalent  
msl 151 Mean sea level pressure This parameter is the pressure (force per unit area) of the atmosphere adjusted to the height of mean sea level.

It is a measure of the weight that all the air in a column vertically above the area of Earth's surface would have at that point, if the point were located at the mean sea level. It is calculated over all surfaces - land, sea and in-land water.

Maps of mean sea level pressure are used to identify the locations of low and high pressure systems, often referred to as cyclones and anticyclones. Contours of mean sea level pressure also indicate the strength of the wind. Tightly packed contours show stronger winds.

The units of this parameter are pascals (Pa). Mean sea level pressure is often measured in hPa and sometimes is presented in the old units of millibars, mb (1 hPa = 1 mb = 100 Pa).
Pa  
tcc 164 Total cloud cover This parameter is the proportion of a grid box covered by cloud. Total cloud cover is a single level field calculated from the cloud occurring at different model levels through the atmosphere. Assumptions are made about the degree of overlap/randomness between clouds at different heights.

Cloud fractions vary from 0 to 1.
(0 - 1)  
10u 165 10 metre U wind component This parameter is the eastward component of the 10m wind. It is the horizontal speed of air moving towards the east, at a height of ten metres above the surface of the Earth, in metres per second.

Care should be taken when comparing this parameter with observations, because wind observations vary on small space and time scales and are affected by the local terrain, vegetation and buildings that are represented only on average in the ECMWF Integrated Forecasting System.

This parameter can be combined with the V component of 10m wind to give the speed and direction of the horizontal 10m wind.
m s**-1  
10v 166 10 metre V wind component This parameter is the northward component of the 10m wind. It is the horizontal speed of air moving towards the north, at a height of ten metres above the surface of the Earth, in metres per second.

Care should be taken when comparing this parameter with observations, because wind observations vary on small space and time scales and are affected by the local terrain, vegetation and buildings that are represented only on average in the ECMWF Integrated Forecasting System.

This parameter can be combined with the U component of 10m wind to give the speed and direction of the horizontal 10m wind.
m s**-1  
2t 167 2 metre temperature This parameter is the temperature of air at 2m above the surface of land, sea or in-land waters.

2m temperature is calculated by interpolating between the lowest model level and the Earth's surface, taking account of the atmospheric conditions. See further information .

This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.
K  
2d 168 2 metre dewpoint temperature This parameter is the temperature to which the air, at 2 metres above the surface of the Earth, would have to be cooled for saturation to occur.

It is a measure of the humidity of the air. Combined with temperature and pressure, it can be used to calculate the relative humidity.

2m dew point temperature is calculated by interpolating between the lowest model level and the Earth's surface, taking account of the atmospheric conditions. See further information.This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.
K  
stl2 170 Soil temperature level 2 This parameter is the temperature of the soil at level 2 (in the middle of layer 2).

The ECMWF Integrated Forecasting System (IFS) has a four-layer representation of soil, where the surface is at 0cm:

Layer 1: 0 - 7cm
Layer 2: 7 - 28cm
Layer 3: 28 - 100cm
Layer 4: 100 - 289cm

Soil temperature is set at the middle of each layer, and heat transfer is calculated at the interfaces between them. It is assumed that there is no heat transfer out of the bottom of the lowest layer.

This parameter has units of Kelvin (K). Temperature measured in Kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

See further information.
K  
lsm 172 Land-sea mask This parameter is the proportion of land, as opposed to ocean or inland waters (lakes, reservoirs, rivers and coastal waters), in a grid box.
This parameter has values ranging between zero and one and is dimensionless.
In cycles of the ECMWF Integrated Forecasting System (IFS) from CY41R1 (introduced in May 2015) onwards, grid boxes where this parameter has a value above 0.5 can be comprised of a mixture of land and inland water but not ocean. Grid boxes with a value of 0.5 and below can only be comprised of a water surface. In the latter case, the lake cover is used to determine how much of the water surface is ocean or inland water.
In cycles of the IFS before CY41R1, grid boxes where this parameter has a value above 0.5 can only be comprised of land and those grid boxes with a value of 0.5 and below can only be comprised of ocean. In these older model cycles, there is no differentiation between ocean and inland water.
(0 - 1)  
stl3 183 Soil temperature level 3 This parameter is the temperature of the soil at level 3 (in the middle of layer 3).

The ECMWF Integrated Forecasting System (IFS) has a four-layer representation of soil, where the surface is at 0cm:

Layer 1: 0 - 7cm
Layer 2: 7 - 28cm
Layer 3: 28 - 100cm
Layer 4: 100 - 289cm

Soil temperature is set at the middle of each layer, and heat transfer is calculated at the interfaces between them. It is assumed that there is no heat transfer out of the bottom of the lowest layer.

This parameter has units of Kelvin (K). Temperature measured in Kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

See further information.
K  
lcc 186 Low cloud cover This parameter is the proportion of a grid box covered by cloud occurring in the lower levels of the troposphere. Low cloud is a single level field calculated from cloud occurring on model levels with a pressure greater than 0.8 times the surface pressure. So, if the surface pressure is 1000 hPa (hectopascal), low cloud would be calculated using levels with a pressure greater than 800 hPa (below approximately 2km (assuming a 'standard atmosphere')).

The low cloud cover parameter is calculated from cloud cover for the appropriate model levels as described above. Assumptions are made about the degree of overlap/randomness between clouds in different model levels.

Cloud fractions vary from 0 to 1.
(0 - 1)  
tco3 206 Total column ozone This parameter is the total amount of ozone in a column of air extending from the surface of the Earth to the top of the atmosphere. This parameter can also be referred to as total ozone, or vertically integrated ozone. The values are dominated by ozone within the stratosphere.

In the ECMWF Integrated Forecasting System (IFS), there is a simplified representation of ozone chemistry (including representation of the chemistry which has caused the ozone hole). Ozone is also transported around in the atmosphere through the motion of air. See further documentation .

Naturally occurring ozone in the stratosphere helps protect organisms at the surface of the Earth from the harmful effects of ultraviolet (UV) radiation from the Sun. Ozone near the surface, often produced because of pollution, is harmful to organisms.

In the IFS, the units for total ozone are kilograms per square metre, but before 12/06/2001 dobson units were used. Dobson units (DU) are still used extensively for total column ozone. 1 DU = 2.1415E-5 kg m-2
kg m**-2  
10si 207 10 metre wind speed This parameter is the horizontal speed of the wind, or movement of air, at a height of ten metres above the surface of the Earth. The units of this parameter are metres per second.

Care should be taken when comparing this parameter with observations, because wind observations vary on small space and time scales and are affected by the local terrain, vegetation and buildings that are represented only on average in the ECMWF Integrated Forecasting System.

The eastward and northward components of the horizontal wind at 10m are also available as parameters.
m s**-1  
iews 229 Instantaneous eastward turbulent surface stress Air flowing over a surface exerts a stress that transfers momentum to the surface and slows the wind. This parameter is the stress on the Earth's surface at the specified time in the eastward direction due to both the turbulent interactions between the atmosphere and the surface, and to turbulent orographic form drag.

The turbulent interactions between the atmosphere and the surface are due to the roughness of the surface.

The turbulent orographic form drag is the stress due to the valleys, hills and mountains on horizontal scales below 5km being derived from land surface data at about 1 km resolution. See further information.

Positive (negative) values denote stress in the eastward (westward) direction.
N m**-2  
inss 230 Instantaneous northward turbulent surface stress Air flowing over a surface exerts a stress that transfers momentum to the surface and slows the wind. This parameter is the stress on the Earth's surface at the specified time in the northward direction due to both the turbulent interactions between the atmosphere and the surface, and to turbulent orographic form drag.

The turbulent interactions between the atmosphere and the surface are due to the roughness of the surface.

The turbulent orographic form drag is the stress due to the valleys, hills and mountains on horizontal scales below 5km being derived from land surface data at about 1 km resolution. See further information.

Positive (negative) values denote stress in the northward (southward) direction.
N m**-2  
stl4 236 Soil temperature level 4 This parameter is the temperature of the soil at level 4 (in the middle of layer 4).

The ECMWF Integrated Forecasting System (IFS) has a four-layer representation of soil, where the surface is at 0cm:

Layer 1: 0 - 7cm
Layer 2: 7 - 28cm
Layer 3: 28 - 100cm
Layer 4: 100 - 289cm

Soil temperature is set at the middle of each layer, and heat transfer is calculated at the interfaces between them. It is assumed that there is no heat transfer out of the bottom of the lowest layer.

This parameter has units of Kelvin (K). Temperature measured in Kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

See further information.
K  
fal 243 Forecast albedo This parameter is a measure of the reflectivity of the Earth's surface. It is the fraction of solar (shortwave) radiation reflected by Earth's surface, across the solar spectrum, for both direct and diffuse radiation. Typically, snow and ice have high reflectivity with albedo values of 0.8 and above, land has intermediate values between about 0.1 and 0.4 and the ocean has low values of 0.1 or less.

Radiation from the Sun (solar, or shortwave, radiation) is partly reflected back to space by clouds and particles in the atmosphere (aerosols) and some of it is absorbed. The rest is incident on the Earth's surface, where some of it is reflected. The portion that is reflected by the Earth's surface depends on the albedo. See further documentation .

In the ECMWF Integrated Forecasting System (IFS), a climatological background albedo (observed values averaged over a period of several years) is used, modified by the model over water, ice and snow.

Albedo is often shown as a percentage (%).
(0 - 1)  
mlsprt 172142 Mean large-scale precipitation rate   m s**-1  
cprate 172143 Mean convective precipitation rate   m s**-1  
mtsfr 172144 Mean total snowfall rate This parameter is the mean rate of snowfall. It is accumulated snowfall divided by the length of the accumulation period, which depends on the data extracted.

This parameter is the sum of large-scale snowfall and convective snowfall. Large-scale snowfall is generated by the cloud scheme in the ECMWF Integrated Forecast System (IFS). The cloud scheme represents the formation and dissipation of clouds and large-scale snowfall due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly by the IFS at spatial scales of a grid box or larger. Convective snowfall is generated by the convection scheme in the IFS. The convection scheme represents convection at spatial scales smaller than the grid box. See further information.

The units are depth of water equivalent in metres which falls per second (i.e., the depth the melted snow would have if it were spread evenly over the grid box ).

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step.
m of water equivalent s**-1  
msshfl 172146 Mean surface sensible heat flux   W m**-2  
mslhfl 172147 Mean surface latent heat flux   W m**-2  
msdsrf 172169 Mean surface downward solar radiation flux   W m**-2  
msdtrf 172175 Mean surface downward thermal radiation flux   W m**-2  
msnsrf 172176 Mean surface net solar radiation flux   W m**-2  
msntrf 172177 Mean surface net thermal radiation flux   W m**-2  
mtnsrf 172178 Mean top net solar radiation flux   W m**-2  
mtntrf 172179 Mean top net thermal radiation flux   W m**-2  
ewssra 172180 East-West surface stress rate of accumulation   N m**-2  
nsssra 172181 North-South surface stress rate of accumulation   N m**-2  
erate 172182 Evaporation   m of water s**-1  
msdr 172189 Mean sunshine duration rate This parameter is the accumulated sunshine duration divided by the length of the accumulation period, which depends on the data extracted, giving the mean sunshine duration rate.

The sunshine duration is the length of time in which the direct solar (shortwave) radiation at the Earth's surface, falling on a plane perpendicular to the direction of the Sun, is greater than or equal to 120 W m-2.

The minimum solar intensity level of 120 W m-2 is defined by the World Meteorological Organisation and is consistent with observed values of sunshine duration from a Campbell-Stokes recorder (sometimes called a Stokes sphere) that can only measure moderately intense sunlight and brighter.
s s**-1  
mrort 172205 Mean runoff rate   m s**-1  
soira 172212 Solar insolation rate of accumulation   W m**-2  
tprate 172228 Mean total precipitation rate This parameter is the mean rate of total precipitation. It is accumulated precipitation divided by the length of the accumulation period, which depends on the data extracted.

In the ECMWF Integrated Forecasting System (IFS), total precipitation is rain and snow that falls to the Earth's surface. It is the sum of large-scale precipitation and convective precipitation. Large-scale precipitation is generated by the cloud scheme in the IFS. The cloud scheme represents the formation and dissipation of clouds and large-scale precipitation due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly by the IFS at spatial scales of a grid box or larger. Convective precipitation is generated by the convection scheme in the IFS. The convection scheme represents convection at spatial scales smaller than the grid box. See further information. Precipitation parameters do not include fog, dew or the precipitation that evaporates in the atmosphere before it lands at the surface of the Earth.

The units are depth of water equivalent in metres which falls per second (i.e., the depth the water would have if it were spread evenly over the grid box).

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step .
m s**-1  
lmlt 228008 Lake mix-layer temperature This parameter is the temperature of the uppermost layer of inland water bodies (lakes, reservoirs and rivers) or coastal waters, that is well mixed and has a near constant temperature with depth (i.e., a uniform distribution of temperature with depth).

The ECMWF Integrated Forecasting System represents inland water bodies and coastal waters with two layers in the vertical, the mixed layer above and the thermocline below. The upper boundary of the thermocline is located at the mixed layer bottom, and the lower boundary of the thermocline at the lake bottom.

Mixing within the mixed layer can occur when the density of the surface (and near-surface) water is greater than that of the water below. Mixing can also occur through the action of wind on the surface of the lake.

This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

ECMWF implemented a lake model in May 2015 to represent the water temperature and lake ice of all the world's major inland water bodies in the Integrated Forecasting System (IFS). The IFS differentiates between (i) ocean water, handled by the ocean model, and (ii) inland water (lakes, reservoirs and rivers) and coastal waters handled by the lake parametrisation. Lake depth and surface area (or fractional cover) are kept constant in time.
K  
licd 228014 Lake ice total depth This parameter is the thickness of ice on inland water bodies (lakes, reservoirs and rivers) and coastal waters.

The ECMWF Integrated Forecasting System represents the formation and melting of ice on inland water bodies. A single ice layer is represented. This parameter is the thickness of that ice layer.

ECMWF implemented a lake model in May 2015 to represent the water temperature and lake ice of all the world's major inland water bodies in the Integrated Forecasting System (IFS). The IFS differentiates between (i) ocean water, handled by the ocean model, and (ii) inland water (lakes, reservoirs and rivers) and coastal waters handled by the lake parametrisation. Lake depth and surface area (or fractional cover) are kept constant in time.
m  

V-iii-b: Pressure levels

Available at 1000, 925, 850, 700, 500, 400, 300, 200 hPa unless otherwise specified.

Short Name ID Long Name Description Units Additional information
t 130 Temperature This parameter is the temperature in the atmosphere.

It has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

This parameter is available on multiple levels through the atmosphere.
K  
u 131 U component of wind This parameter is the eastward component of the wind. It is the horizontal speed of air moving towards the east, in metres per second. A negative sign thus indicates air movement towards the west.

This parameter can be combined with the V component of wind to give the speed and direction of the horizontal wind.
m s**-1  
v 132 V component of wind This parameter is the northward component of the wind. It is the horizontal speed of air moving towards the north, in metres per second. A negative sign thus indicates air movement towards the south.

This parameter can be combined with the U component of wind to give the speed and direction of the horizontal wind.
m s**-1  
q 133 Specific humidity This parameter is the mass of water vapour per kilogram of moist air.

The total mass of moist air is the sum of the dry air, water vapour, cloud liquid, cloud ice, rain and falling snow.
kg kg**-1  
vo 138 Vorticity (relative) This parameter is a measure of the rotation of air in the horizontal, around a vertical axis, relative to a fixed point on the surface of the Earth.

On the scale of weather systems, troughs (weather features that can include rain) are associated with anticlockwise rotation (in the northern hemisphere), and ridges (weather features that bring light or still winds) are associated with clockwise rotation.

Adding the rotation of the Earth, the so-called Coriolis parameter, to the relative vorticity produces the absolute vorticity.
s**-1  
d 155 Divergence This parameter is the horizontal divergence of velocity. It is the rate at which air is spreading out horizontally from a point, per square metre. This parameter is positive for air that is spreading out, or diverging, and negative for the opposite, for air that is concentrating, or converging (convergence). s**-1  
gh 156 Geopotential Height This parameter is a measure of the height of a point in the atmosphere in relation to its potential energy. It is calculated by dividing the geopotential by the Earth's mean gravitational acceleration, g (=9.80665 m s-2). The geopotential is the gravitational potential energy of a unit mass, at a particular location, relative to mean sea level. Geopotential is also the amount of work that would have to be done, against the force of gravity, to lift a unit mass to that location from mean sea level.

This parameter plays an important role in synoptic meteorology (analysis of weather patterns). Charts of geopotential height plotted at constant pressure levels (e.g., 300, 500 or 850 hPa) can be used to identify weather systems such as cyclones, anticyclones, troughs and ridges. At the surface of the Earth, this parameter shows the variations in geopotential height of the surface, and is often referred to as the orography.

The units of this parameter are geopotential metres. A geopotential metre is approximately 2% shorter than a geometric metre.
gpm  
o3 203 Ozone mass mixing ratio This parameter is the mass of ozone per kilogram of air.

In the ECMWF Integrated Forecasting System (IFS), there is a simplified representation of ozone chemistry (including representation of the chemistry which has caused the ozone hole). Ozone is also transported around in the atmosphere through the motion of air. See further documentation.

Naturally occurring ozone in the stratosphere helps protect organisms at the surface of the Earth from the harmful effects of ultraviolet (UV) radiation from the Sun. Ozone near the surface, often produced because of pollution, is harmful to organisms.

Most of the IFS chemical species are archived as mass mixing ratios [kg kg-1]. This link explains how to convert to concentration in terms of mass per unit volume.
kg kg**-1  

V-iii-c Seasonal forecast wave monthly means

Short Name ID Long Name Description Units Additional information
mp1 140220 Mean wave period based on first moment This parameter is the reciprocal of the mean frequency of the wave components that represent the sea state. All wave components have been averaged proportionally to their respective amplitude. This parameter can be used to estimate the magnitude of Stokes drift transport in deep water.

The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). Moments are statistical quantities derived from the two-dimensional wave spectrum.
s  
mp2 140221 Mean zero-crossing wave period This parameter represents the mean length of time between occasions where the sea/ocean surface crosses mean sea level. In combination with wave height information, it could be used to assess the length of time that a coastal structure might be under water, for example.

The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). In the ECMWF Integrated Forecasting System this parameter is calculated from the characteristics of the two-dimensional wave spectrum.
s  
swh 140229 Significant height of combined wind waves and swell This parameter represents the average height of the highest third of surface ocean/sea waves generated by wind and swell. It represents the vertical distance between the wave crest and the wave trough.

The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum).

The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. This parameter takes account of both.

More strictly, this parameter is four times the square root of the integral over all directions and all frequencies of the two-dimensional wave spectrum. See further documentation.

This parameter can be used to assess sea state and swell. For example, engineers use significant wave height to calculate the load on structures in the open ocean, such as oil platforms, or in coastal applications.
m  
pp1d 140231 Peak wave period This parameter represents the period of the most energetic ocean waves generated by local winds and associated with swell. The wave period is the average time it takes for two consecutive wave crests, on the surface of the ocean/sea, to pass through a fixed point.

The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). This parameter is calculated from the reciprocal of the frequency corresponding to the largest value (peak) of the frequency wave spectrum. The frequency wave spectrum is obtained by integrating the two-dimensional wave spectrum over all directions.

The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. This parameter takes account of both.
s  
mwp 140232 Mean wave period This parameter is the average time it takes for two consecutive wave crests, on the surface of the ocean/sea, to pass through a fixed point. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). This parameter is a mean over all frequencies and directions of the two-dimensional wave spectrum.

The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. This parameter takes account of both. See further documentation.

This parameter can be used to assess sea state and swell. For example, engineers use such wave information when designing structures in the open ocean, such as oil platforms, or in coastal applications.
s  
cdww 140233 Coefficient of drag with waves This parameter is the resistance that ocean waves exert on the atmosphere. It is sometimes also called a 'friction coefficient'.

It is calculated by the wave model as the ratio of the square of the friction velocity, to the square of the neutral wind speed at a height of 10 metres above the surface of the Earth.

The neutral wind is calculated from the surface stress and the corresponding roughness length by assuming that the air is neutrally stratified. The neutral wind is, by definition, in the direction of the surface stress. The size of the roughness length depends on the sea state.
dimensionless  
msqs 140244 Mean square slope of waves This parameter can be related analytically to the average slope of combined wind-sea and swell waves. It can also be expressed as a function of wind speed under some statistical assumptions. The higher the slope, the steeper the waves. This parameter indicates the roughness of the sea/ocean surface which affects the interaction between ocean and atmosphere. See further information.

The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). This parameter is derived statistically from the two-dimensional wave spectrum.
dimensionless  
wind 140245 10 metre wind speed This parameter is the horizontal speed of the 'neutral wind', at a height of ten metres above the surface of the Earth. The units of this parameter are metres per second.

The neutral wind is calculated from the surface stress and the corresponding roughness length by assuming that the air is neutrally stratified. The neutral wind is, by definition, in the direction of the surface stress. The size of the roughness length depends on sea state.

This parameter is the wind speed used to force the wave model, therefore it is only calculated over water bodies represented in the ocean wave model. It is interpolated from the atmospheric model's horizontal grid onto the horizontal grid used by the ocean wave model.
m s**-1  

V-iv: Monthly mean anomalies of individual ensemble members

Ranges Forecast time step Base times Resolution
1 to 7 month 6-hourly 00 UTC
  • 0.4° x 0.4° lat/long grid or any multiple thereof (global or sub-area)
  • 0.75° x 0.75° lat/long grid or any multiple thereof (global or sub-area)
  • On model (Gaussian) O320 (35 km) grid (global or sub-area)
  • Spectral components (T319) for upper-air fields (global area only)

 V-iv-a: Single level 

Short Name ID Long Name Description Units Additional information
z 129 Geopotential This parameter is the gravitational potential energy of a unit mass, at a particular location, relative to mean sea level. It is also the amount of work that would have to be done, against the force of gravity, to lift a unit mass to that location from mean sea level.

The geopotential height can be calculated by dividing the geopotential by the Earth's gravitational acceleration, g (=9.80665 m s-2). The geopotential height plays an important role in synoptic meteorology (analysis of weather patterns). Charts of geopotential height plotted at constant pressure levels (e.g., 300, 500 or 850 hPa) can be used to identify weather systems such as cyclones, anticyclones, troughs and ridges.

At the surface of the Earth, this parameter shows the variations in geopotential (height) of the surface, and is often referred to as the orography.
m**2 s**-2  
lsm 172 Land-sea mask This parameter is the proportion of land, as opposed to ocean or inland waters (lakes, reservoirs, rivers and coastal waters), in a grid box.
This parameter has values ranging between zero and one and is dimensionless.
In cycles of the ECMWF Integrated Forecasting System (IFS) from CY41R1 (introduced in May 2015) onwards, grid boxes where this parameter has a value above 0.5 can be comprised of a mixture of land and inland water but not ocean. Grid boxes with a value of 0.5 and below can only be comprised of a water surface. In the latter case, the lake cover is used to determine how much of the water surface is ocean or inland water.
In cycles of the IFS before CY41R1, grid boxes where this parameter has a value above 0.5 can only be comprised of land and those grid boxes with a value of 0.5 and below can only be comprised of ocean. In these older model cycles, there is no differentiation between ocean and inland water.
(0 - 1)  
lmlta 171024 Lake mix-layer temperature anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mixed-layer temperature of inland water bodies (lakes, reservoirs and rivers) or coastal waters is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

The mixed-layer temperature is the temperature of the uppermost layer of a lake that is well mixed. The ECMWF Integrated Forecasting System represents inland water bodies and coastal waters with two layers in the vertical, the mixed layer above and the thermocline below, where temperature changes with depth. The upper boundary of the thermocline is located at the mixed layer bottom, and the lower boundary of the thermocline at the lake bottom.

Mixing can occur when the density of the surface (and near-surface) water is greater than that of the water below. Mixing can also occur through the action of wind on the surface of the lake.

ECMWF implemented a lake model in May 2015 to represent the water temperature and lake ice of all the world's major inland water bodies in the Integrated Forecasting System (IFS). The IFS differentiates between (i) ocean water, handled by the ocean model, and (ii) inland water (lakes, reservoirs and rivers) and coastal waters handled by the lake parametrisation. Lake depth and surface area (or fractional cover) are kept constant in time.
K  
licda 171025 Lake ice depth anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the ice thickness on inland water bodies (lakes, reservoirs and rivers) and coastal waters is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

The ECMWF Integrated Forecasting System represents the formation and melting of ice on inland water bodies. A single ice layer is represented. Lake ice depth is the thickness of that ice layer.

ECMWF implemented a lake model in May 2015 to represent the water temperature and lake ice of all the world's major inland water bodies in the Integrated Forecasting System (IFS). The IFS differentiates between (i) ocean water, handled by the ocean model, and (ii) inland water (lakes, reservoirs and rivers) and coastal waters handled by the lake parametrisation. Lake depth and surface area (or fractional cover) are kept constant in time.
m  
sica 171031 Sea-ice cover anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the sea-ice cover is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

Sea-ice cover is the fraction of a grid box which is covered by sea-ice. Sea-ice can only occur in a grid box which is defined as ocean according to the land sea mask at the resolution being used. Sea-ice cover can also be known as sea-ice fraction or sea-ice concentration.

Sea-ice is frozen sea water which floats on the surface of the ocean. Sea-ice does not include ice which forms on land such as glaciers, icebergs and ice-sheets. It also excludes ice shelves which are anchored on land, but protrude out over the surface of the ocean. These phenomena are not modelled by the IFS.

Long-term monitoring of sea-ice cover is important for understanding climate change. Sea-ice cover also affects shipping routes through the polar regions.
(0 - 1)  
rsna 171033 Snow density anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the snow density is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

The ECMWF Integrated Forecast System represents snow as a single additional layer over the uppermost soil level. Snow density is assumed to be constant through the depth of the snow layer. Snow density changes with time due to the weight of snow and melt water in the snowpack.
kg m**-3  
ssta 171034 Sea surface temperature anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the temperature of sea water near the surface is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

Sea surface temperature (SST) is taken from various providers, who process the observational data in different ways. Each provider uses data from several different observational sources. For example, satellites measure SST in a layer a few microns thick in the uppermost mm of the ocean, drifting buoys measure SST at a depth of about 0.2-1.5m, whereas ships sample sea water down to about 10m, while the vessel is underway. Deeper measurements are not affected by changes that occur during a day, due to the rising and setting of the Sun (diurnal variations).

Sometimes SST is taken from a forecast made by coupling the NEMO ocean model to the ECMWF Integrated Forecasting System. In this case, the SST is the average temperature of the uppermost metre of the ocean and does exhibit diurnal variations.

See further SST documentation.
K  
swval1 171039 Volumetric soil water anomaly layer 1 An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the volumetric soil water is larger/smaller in layer 1 than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

Volumetric soil water is the volume of water in soil.

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:

Layer 1: 0 - 7cm

Layer 2: 7 - 28cm

Layer 3: 28 - 100cm

Layer 4: 100 - 289cm

The volumetric soil water is associated with the soil texture (or classification), soil depth, and the underlying groundwater level.
m**3 m**-3  
swval2 171040 Volumetric soil water anomaly layer 2 An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the volumetric soil water is larger/smaller in layer 2 than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

Volumetric soil water is the volume of water in soil.

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:

Layer 1: 0 - 7cm

Layer 2: 7 - 28cm

Layer 3: 28 - 100cm

Layer 4: 100 - 289cm

The volumetric soil water is associated with the soil texture (or classification), soil depth, and the underlying groundwater level.
m**3 m**-3  
swval3 171041 Volumetric soil water anomaly layer 3 An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the volumetric soil water is larger/smaller in layer 3 than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

Volumetric soil water is the volume of water in soil.

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:

Layer 1: 0 - 7cm

Layer 2: 7 - 28cm

Layer 3: 28 - 100cm

Layer 4: 100 - 289cm

The volumetric soil water is associated with the soil texture (or classification), soil depth, and the underlying groundwater level.
m**3 m**-3  
swval4 171042 Volumetric soil water anomaly layer 4 An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the volumetric soil water is larger/smaller in layer 4 than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

Volumetric soil water is the volume of water in soil.

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:

Layer 1: 0 - 7cm

Layer 2: 7 - 28cm

Layer 3: 28 - 100cm

Layer 4: 100 - 289cm

The volumetric soil water is associated with the soil texture (or classification), soil depth, and the underlying groundwater level.
m**3 m**-3  
10fga 171049 10 metre wind gust anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the 10 metre wind gust is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The WMO defines a wind gust as the maximum of the wind averaged over 3 second intervals. This duration is shorter than a model time step, and so the ECMWF Integrated Forecasting System deduces the magnitude of a gust within each time step from the time-step-averaged surface stress, surface friction, wind shear and stability. Then, the maximum wind gust is selected from the gusts at each time step during a particular time period which depends on the data extracted.

This parameter is calculated at a height of ten metres above the surface of the Earth.

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step.
m s**-1  
mx2t24a 171051 Maximum 2 metre temperature in the last 24 hours anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the maximum 2 metre temperature in the previous 24 hours is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

2m temperature is calculated by interpolating between the lowest model level and the Earth's surface, taking account of the atmospheric conditions. See further information.
K  
mn2t24a 171052 Minimum 2 metre temperature in the last 24 hours anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the minimum 2 metre temperature in the previous 24 hours is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

2m temperature is calculated by interpolating between the lowest model level and the Earth's surface, taking account of the atmospheric conditions. See further information.
K  
tclwa 171078 Total column liquid water anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the total amount of cloud liquid water (in a column extending from the surface of the Earth to the top of the atmosphere) is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

This parameter represents the area averaged value for a grid box.

Clouds contain a continuum of different sized water droplets and ice particles. The ECMWF Integrated Forecasting System (IFS) cloud scheme simplifies this to represent a number of discrete cloud droplets/particles including: cloud water droplets, raindrops, ice crystals and snow (aggregated ice crystals). The processes of droplet formation, conversion and aggregation are also highly simplified in the IFS.
kg m**-2  
tciwa 171079 Total column ice water anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the total amount of cloud ice (in a column extending from the surface of the Earth to the top of the atmosphere) is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information). This parameter does not include snow (i.e., precipitating ice).

This parameter represents the area averaged value for a grid box.

Clouds contain a continuum of different sized water droplets and ice particles. The ECMWF Integrated Forecasting System (IFS) cloud scheme simplifies this to represent a number of discrete cloud droplets/particles including: cloud water droplets, raindrops, ice crystals and snow (aggregated ice crystals). The processes of droplet formation, conversion and aggregation are also highly simplified in the IFS.
kg m**-2  
tcwva 171137 Total column water vapour anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the total water vapour (in a column extending from the surface of the Earth to the top of the atmosphere) is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

This parameter represents the area averaged value for a grid box.
kg m**-2  
stal1 171139 Soil temperature anomaly level 1 An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the soil temperature at level 1 (the middle of layer 1) is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:

Layer 1: 0 - 7cm

Layer 2: 7 - 28cm

Layer 3: 28 - 100cm

Layer 4: 100 - 289cm

Soil temperature is set at the middle of each layer, and heat transfer is calculated at the interfaces between them. It is assumed that there is no heat transfer out of the bottom of the lowest layer.

This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

See further information.
K  
sda 171141 Snow depth anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the snow depth is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

The ECMWF Integrated Forecast System represents snow as a single additional layer over the uppermost soil level. The snow may cover all or part of the grid box. Snow depth is the depth the water would have if the snow (from the snow-covered area of a grid box ) melted and was spread evenly over the whole grid box. Therefore, its units are metres of water equivalent.
m of water equivalent  
msla 171151 Mean sea level pressure anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean sea level pressure is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The mean sea level pressure is the pressure (force per unit area) of the atmosphere adjusted to the height of mean sea level. It is a measure of the weight that all the air in a column vertically above the area of Earth's surface would have at that point, if the point were located at the mean sea level. It is calculated over all surfaces - land, sea and in-land water.

Maps of mean sea level pressure are used to identify the locations of low and high pressure systems, often referred to as cyclones and anticyclones. Contours of mean sea level pressure also indicate the strength of the wind. Tightly packed contours show stronger winds.

The units of this parameter are pascals (Pa). Mean sea level pressure is often measured in hPa and sometimes is presented in the old units of millibars, mb (1 hPa = 1 mb = 100 Pa).
Pa  
tcca 171164 Total cloud cover anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that total cloud cover is larger/smaller than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Total cloud cover is the proportion of a model grid box covered by cloud. Total cloud cover is a single level field calculated from the cloud occurring at different model levels through the atmosphere. Assumptions are made about the degree of overlap/randomness between the horizontal positioning of clouds at different heights.
(0 - 1)  
10ua 171165 10 metre U wind component anomaly An anomaly is a difference from a defined long-term average. A positive anomaly indicates that the wind is more eastward (or less westward) than average. A negative anomaly indicates that the wind is more westward (or less eastward) than average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The 10 metre U wind component is the eastward component of the 10 m wind. It is the horizontal speed of air moving towards the east, at a height of ten metres above the surface of the Earth, in metres per second.

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step.
m s**-1  
10va 171166 10 metre V wind component anomaly An anomaly is a difference from a defined long-term average. A positive anomaly indicates that the wind is more northward (or less southward) than average. A negative anomaly indicates that the wind is more southward (or less northward) than average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The 10 metre V wind component is the northward component of the 10 m wind. It is the horizontal speed of air moving towards the north, at a height of ten metres above the surface of the Earth, in metres per second.

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step.
m s**-1  
2ta 171167 2 metre temperature anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the 2 metre temperature is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

2m temperature is calculated by interpolating between the lowest model level and the Earth's surface, taking account of the atmospheric conditions. See further information.
K  
2da 171168 2 metre dewpoint temperature anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the 2 metre dew point temperature is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Dew point temperature is the temperature to which the air would have to be cooled for saturation to occur. It is a measure of the humidity of the air. Combined with temperature and pressure, it can be used to calculate the relative humidity.

2m dew point temperature is calculated by interpolating between the lowest model level and the Earth's surface, taking account of the atmospheric conditions.See further information.
K  
stal2 171170 Soil temperature anomaly level 2 An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the soil temperature at level 2 (the middle of layer 2) is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:

Layer 1: 0 - 7cm

Layer 2: 7 - 28cm

Layer 3: 28 - 100cm

Layer 4: 100 - 289cm

Soil temperature is set at the middle of each layer, and heat transfer is calculated at the interfaces between them. It is assumed that there is no heat transfer out of the bottom of the lowest layer.

This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

See further information.
K  
stal3 171183 Soil temperature anomaly level 3 An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the soil temperature at level 3 (the middle of layer 3) is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:

Layer 1: 0 - 7cm

Layer 2: 7 - 28cm

Layer 3: 28 - 100cm

Layer 4: 100 - 289cm

Soil temperature is set at the middle of each layer, and heat transfer is calculated at the interfaces between them. It is assumed that there is no heat transfer out of the bottom of the lowest layer.

This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

See further information.
K  
lcca 171186 Low cloud cover anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that low cloud cover is larger/smaller than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Low cloud cover is the proportion of a model grid box covered by cloud occurring in the lower levels of the troposphere. Low cloud is a single level field calculated from cloud occurring on model levels with a pressure greater than 0.8 times the surface pressure. So, if the surface pressure is 1000 hPa (hectopascal), low cloud would be calculated using levels with a pressure greater than 800 hPa (below approximately 2 km (assuming a 'standard atmosphere')).

The low cloud cover parameter is calculated from cloud cover for the appropriate model levels as described above. Assumptions are made about the degree of overlap/randomness between the horizontal positioning of clouds in different model levels.
(0 - 1)  
tco3a 171206 Total column ozone anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that total column ozone is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Total column ozone is the total amount of ozone in a column of air extending from the surface of the Earth to the top of the (model) atmosphere. This parameter can also be referred to as total ozone, or vertically integrated ozone. The values are dominated by ozone within the stratosphere.

In the ECMWF Integrated Forecasting System (IFS), there is a simplified representation of ozone chemistry (including representation of the chemistry which has caused the ozone hole). Ozone is also transported around in the atmosphere through the motion of air. See further documentation.

Naturally occurring ozone in the stratosphere helps protect organisms at the surface of the Earth from the harmful effects of ultraviolet (UV) radiation from the Sun. Ozone near the surface, often produced because of pollution, is harmful to organisms.

In the IFS, the units for total ozone are kilograms per square metre, but before 12/06/2001 dobson units were used. Dobson units (DU) are still used extensively for total column ozone. 1 DU = 2.1415E-5 kg m-2.
kg m**-2  
10sia 171207 10 metre wind speed anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the 10 metre wind speed is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The 10 metre wind speed is the horizontal speed of the wind, or movement of air, at a height of ten metres above the surface of the Earth.

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step.
m s**-1  
iewsa 171229 Instantaneous X surface stress anomaly An anomaly is a difference from a defined long-term average. A positive anomaly indicates that the surface stress is more eastward (or less westward) than average. A negative anomaly indicates that the surface stress is more westward (or less eastward) than the average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Air flowing over a surface exerts a stress that transfers momentum to the surface and slows the wind. The instantaneous X surface stress is the stress on the Earth's surface at the specified time in the eastward direction due to both the turbulent interactions between the atmosphere and the surface, and to turbulent orographic form drag.

The turbulent interactions between the atmosphere and the surface are due to the roughness of the surface.

The turbulent orographic form drag is the stress due to the valleys, hills and mountains on horizontal scales below 5km being derived from land surface data at about 1 km resolution. See further information.
N m**-2  
inssa 171230 Instantaneous Y surface stress anomaly An anomaly is a difference from a defined long-term average. A positive anomaly indicates that the surface stress is more northward (or less southward) than average. A negative anomaly indicates that the surface stress is more southward (or less northward) than the average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Air flowing over a surface exerts a stress that transfers momentum to the surface and slows the wind. The instantaneous Y surface stress is the stress on the Earth's surface at the specified time in the northward direction due to both the turbulent interactions between the atmosphere and the surface, and to turbulent orographic form drag.

The turbulent interactions between the atmosphere and the surface are due to the roughness of the surface.

The turbulent orographic form drag is the stress due to the valleys, hills and mountains on horizontal scales below 5km being derived from land surface data at about 1 km resolution. See further information.
N m**-2  
stal4 171236 Soil temperature level 4 anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the soil temperature at level 4 (the middle of layer 4) is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:

Layer 1: 0 - 7cm

Layer 2: 7 - 28cm

Layer 3: 28 - 100cm

Layer 4: 100 - 289cm

Soil temperature is set at the middle of each layer, and heat transfer is calculated at the interfaces between them. It is assumed that there is no heat transfer out of the bottom of the lowest layer.

This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

See further information.
K  
fala 171243 Forecast albedo anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the forecast albedo is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The forecast albedo is a measure of the reflectivity of the Earth's surface. It is the fraction of solar (shortwave) radiation reflected by Earth's surface, across the solar spectrum, for both direct and diffuse radiation. Typically, snow and ice have high reflectivity with albedo values of 0.8 and above, land has intermediate values between about 0.1 and 0.4 and the ocean has low values of 0.1 or less. See further documentation.

In the ECMWF Integrated Forecasting System (IFS), the model only modifies albedo values over water, ice and snow, elsewhere a background climatological albedo is used.
(0 - 1)  
msrora 173008 Mean surface runoff rate anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean surface runoff rate is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The mean surface runoff rate is the amount of water from rainfall or melting snow that is not absorbed by the soil and drains away over the surface. Water may also drain away under the ground. It is the accumulated amount of water, divided by the length of the accumulation period, which depends on the data extracted.

This quantity represents the depth this water would have if it were spread evenly over the grid box.

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step
m of water equivalent s**-1  
mssrora 173009 Mean sub-surface runoff rate anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean sub-surface runoff rate is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The mean sub-surface runoff rate is the amount of water deep in the soil that drains away under the ground. Water may also drain away over the surface. It is the accumulated amount of water, divided by the length of the accumulation period, which depends on the data extracted.

This quantity represents the depth this water would have if it were spread evenly over the grid box.

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step
m of water equivalent s**-1  
lspara 173142 Stratiform precipitation (Large-scale precipitation) anomalous rate of accumulation An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean large-scale precipitation rate is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Mean large-scale precipitation rate is accumulated precipitation divided by the length of the accumulation period, which depends on the data extracted.

For this parameter, precipitation is made up of rain and snow that falls to the Earth's surface, generated by the cloud scheme in the ECMWF Integrated Forecasting System (IFS). The cloud scheme represents the formation and dissipation of clouds and large-scale precipitation due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly by the IFS at spatial scales of a grid box or larger. Precipitation can also be due to convection generated by the convection scheme in the IFS. The convection scheme represents convection at spatial scales smaller than the grid box. See further information.Precipitation parameters do not include fog, dew or the precipitation that evaporates in the atmosphere before it lands at the surface of the Earth.

The units include depth in metres of water equivalent. This is the depth the water would have if it were spread evenly over the grid box.

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step.
m s**-1  
mcpra 173143 Mean convective precipitation rate anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean convective precipitation rate is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

Mean convective precipitation rate is accumulated precipitation divided by the length the accumulation period, which depends on the data extracted.

For this parameter, precipitation is rain and snow that falls to the Earth's surface, generated by the convection scheme in the ECMWF Integrated Forecasting System (IFS). The convection scheme represents convection at spatial scales smaller than the grid box. Total precipitation is made up of convective and large-scale precipitation. Large-scale precipitation is generated by the cloud scheme in the IFS. The cloud scheme represents the formation and dissipation of clouds and large-scale precipitation due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly by the IFS at spatial scales of a grid box or larger. See further information.

The units include depth, in metres of water equivalent. This is the depth the water would have if it were spread evenly over the grid box. Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step .
m s**-1  
sfara 173144 Snowfall (convective + stratiform) anomalous rate of accumulation An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean snowfall rate is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

The mean snowfall rate is the accumulated snowfall divided by the length of the accumulation period, which depends on the data extracted.

Snowfall is the sum of large-scale snowfall and convective snowfall. Large-scale snowfall is generated by the cloud scheme in the ECMWF Integrated Forecast System. The cloud scheme represents the formation and dissipation of clouds and large-scale snowfall due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly by the IFS at spatial scales of a grid box or larger. Convective snowfall is generated by the convection scheme in the IFS. The convection scheme represents convection at spatial scales smaller than the grid box. See further information.

The units are depth of water equivalent in metres which falls per second (i.e., the depth the melted snow would have if it were spread evenly over the grid box ).

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step.
m of water equivalent s**-1  
sshfara 173146 Surface sensible heat flux anomalous rate of accumulation An anomaly is a difference from a defined long-term average. Since the ECMWF convention for vertical fluxes is positive downwards, a positive anomaly means either a larger downward mean surface sensible heat flux or a smaller upward flux, compared with the long-term average. A negative anomaly means either a smaller downward flux or a larger upward flux. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Surface sensible heat flux is the transfer of heat between the Earth's surface and the atmosphere through the effects of turbulent air motion (but excluding any heat transfer resulting from condensation or evaporation). The mean flux is the accumulated flux divided by the length of the accumulation period, which depends on the data extracted.
J m**-2  
slhfara 173147 Surface latent heat flux anomalous rate of accumulation An anomaly is a difference from a defined long-term average. Since the ECMWF convention for vertical fluxes is positive downwards, a positive anomaly means either a larger downward mean surface latent heat flux or a smaller upward flux, compared with the long-term average. A negative anomaly means either a smaller downward flux or a larger upward flux. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The surface latent heat flux is the transfer of latent heat (resulting from evaporation, condensation and other moisture phase changes) between the Earth's surface and the atmosphere through the effects of turbulent air motion. Evaporation from the Earth's surface represents a transfer of energy from the surface to the atmosphere. The mean latent heat flux is the accumulated flux divided by the length of the accumulation period, which depends on the data extracted.
J m**-2  
ssrdara 173169 Surface solar radiation downwards anomalous rate of accumulation   J m**-2  
strdara 173175 Surface thermal radiation downwards anomalous rate of accumulation An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean flux of surface thermal radiation downwards is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Surface thermal radiation downwards is the amount of thermal (also known as longwave or terrestrial) radiation emitted by the atmosphere and clouds that reaches the Earth's surface. It is the amount of radiation passing through a horizontal plane. The mean flux is the accumulated flux divided by the length of the accumulation period, which depends on the data extracted.

The ECMWF convention for vertical fluxes is positive downwards.
J m**-2  
ssrara 173176 Surface solar radiation anomalous rate of accumulation An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean net surface solar radiation flux is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The net surface solar radiation flux is the amount of solar radiation (also known as shortwave radiation) reaching the surface of the Earth (both direct and diffuse) minus the amount reflected by the Earth's surface (which is governed by the albedo). It is the amount of radiation passing through a horizontal plane, not a plane perpendicular to the direction of the Sun. The mean flux is the accumulated flux divided by the length of the accumulation period, which depends on the data extracted.

The ECMWF convention for vertical fluxes is positive downwards.
J m**-2  
strara 173177 Surface thermal radiation anomalous rate of accumulation An anomaly is a difference from a defined long-term average. Since the ECMWF convention for vertical fluxes is positive downwards, a positive anomaly means either a larger downward mean net surface thermal radiation flux or a smaller upward flux, compared with the long-term average. A negative anomaly means either a smaller downward flux or a larger upward flux. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Thermal radiation (also known as longwave or terrestrial radiation) refers to radiation emitted by the atmosphere, clouds and the surface of the Earth. The net surface thermal radiation flux is the difference between downward and upward thermal radiation at the surface of the Earth. It is the amount of radiation passing through a horizontal plane.

The atmosphere and clouds emit thermal radiation in all directions, some of which reaches the surface as downward thermal radiation. The upward thermal radiation at the surface consists of thermal radiation emitted by the surface plus the fraction of downwards thermal radiation reflected upward by the surface. See further documentation

The mean flux is the accumulated flux divided by the length of the accumulation period, which depends on the data extracted.
J m**-2  
tsrara 173178 Top solar radiation anomalous rate of accumulation An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean net flux of solar radiation at the top of the atmosphere is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The net flux of solar radiation (also known as shortwave radiation) at the top of the atmosphere is the incoming solar radiation minus the outgoing solar radiation. It is the amount of radiation passing through a horizontal plane. The incoming solar radiation is the amount received from the Sun. The outgoing solar radiation is the amount reflected and scattered by the Earth's atmosphere and surface. See further documentation.

The mean flux is the accumulated flux divided by the length of the accumulation period, which depends on the data extracted.

The ECMWF convention for vertical fluxes is positive downwards.
J m**-2  
ttrara 173179 Top thermal radiation anomalous rate of accumulation An anomaly is a difference from a defined long-term average. The ECMWF convention for vertical fluxes is positive downwards and the mean flux of thermal radiation at the top of the atmosphere can only be upwards (i.e., negative). Therefore, a positive anomaly means a smaller upward flux of thermal radiation and a negative anomaly means a larger upward flux, compared with the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The mean flux of thermal radiation (also known as longwave or terrestrial) is the thermal radiation emitted to space at the top of the atmosphere. See further documentation. The mean flux is the accumulated flux divided by the length of the accumulation period, which depends on the data extracted.

The thermal radiation emitted to space at the top of the atmosphere is commonly known as the Outgoing Longwave Radiation (OLR) (but taking a flux from the atmosphere to space as positive).
J m**-2  
ewssara 173180 East-West surface stress anomalous rate of accumulation An anomaly is a difference from a defined long-term average. A positive anomaly indicates that the mean East-West surface stress is more eastward (or less westward) than average. A negative anomaly indicates that the mean East-West surface stress is more westward (or less eastward) than the average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Air flowing over a surface exerts a stress that transfers momentum to the surface and slows the wind. The mean East-West surface stress is the accumulated eastward surface stress divided by the length of the accumulation period, which depends on the data extracted.

The East-West surface stress is the stress on the Earth's surface in the eastward direction due to both the turbulent interactions between the atmosphere and the surface, and to turbulent orographic form drag. The turbulent interactions between the atmosphere and the surface are due to the roughness of the surface. The turbulent orographic form drag is the stress due to the valleys, hills and mountains on horizontal scales below 5km being derived from land surface data at about 1 km resolution. See further information.
N m**-2  
nsssara 173181 North-South surface stress anomalous rate of accumulation An anomaly is a difference from a defined long-term average. A positive anomaly indicates that the mean North-South surface stress is more northward (or less southward) than average. A negative anomaly indicates that the mean North-South surface stress is more southward (or less northward) than the average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Air flowing over a surface exerts a stress that transfers momentum to the surface and slows the wind. The mean North-South surface stress is the accumulated northward surface stress divided by the length of the accumulation period, which depends on the data extracted.

The North-South surface stress is the stress on the Earth's surface in the northward direction due to both the turbulent interactions between the atmosphere and the surface, and to turbulent orographic form drag. The turbulent interactions between the atmosphere and the surface are due to the roughness of the surface. The turbulent orographic form drag is the stress due to the valleys, hills and mountains on horizontal scales below 5km being derived from land surface data at about 1 km resolution. See further information.
N m**-2  
evara 173182 Evaporation anomalous rate of accumulation An anomaly is a difference from a defined long-term average. The ECMWF Integrated Forecasting System convention is that downward fluxes are positive. Therefore a positive anomaly means either a larger downward mean evaporation flux (more condensation) or a smaller upward flux (less evaporation), compared with the long-term average. A negative anomaly means either a smaller downward flux or a larger upward flux. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Evaporation is the amount of water that has evaporated from the Earth's surface, including a simplified representation of transpiration (from vegetation), into vapour in the air above.The mean evaporation rate is the accumulated evaporation divided by the length of the accumulation period, which depends on the data extracted.
m of water s**-1  
sundara 173189 Sunshine duration anomalous rate of accumulation An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean sunshine duration rate is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The mean sunshine duration rate is the accumulated sunshine duration divided by the length of the accumulation period, which depends on the data extracted.

The sunshine duration is the length of time in which the direct solar (shortwave) radiation at the Earth's surface, falling on a plane perpendicular to the direction of the Sun, is greater than or equal to 120 W m-2.

The minimum solar intensity level of 120 W m-2 is defined by the World Meteorological Organisation and is consistent with observed values of sunshine duration from a Campbell-Stokes recorder (sometimes called a Stokes sphere) that can only measure moderately intense sunlight and brighter.
dimensionless  
roara 173205 Runoff anomalous rate of accumulation An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean runoff rate is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The mean runoff rate is the total amount of water from rainfall, melting snow, or deep in the soil, that drains away over the surface and under the ground. It is the accumulated amount of water, divided by the length of the accumulation period, which depends on the data extracted.

This quantity represents the depth this water would have if it were spread evenly over the grid box.

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step.
m s**-1  
soiara 173212 Solar insolation anomalous rate of accumulation An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean solar insolation is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Solar insolation is the incoming radiation from the Sun (also known as solar or shortwave radiation) at the top of the atmosphere (TOA). It is the amount of radiation passing through a horizontal plane, not a plane perpendicular to the direction of the Sun.

Solar insolation has a diurnal cycle (as it is defined into a horizontal plane and not a plane perpendicular to the Sun), as well as an annual cycle due to the change in Sun-Earth distance, and the approximately 11-year solar cycle. Solar insolation at the TOA has experienced no absorption, scattering or reflection within the atmosphere (e.g., from clouds, water vapour, ozone, trace gases and aerosol).

The mean flux is the accumulated flux divided by the length of the accumulation period, which depends on the data extracted. The ECMWF convention for vertical fluxes is positive downwards.
W m**-2 s**-1  
tpara 173228 Total precipitation anomalous rate of accumulation An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the mean precipitation rate is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The mean precipitation rate is the accumulated precipitation divided by the length of the accumulation period, which depends on the data extracted.

In the ECMWF Integrated Forecasting System (IFS), total precipitation is rain and snow that falls to the Earth's surface. It is the sum of large-scale precipitation and convective precipitation. Large-scale precipitation is generated by the cloud scheme in the IFS. The cloud scheme represents the formation and dissipation of clouds and large-scale precipitation due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly by the IFS at spatial scales of a grid box or larger. Convective precipitation is generated by the convection scheme in the IFS. The convection scheme represents convection at spatial scales smaller than the grid box. See further information. Precipitation parameters do not include fog, dew or the precipitation that evaporates in the atmosphere before it lands at the surface of the Earth.

The units are depth of water equivalent in metres which falls per second. It is the depth the water would have if it were spread evenly over the grid box.

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box and model time step .
m s**-1  

V-iv-b: Pressure levels

Available at 1000, 925, 850, 700, 500, 400, 300, 200 hPa unless otherwise specified.

Short Name ID Long Name Description Units Additional information
za 171129 Geopotential anomaly   m**2 s**-2  
ta 171130 Temperature anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that temperature is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

This parameter is available on multiple levels through the atmosphere.
K  
ua 171131 U component of wind anomaly An anomaly is a difference from a defined long-term average. A positive anomaly indicates that the wind is more eastward (or less westward) than average. A negative anomaly indicates that the wind is more westward (or less eastward) than average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The U component of wind is the eastward component of the wind. It is the horizontal speed of air moving towards the east, in metres per second. A negative U component of wind thus indicates air movement towards the west.
m s**-1  
va 171132 V component of wind anomaly An anomaly is a difference from a defined long-term average. A positive anomaly indicates that the wind is more northward (or less southward) than average. A negative anomaly indicates that the wind is more southward (or less northward) than average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The V component of wind is the northward component of the wind. It is the horizontal speed of air moving towards the north, in metres per second. A negative V component of wind thus indicates air movement towards the south.
m s**-1  
qa 171133 Specific humidity anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the specific humidity is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information ).

Specific humidity is the mass of water vapour per kilogram of moist air. The total mass of moist air is the sum of the dry air, water vapour, cloud liquid, cloud ice, rain and falling snow.
kg kg**-1  
voa 171138 Relative vorticity anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the relative vorticity is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Relative vorticity is a measure of the rotation of air in the horizontal, around a vertical axis, relative to a fixed point on the surface of the Earth.

On the scale of weather systems, low pressure systems (weather features that can include rain) are associated with anticlockwise rotation (in the northern hemisphere), and high pressure systems (weather features that bring light or still winds) are associated with clockwise rotation.

Adding the effect of rotation of the Earth, the Coriolis parameter, to the relative vorticity produces the absolute vorticity.
s**-1  
da 171155 Relative divergence anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that the relative divergence is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

The relative divergence, also called simply the divergence, is the horizontal divergence of velocity. It is the rate at which air is spreading out horizontally from a point, per square metre. This parameter is positive for air that is spreading out, or diverging, and negative for the opposite, for air that is concentrating, or converging (convergence).
s**-1  
gha 171156 Height anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that geopotential height is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Geopotential height is a measure of the height of a point in the atmosphere in relation to its potential energy. It is calculated by dividing the geopotential by the Earth's mean gravitational acceleration, g (=9.80665 m s-2). The geopotential is the gravitational potential energy of a unit mass, at a particular location, relative to mean sea level. Geopotential is also the amount of work that would have to be done, against the force of gravity, to lift a unit mass to that location from mean sea level.

Geopotential height plays an important role in synoptic meteorology (analysis of weather patterns). Charts of geopotential height plotted at constant pressure levels (e.g., 300, 500 or 850 hPa) can be used to identify weather systems such as cyclones, anticyclones, troughs and ridges.

The units of this parameter are geopotential metres. A geopotential metre is 2% shorter than a dynamic metre (also called a geodynamic metre).
m  
o3a 171203 Ozone mass mixing ratio anomaly An anomaly is a difference from a defined long-term average. Positive/negative values of this parameter indicate that ozone mass mixing ratio is higher/lower than the long-term average. The long-term average is typically derived from several decades of model data and will vary with location and time of year (see further information).

Ozone mass mixing ratio is the mass of ozone per kilogram of air.

In the ECMWF Integrated Forecasting System (IFS), there is a simplified representation of ozone chemistry (including representation of the chemistry which has caused the ozone hole). Ozone is also transported around in the atmosphere through the motion of air. See further documentation.

Naturally occurring ozone in the stratosphere helps protect organisms at the surface of the Earth from the harmful effects of ultraviolet (UV) radiation from the Sun. Ozone near the surface, often produced because of pollution, is harmful to organisms.

Most of the IFS chemical species are archived as mass mixing ratios [kg kg-1]. This link explains how to convert to concentration in terms of mass per unit volume.
kg kg**-1  

V-v: Individual forecast runs

Ranges Forecast time step Base times Resolution
T+0h to T+5160h 6-hourly 00 UTC
  • 0.4° x 0.4° lat/long grid or any multiple thereof (global or sub-area)
  • 0.75° x 0.75° lat/long grid or any multiple thereof (global or sub-area)
  • On model (Gaussian) O320 (35 km) grid (global or sub-area)
  • Spectral components (T319) for upper-air fields (global area only)

V-v-a: Single level - 6-hourly 

Short Name ID Long Name Description Units Additional information
sst 34 Sea surface temperature This parameter is the temperature of sea water near the surface.

This parameter is taken from various providers, who process the observational data in different ways. Each provider uses data from several different observational sources. For example, satellites measure sea surface temperature (SST) in a layer a few microns thick in the uppermost mm of the ocean, drifting buoys measure SST at a depth of about 0.2-1.5m, whereas ships sample sea water down to about 10m, while the vessel is underway. Deeper measurements are not affected by changes that occur during a day, due to the rising and setting of the Sun (diurnal variations).

Sometimes this parameter is taken from a forecast made by coupling the NEMO ocean model to the ECMWF Integrated Forecasting System. In this case, the SST is the average temperature of the uppermost metre of the ocean and does exhibit diurnal variations.

See further documentation .

This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.
K  
stl1 139 Soil temperature level 1 This parameter is the temperature of the soil at level 1 (in the middle of layer 1).

The ECMWF Integrated Forecasting System (IFS) has a four-layer representation of soil, where the surface is at 0cm:

Layer 1: 0 - 7cm
Layer 2: 7 - 28cm
Layer 3: 28 - 100cm
Layer 4: 100 - 289cm

Soil temperature is set at the middle of each layer, and heat transfer is calculated at the interfaces between them. It is assumed that there is no heat transfer out of the bottom of the lowest layer.

This parameter has units of Kelvin (K). Temperature measured in Kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

See further information.
K  
sf 144 Snowfall This parameter is the accumulated snow that falls to the Earth's surface. It is the sum of large-scale snowfall and convective snowfall. Large-scale snowfall is generated by the cloud scheme in the ECMWF Integrated Forecasting System (IFS). The cloud scheme represents the formation and dissipation of clouds and large-scale precipitation due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly by the IFS at spatial scales of the grid box or larger. Convective snowfall is generated by the convection scheme in the IFS, which represents convection at spatial scales smaller than the grid box. See further information.

This parameter is the total amount of water accumulated over a particular time period which depends on the data extracted. The units of this parameter are depth in metres of water equivalent. It is the depth the water would have if it were spread evenly over the grid box.

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box.
m of water equivalent  
msl 151 Mean sea level pressure This parameter is the pressure (force per unit area) of the atmosphere adjusted to the height of mean sea level.

It is a measure of the weight that all the air in a column vertically above the area of Earth's surface would have at that point, if the point were located at the mean sea level. It is calculated over all surfaces - land, sea and in-land water.

Maps of mean sea level pressure are used to identify the locations of low and high pressure systems, often referred to as cyclones and anticyclones. Contours of mean sea level pressure also indicate the strength of the wind. Tightly packed contours show stronger winds.

The units of this parameter are pascals (Pa). Mean sea level pressure is often measured in hPa and sometimes is presented in the old units of millibars, mb (1 hPa = 1 mb = 100 Pa).
Pa  
tcc 164 Total cloud cover This parameter is the proportion of a grid box covered by cloud. Total cloud cover is a single level field calculated from the cloud occurring at different model levels through the atmosphere. Assumptions are made about the degree of overlap/randomness between clouds at different heights.

Cloud fractions vary from 0 to 1.
(0 - 1)  
10u 165 10 metre U wind component This parameter is the eastward component of the 10m wind. It is the horizontal speed of air moving towards the east, at a height of ten metres above the surface of the Earth, in metres per second.

Care should be taken when comparing this parameter with observations, because wind observations vary on small space and time scales and are affected by the local terrain, vegetation and buildings that are represented only on average in the ECMWF Integrated Forecasting System.

This parameter can be combined with the V component of 10m wind to give the speed and direction of the horizontal 10m wind.
m s**-1  
10v 166 10 metre V wind component This parameter is the northward component of the 10m wind. It is the horizontal speed of air moving towards the north, at a height of ten metres above the surface of the Earth, in metres per second.

Care should be taken when comparing this parameter with observations, because wind observations vary on small space and time scales and are affected by the local terrain, vegetation and buildings that are represented only on average in the ECMWF Integrated Forecasting System.

This parameter can be combined with the U component of 10m wind to give the speed and direction of the horizontal 10m wind.
m s**-1  
2t 167 2 metre temperature This parameter is the temperature of air at 2m above the surface of land, sea or in-land waters.

2m temperature is calculated by interpolating between the lowest model level and the Earth's surface, taking account of the atmospheric conditions. See further information .

This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.
K  
2d 168 2 metre dewpoint temperature This parameter is the temperature to which the air, at 2 metres above the surface of the Earth, would have to be cooled for saturation to occur.

It is a measure of the humidity of the air. Combined with temperature and pressure, it can be used to calculate the relative humidity.

2m dew point temperature is calculated by interpolating between the lowest model level and the Earth's surface, taking account of the atmospheric conditions. See further information.This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.
K  
ssrd 169 Surface solar radiation downwards This parameter is the amount of solar radiation (also known as shortwave radiation) that reaches a horizontal plane at the surface of the Earth. This parameter comprises both direct and diffuse solar radiation.

Radiation from the Sun (solar, or shortwave, radiation) is partly reflected back to space by clouds and particles in the atmosphere (aerosols) and some of it is absorbed. The rest is incident on the Earth's surface (represented by this parameter). See further documentation.

To a reasonably good approximation, this parameter is the model equivalent of what would be measured by a pyranometer (an instrument used for measuring solar radiation) at the surface. However, care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box.

This parameter is accumulated over a particular time period which depends on the data extracted. The units are joules per square metre (J m-2). To convert to watts per square metre (W m-2), the accumulated values should be divided by the accumulation period expressed in seconds. The ECMWF convention for vertical fluxes is positive downwards.
J m**-2  
strd 175 Surface thermal radiation downwards This parameter is the amount of thermal (also known as longwave or terrestrial) radiation emitted by the atmosphere and clouds that reaches a horizontal plane at the surface of the Earth.

The surface of the Earth emits thermal radiation, some of which is absorbed by the atmosphere and clouds. The atmosphere and clouds likewise emit thermal radiation in all directions, some of which reaches the surface (represented by this parameter). See further documentation.

This parameter is accumulated over a particular time period which depends on the data extracted. The units are joules per square metre (J m-2). To convert to watts per square metre (W m-2), the accumulated values should be divided by the accumulation period expressed in seconds. The ECMWF convention for vertical fluxes is positive downwards.
J m**-2  
tp 228 Total precipitation This parameter is the accumulated liquid and frozen water, comprising rain and snow, that falls to the Earth's surface. It is the sum of large-scale precipitation and convective precipitation. Large-scale precipitation is generated by the cloud scheme in the ECMWF Integrated Forecasting System (IFS). The cloud scheme represents the formation and dissipation of clouds and large-scale precipitation due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly by the IFS at spatial scales of the grid box or larger. Convective precipitation is generated by the convection scheme in the IFS, which represents convection at spatial scales smaller than the grid box. See further information. This parameter does not include fog, dew or the precipitation that evaporates in the atmosphere before it lands at the surface of the Earth.

This parameter is the total amount of water accumulated over a particular time period which depends on the data extracted. The units of this parameter are depth in metres of water equivalent. It is the depth the water would have if it were spread evenly over the grid box.

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box.
m  
iews 229 Instantaneous eastward turbulent surface stress Air flowing over a surface exerts a stress that transfers momentum to the surface and slows the wind. This parameter is the stress on the Earth's surface at the specified time in the eastward direction due to both the turbulent interactions between the atmosphere and the surface, and to turbulent orographic form drag.

The turbulent interactions between the atmosphere and the surface are due to the roughness of the surface.

The turbulent orographic form drag is the stress due to the valleys, hills and mountains on horizontal scales below 5km being derived from land surface data at about 1 km resolution. See further information.

Positive (negative) values denote stress in the eastward (westward) direction.
N m**-2  
inss 230 Instantaneous northward turbulent surface stress Air flowing over a surface exerts a stress that transfers momentum to the surface and slows the wind. This parameter is the stress on the Earth's surface at the specified time in the northward direction due to both the turbulent interactions between the atmosphere and the surface, and to turbulent orographic form drag.

The turbulent interactions between the atmosphere and the surface are due to the roughness of the surface.

The turbulent orographic form drag is the stress due to the valleys, hills and mountains on horizontal scales below 5km being derived from land surface data at about 1 km resolution. See further information.

Positive (negative) values denote stress in the northward (southward) direction.
N m**-2  

V-v-b: Single level 24-hourly

Short Name ID Long Name Description Units Additional information
sro 8 Surface runoff Some water from rainfall, melting snow, or deep in the soil, stays stored in the soil. Otherwise, the water drains away, either over the surface (surface runoff), or under the ground (sub-surface runoff) and the sum of these two is simply called 'runoff'. This parameter is the total amount of water accumulated over a particular time period which depends on the data extracted.The units of runoff are depth in metres. This is the depth the water would have if it were spread evenly over the grid box. Care should be taken when comparing model parameters with observations, because observations are often local to a particular point rather than averaged over a grid square area. Observations are also often taken in different units, such as mm/day, rather than the accumulated metres produced here.

Runoff is a measure of the availability of water in the soil, and can, for example, be used as an indicator of drought or flood. More information about how runoff is calculated is given in the IFS Physical Processes documentation.
m  
ssro 9 Sub-surface runoff Some water from rainfall, melting snow, or deep in the soil, stays stored in the soil. Otherwise, the water drains away, either over the surface (surface runoff), or under the ground (sub-surface runoff) and the sum of these two is simply called 'runoff'. This parameter is the total amount of water accumulated over a particular time period which depends on the data extracted.The units of runoff are depth in metres. This is the depth the water would have if it were spread evenly over the grid box. Care should be taken when comparing model parameters with observations, because observations are often local to a particular point rather than averaged over a grid square area. Observations are also often taken in different units, such as mm/day, rather than the accumulated metres produced here.

Runoff is a measure of the availability of water in the soil, and can, for example, be used as an indicator of drought or flood. More information about how runoff is calculated is given in the IFS Physical Processes documentation.
m  
cl 26 Lake cover This parameter is the proportion of a grid box covered by inland water bodies (lakes, reservoirs, rivers) and coastal waters. Values vary between 0: no inland or coastal water body, and 1: grid box is fully covered with inland or coastal water body. This field is specified from observations and is constant in time.

ECMWF implemented a lake model in May 2015 to represent the water temperature and lake ice of all the world's major inland water bodies in the Integrated Forecasting System (IFS). The IFS differentiates between (i) ocean water, handled by the ocean model, and (ii) inland water (lakes, reservoirs and rivers) and coastal waters handled by the lake parametrisation. Lake depth and surface area (or fractional cover) are kept constant in time.
(0 - 1)  
ci 31 Sea ice area fraction This parameter is the fraction of a grid box which is covered by sea ice. Sea ice can only occur in a grid box which includes ocean or inland water according to the land sea mask and lake cover, at the resolution being used. This parameter can be known as sea-ice (area) fraction, sea-ice concentration and more generally as sea-ice cover.

Coupled atmosphere ocean simulations of the ECMWF Integrated Forecasting System (IFS) predict the formation and melting of sea ice. Otherwise, in analyses and atmosphere only simulations, sea ice is derived from observations, but the model does take account of the way that sea ice alters the interaction between the atmosphere and ocean.

Sea ice is frozen sea water which floats on the surface of the ocean. Sea ice does not include ice which forms on land such as glaciers, icebergs and ice-sheets. It also excludes ice shelves which are anchored on land, but protrude out over the surface of the ocean. These phenomena are not modelled by the IFS.

Long-term monitoring of sea ice is important for understanding climate change. Sea ice also affects shipping routes through the polar regions.
(0 - 1)  
rsn 33 Snow density This parameter is the mass of snow per cubic metre in the snow layer.

The ECMWF Integrated Forecast System (IFS) model represents snow as a single additional layer over the uppermost soil level. The snow may cover all or part of the grid box.

See further information on snow in the IFS.
kg m**-3  
swvl1 39 Volumetric soil water layer 1 This parameter is the volume of water in soil layer 1 (0 - 7cm, the surface is at 0cm).

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:
Layer 1: 0 - 7cm
Layer 2: 7 - 28cm
Layer 3: 28 - 100cm
Layer 4: 100 - 289cm

The volumetric soil water is associated with the soil texture (or classification), soil depth, and the underlying groundwater level.
m**3 m**-3  
swvl2 40 Volumetric soil water layer 2 This parameter is the volume of water in soil layer 2 (7 - 28cm, the surface is at 0cm).

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:
Layer 1: 0 - 7cm
Layer 2: 7 - 28cm
Layer 3: 28 - 100cm
Layer 4: 100 - 289cm

The volumetric soil water is associated with the soil texture (or classification), soil depth, and the underlying groundwater level.
m**3 m**-3  
swvl3 41 Volumetric soil water layer 3 This parameter is the volume of water in soil layer 3 (28 - 100cm, the surface is at 0cm).

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:
Layer 1: 0 - 7cm
Layer 2: 7 - 28cm
Layer 3: 28 - 100cm
Layer 4: 100 - 289cm

The volumetric soil water is associated with the soil texture (or classification), soil depth, and the underlying groundwater level.
m**3 m**-3  
swvl4 42 Volumetric soil water layer 4 This parameter is the volume of water in soil layer 4 (100 - 289cm, the surface is at 0cm).

The ECMWF Integrated Forecasting System model has a four-layer representation of soil:
Layer 1: 0 - 7cm
Layer 2: 7 - 28cm
Layer 3: 28 - 100cm
Layer 4: 100 - 289cm

The volumetric soil water is associated with the soil texture (or classification), soil depth, and the underlying groundwater level.
m**3 m**-3  
mx2t24 51 Maximum temperature at 2 metres in the last 24 hours The highest value of 2 metre temperature in the previous 24 hour period.

2m temperature is calculated by interpolating between the lowest model level and the Earth's surface, taking account of the atmospheric conditions. See further information.

This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.
K  
mn2t24 52 Minimum temperature at 2 metres in the last 24 hours The lowest value of 2 metre temperature in the previous 24 hour period.

2m temperature is calculated by interpolating between the lowest model level and the Earth's surface, taking account of the atmospheric conditions. See further information.

This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.
K  
mean2t24 55 Mean temperature at 2 metres in the last 24 hours The mean value of 2 metre temperature in the previous 24 hour period. The mean is calculated from the temperature at each model time step.

2m temperature is calculated by interpolating between the lowest model level and the Earth's surface, taking account of the atmospheric conditions. See further information.

This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15
K  
tclw 78 Total column cloud liquid water This parameter is the amount of liquid water contained within cloud droplets in a column extending from the surface of the Earth to the top of the atmosphere. Rain water droplets, which are much larger in size (and mass), are not included in this parameter.

This parameter represents the area averaged value for a model grid box.

Clouds contain a continuum of different- sized water droplets and ice particles. The ECMWF Integrated Forecasting System (IFS) cloud scheme simplifies this to represent a number of discrete cloud droplets/particles including: cloud water droplets, raindrops, ice crystals and snow (aggregated ice crystals). The processes of droplet formation, phase transition and aggregation are also highly simplified in the IFS.
kg m**-2  
tciw 79 Total column cloud ice water This parameter is the amount of ice contained within clouds in a column extending from the surface of the Earth to the top of the atmosphere. Snow (aggregated ice crystals) is not included in this parameter.

This parameter represents the area averaged value for a model grid box.

Clouds contain a continuum of different- sized water droplets and ice particles. The ECMWF Integrated Forecasting System (IFS) cloud scheme simplifies this to represent a number of discrete cloud droplets/particles including: cloud water droplets, raindrops, ice crystals and snow (aggregated ice crystals). The processes of droplet formation, phase transition and aggregation are also highly simplified in the IFS.
kg m**-2  
z 129 Geopotential This parameter is the gravitational potential energy of a unit mass, at a particular location, relative to mean sea level. It is also the amount of work that would have to be done, against the force of gravity, to lift a unit mass to that location from mean sea level.

The geopotential height can be calculated by dividing the geopotential by the Earth's gravitational acceleration, g (=9.80665 m s-2). The geopotential height plays an important role in synoptic meteorology (analysis of weather patterns). Charts of geopotential height plotted at constant pressure levels (e.g., 300, 500 or 850 hPa) can be used to identify weather systems such as cyclones, anticyclones, troughs and ridges.

At the surface of the Earth, this parameter shows the variations in geopotential (height) of the surface, and is often referred to as the orography.
m**2 s**-2  
tcwv 137 Total column water vapour This parameter is the total amount of water vapour in a column extending from the surface of the Earth to the top of the atmosphere.

This parameter represents the area averaged value for a grid box.
kg m**-2  
sd 141 Snow depth This parameter is the depth of snow from the snow-covered area of a grid box.

Its units are metres of water equivalent, so it is the depth the water would have if the snow melted and was spread evenly over the whole grid box. The ECMWF Integrated Forecast System represents snow as a single additional layer over the uppermost soil level. The snow may cover all or part of the grid box.

See further information.
m of water equivalent  
lsp 142 Large-scale precipitation This parameter is the accumulated liquid and frozen water, comprising rain and snow, that falls to the Earth's surface and which is generated by the cloud scheme in the ECMWF Integrated Forecasting System (IFS). The cloud scheme represents the formation and dissipation of clouds and large-scale precipitation due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly by the IFS at spatial scales of the grid box or larger. Precipitation can also be generated by the convection scheme in the IFS, which represents convection at spatial scales smaller than the grid box. See further information. This parameter does not include fog, dew or the precipitation that evaporates in the atmosphere before it lands at the surface of the Earth.

This parameter is the total amount of water accumulated over a particular time period which depends on the data extracted. The units of this parameter are depth in metres of water equivalent. It is the depth the water would have if it were spread evenly over the grid box.

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box.
m  
cp 143 Convective precipitation This parameter is the accumulated liquid and frozen water, comprising rain and snow, that falls to the Earth's surface and which is generated by the convection scheme in the ECMWF Integrated Forecasting System (IFS). The convection scheme represents convection at spatial scales smaller than the grid box. Precipitation can also be generated by the cloud scheme in the IFS, which represents the formation and dissipation of clouds and large-scale precipitation due to changes in atmospheric quantities (such as pressure, temperature and moisture) predicted directly at spatial scales of the grid box or larger. See further information. This parameter does not include fog, dew or the precipitation that evaporates in the atmosphere before it lands at the surface of the Earth.

This parameter is the total amount of water accumulated over a particular time period which depends on the data extracted. The units of this parameter are depth in metres of water equivalent. It is the depth the water would have if it were spread evenly over the grid box.

Care should be taken when comparing model parameters with observations, because observations are often local to a particular point in space and time, rather than representing averages over a model grid box.
m  
sshf 146 Surface sensible heat flux This parameter is the transfer of heat between the Earth's surface and the atmosphere through the effects of turbulent air motion (but excluding any heat transfer resulting from condensation or evaporation).

The magnitude of the sensible heat flux is governed by the difference in temperature between the surface and the overlying atmosphere, wind speed and the surface roughness. For example, cold air overlying a warm surface would produce a sensible heat flux from the land (or ocean) into the atmosphere. See further documentation

This is a single level parameter and it is accumulated over a particular time period which depends on the data extracted.The units are joules per square metre (J m-2). To convert to watts per square metre (W m-2), the accumulated values should be divided by the accumulation period expressed in seconds. The ECMWF convention for vertical fluxes is positive downwards.
J m**-2  
slhf 147 Surface latent heat flux This parameter is the transfer of latent heat (resulting from water phase changes, such as evaporation or condensation) between the Earth's surface and the atmosphere through the effects of turbulent air motion. Evaporation from the Earth's surface represents a transfer of energy from the surface to the atmosphere. See further documentation

This parameter is accumulated over a particular time period which depends on the data extracted.The units are joules per square metre (J m-2). To convert to watts per square metre (W m-2), the accumulated values should be divided by the accumulation period expressed in seconds.

The ECMWF convention for vertical fluxes is positive downwards.
J m**-2  
gh 156 Geopotential Height This parameter is a measure of the height of a point in the atmosphere in relation to its potential energy. It is calculated by dividing the geopotential by the Earth's mean gravitational acceleration, g (=9.80665 m s-2). The geopotential is the gravitational potential energy of a unit mass, at a particular location, relative to mean sea level. Geopotential is also the amount of work that would have to be done, against the force of gravity, to lift a unit mass to that location from mean sea level.

This parameter plays an important role in synoptic meteorology (analysis of weather patterns). Charts of geopotential height plotted at constant pressure levels (e.g., 300, 500 or 850 hPa) can be used to identify weather systems such as cyclones, anticyclones, troughs and ridges. At the surface of the Earth, this parameter shows the variations in geopotential height of the surface, and is often referred to as the orography.

The units of this parameter are geopotential metres. A geopotential metre is approximately 2% shorter than a geometric metre.
gpm  
stl2 170 Soil temperature level 2 This parameter is the temperature of the soil at level 2 (in the middle of layer 2).

The ECMWF Integrated Forecasting System (IFS) has a four-layer representation of soil, where the surface is at 0cm:

Layer 1: 0 - 7cm
Layer 2: 7 - 28cm
Layer 3: 28 - 100cm
Layer 4: 100 - 289cm

Soil temperature is set at the middle of each layer, and heat transfer is calculated at the interfaces between them. It is assumed that there is no heat transfer out of the bottom of the lowest layer.

This parameter has units of Kelvin (K). Temperature measured in Kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

See further information.
K  
lsm 172 Land-sea mask This parameter is the proportion of land, as opposed to ocean or inland waters (lakes, reservoirs, rivers and coastal waters), in a grid box.
This parameter has values ranging between zero and one and is dimensionless.
In cycles of the ECMWF Integrated Forecasting System (IFS) from CY41R1 (introduced in May 2015) onwards, grid boxes where this parameter has a value above 0.5 can be comprised of a mixture of land and inland water but not ocean. Grid boxes with a value of 0.5 and below can only be comprised of a water surface. In the latter case, the lake cover is used to determine how much of the water surface is ocean or inland water.
In cycles of the IFS before CY41R1, grid boxes where this parameter has a value above 0.5 can only be comprised of land and those grid boxes with a value of 0.5 and below can only be comprised of ocean. In these older model cycles, there is no differentiation between ocean and inland water.
(0 - 1)  
ssr 176 Surface net solar radiation This parameter is the amount of solar radiation (also known as shortwave radiation) that reaches a horizontal plane at the surface of the Earth (both direct and diffuse) minus the amount reflected by the Earth's surface (which is governed by the albedo).

Radiation from the Sun (solar, or shortwave, radiation) is partly reflected back to space by clouds and particles in the atmosphere (aerosols) and some of it is absorbed. The remainder is incident on the Earth's surface, where some of it is reflected. See further documentation.

This parameter is accumulated over a particular time period which depends on the data extracted. The units are joules per square metre (J m-2). To convert to watts per square metre (W m-2), the accumulated values should be divided by the accumulation period expressed in seconds. The ECMWF convention for vertical fluxes is positive downwards.
J m**-2  
str 177 Surface net thermal radiation Thermal radiation (also known as longwave or terrestrial radiation) refers to radiation emitted by the atmosphere, clouds and the surface of the Earth. This parameter is the difference between downward and upward thermal radiation at the surface of the Earth. It the amount passing through a horizontal plane.

The atmosphere and clouds emit thermal radiation in all directions, some of which reaches the surface as downward thermal radiation. The upward thermal radiation at the surface consists of thermal radiation emitted by the surface plus the fraction of downwards thermal radiation reflected upward by the surface. See further documentation.

This parameter is accumulated over a particular time period which depends on the data extracted. The units are joules per square metre (J m-2). To convert to watts per square metre (W m-2), the accumulated values should be divided by the accumulation period expressed in seconds.

The ECMWF convention for vertical fluxes is positive downwards.
J m**-2  
tsr 178 Top net solar radiation This parameter is the incoming solar radiation (also known as shortwave radiation) minus the outgoing solar radiation at the top of the atmosphere. It is the amount of radiation passing through a horizontal plane. The incoming solar radiation is the amount received from the Sun. The outgoing solar radiation is the amount reflected and scattered by the Earth's atmosphere and surface. See further documentation.

This parameter is accumulated over a particular time period which depends on the data extracted. The units are joules per square metre (J m-2). To convert to watts per square metre (W m-2), the accumulated values should be divided by the accumulation period expressed in seconds.

The ECMWF convention for vertical fluxes is positive downwards.
J m**-2  
ttr 179 Top net thermal radiation The thermal (also known as terrestrial or longwave) radiation emitted to space at the top of the atmosphere is commonly known as the Outgoing Longwave Radiation (OLR). The top net thermal radiation (this parameter) is equal to the negative of OLR. See further documentation.

This parameter is accumulated over a particular time period which depends on the data extracted. The units are joules per square metre (J m-2). To convert to watts per square metre (W m-2), the accumulated values should be divided by the accumulation period expressed in seconds.The ECMWF convention for vertical fluxes is positive downwards.
J m**-2  
ewss 180 Eastward turbulent surface stress Air flowing over a surface exerts a stress that transfers momentum to the surface and slows the wind. This parameter is the accumulated stress on the Earth's surface in the eastward direction due to both the turbulent interactions between the atmosphere and the surface, and to turbulent orographic form drag. The turbulent interactions between the atmosphere and the surface are due to the roughness of the surface. The turbulent orographic form drag is the stress due to the valleys, hills and mountains on horizontal scales below 5km being derived from land surface data at about 1 km resolution. See further information.

Positive (negative) values denote stress in the eastward (westward) direction.

This parameter is accumulated over a particular time period which depends on the data extracted.
N m**-2 s  
nsss 181 Northward turbulent surface stress Air flowing over a surface exerts a stress that transfers momentum to the surface and slows the wind. This parameter is the accumulated stress on the Earth's surface in the northward direction due to both the turbulent interactions between the atmosphere and the surface, and to turbulent orographic form drag.

The turbulent interactions between the atmosphere and the surface are due to the roughness of the surface.

The turbulent orographic form drag is the stress due to the valleys, hills and mountains on horizontal scales below 5km being derived from land surface data at about 1 km resolution. See further information.

Positive (negative) values denote stress in the northward (southward) direction.

This parameter is accumulated over a particular time period which depends on the data extracted.
N m**-2 s  
e 182 Evaporation This parameter is the accumulated amount of water that has evaporated from the Earth's surface, including a simplified representation of transpiration (from vegetation), into vapour in the air above.

This parameter is accumulated over a particular time period which depends on the data extracted.

The ECMWF Integrated Forecasting System convention is that downward fluxes are positive. Therefore, negative values indicate evaporation and positive values indicate condensation.
m of water equivalent  
stl3 183 Soil temperature level 3 This parameter is the temperature of the soil at level 3 (in the middle of layer 3).

The ECMWF Integrated Forecasting System (IFS) has a four-layer representation of soil, where the surface is at 0cm:

Layer 1: 0 - 7cm
Layer 2: 7 - 28cm
Layer 3: 28 - 100cm
Layer 4: 100 - 289cm

Soil temperature is set at the middle of each layer, and heat transfer is calculated at the interfaces between them. It is assumed that there is no heat transfer out of the bottom of the lowest layer.

This parameter has units of Kelvin (K). Temperature measured in Kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

See further information.
K  
lcc 186 Low cloud cover This parameter is the proportion of a grid box covered by cloud occurring in the lower levels of the troposphere. Low cloud is a single level field calculated from cloud occurring on model levels with a pressure greater than 0.8 times the surface pressure. So, if the surface pressure is 1000 hPa (hectopascal), low cloud would be calculated using levels with a pressure greater than 800 hPa (below approximately 2km (assuming a 'standard atmosphere')).

The low cloud cover parameter is calculated from cloud cover for the appropriate model levels as described above. Assumptions are made about the degree of overlap/randomness between clouds in different model levels.

Cloud fractions vary from 0 to 1.
(0 - 1)  
sund 189 Sunshine duration This parameter is the length of time in which the direct solar (shortwave) radiation at the Earth's surface, falling on a plane perpendicular to the direction of the Sun, is greater than or equal to 120 W m-2.

The minimum solar intensity level of 120 W m-2 is defined by the World Meteorological Organisation and is consistent with observed values of sunshine duration from a Campbell-Stokes recorder (sometimes called a Stokes sphere) that can only measure moderately intense sunlight and brighter.

This parameter is accumulated over a particular time period which depends on the data extracted.
s  
ro 205 Runoff Some water from rainfall, melting snow, or deep in the soil, stays stored in the soil. Otherwise, the water drains away, either over the surface (surface runoff), or under the ground (sub-surface runoff) and the sum of these two is simply called 'runoff'. This parameter is the total amount of water accumulated over a particular time period which depends on the data extracted.The units of runoff are depth in metres. This is the depth the water would have if it were spread evenly over the grid box. Care should be taken when comparing model parameters with observations, because observations are often local to a particular point rather than averaged over a grid square area. Observations are also often taken in different units, such as mm/day, rather than the accumulated metres produced here.

Runoff is a measure of the availability of water in the soil, and can, for example, be used as an indicator of drought or flood. More information about how runoff is calculated is given in the IFS Physical Processes documentation.
m  
tco3 206 Total column ozone This parameter is the total amount of ozone in a column of air extending from the surface of the Earth to the top of the atmosphere. This parameter can also be referred to as total ozone, or vertically integrated ozone. The values are dominated by ozone within the stratosphere.

In the ECMWF Integrated Forecasting System (IFS), there is a simplified representation of ozone chemistry (including representation of the chemistry which has caused the ozone hole). Ozone is also transported around in the atmosphere through the motion of air. See further documentation .

Naturally occurring ozone in the stratosphere helps protect organisms at the surface of the Earth from the harmful effects of ultraviolet (UV) radiation from the Sun. Ozone near the surface, often produced because of pollution, is harmful to organisms.

In the IFS, the units for total ozone are kilograms per square metre, but before 12/06/2001 dobson units were used. Dobson units (DU) are still used extensively for total column ozone. 1 DU = 2.1415E-5 kg m-2
kg m**-2  
tisr 212 TOA incident solar radiation Accumulated field J m**-2  
stl4 236 Soil temperature level 4 This parameter is the temperature of the soil at level 4 (in the middle of layer 4).

The ECMWF Integrated Forecasting System (IFS) has a four-layer representation of soil, where the surface is at 0cm:

Layer 1: 0 - 7cm
Layer 2: 7 - 28cm
Layer 3: 28 - 100cm
Layer 4: 100 - 289cm

Soil temperature is set at the middle of each layer, and heat transfer is calculated at the interfaces between them. It is assumed that there is no heat transfer out of the bottom of the lowest layer.

This parameter has units of Kelvin (K). Temperature measured in Kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

See further information.
K  
fal 243 Forecast albedo This parameter is a measure of the reflectivity of the Earth's surface. It is the fraction of solar (shortwave) radiation reflected by Earth's surface, across the solar spectrum, for both direct and diffuse radiation. Typically, snow and ice have high reflectivity with albedo values of 0.8 and above, land has intermediate values between about 0.1 and 0.4 and the ocean has low values of 0.1 or less.

Radiation from the Sun (solar, or shortwave, radiation) is partly reflected back to space by clouds and particles in the atmosphere (aerosols) and some of it is absorbed. The rest is incident on the Earth's surface, where some of it is reflected. The portion that is reflected by the Earth's surface depends on the albedo. See further documentation .

In the ECMWF Integrated Forecasting System (IFS), a climatological background albedo (observed values averaged over a period of several years) is used, modified by the model over water, ice and snow.

Albedo is often shown as a percentage (%).
(0 - 1)  
dl 228007 Lake total depth This parameter is the mean depth of inland water bodies (lakes, reservoirs and rivers) and coastal waters. This field is specified from in-situ measurements and indirect estimates and is constant in time.

ECMWF implemented a lake model in May 2015 to represent the water temperature and lake ice of all the world's major inland water bodies in the Integrated Forecasting System (IFS). The IFS differentiates between (i) ocean water, handled by the ocean model, and (ii) inland water (lakes, reservoirs and rivers) and coastal waters handled by the lake parametrisation. Lake depth and surface area (or fractional cover) are kept constant in time.
m  
lmlt 228008 Lake mix-layer temperature This parameter is the temperature of the uppermost layer of inland water bodies (lakes, reservoirs and rivers) or coastal waters, that is well mixed and has a near constant temperature with depth (i.e., a uniform distribution of temperature with depth).

The ECMWF Integrated Forecasting System represents inland water bodies and coastal waters with two layers in the vertical, the mixed layer above and the thermocline below. The upper boundary of the thermocline is located at the mixed layer bottom, and the lower boundary of the thermocline at the lake bottom.

Mixing within the mixed layer can occur when the density of the surface (and near-surface) water is greater than that of the water below. Mixing can also occur through the action of wind on the surface of the lake.

This parameter has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

ECMWF implemented a lake model in May 2015 to represent the water temperature and lake ice of all the world's major inland water bodies in the Integrated Forecasting System (IFS). The IFS differentiates between (i) ocean water, handled by the ocean model, and (ii) inland water (lakes, reservoirs and rivers) and coastal waters handled by the lake parametrisation. Lake depth and surface area (or fractional cover) are kept constant in time.
K  
licd 228014 Lake ice total depth This parameter is the thickness of ice on inland water bodies (lakes, reservoirs and rivers) and coastal waters.

The ECMWF Integrated Forecasting System represents the formation and melting of ice on inland water bodies. A single ice layer is represented. This parameter is the thickness of that ice layer.

ECMWF implemented a lake model in May 2015 to represent the water temperature and lake ice of all the world's major inland water bodies in the Integrated Forecasting System (IFS). The IFS differentiates between (i) ocean water, handled by the ocean model, and (ii) inland water (lakes, reservoirs and rivers) and coastal waters handled by the lake parametrisation. Lake depth and surface area (or fractional cover) are kept constant in time.
m  

V-v-c: Pressure levels 12-houlry

Available at 1000, 925, 850, 700, 500, 400, 300, 200 hPa unless otherwise specified.

Ranges Forecast time step Base times Resolution
T+0h to T+5160h 12-hourly 00 UTC
  • 0.4° x 0.4° lat/long grid or any multiple thereof (global or sub-area)
  • 0.75° x 0.75° lat/long grid or any multiple thereof (global or sub-area)
  • On model (Gaussian) O320 (35 km) grid (global or sub-area)
  • Spectral components (T319) for upper-air fields (global area only)
Short Name ID Long Name Description Units Additional information
z 129 Geopotential This parameter is the gravitational potential energy of a unit mass, at a particular location, relative to mean sea level. It is also the amount of work that would have to be done, against the force of gravity, to lift a unit mass to that location from mean sea level.

The geopotential height can be calculated by dividing the geopotential by the Earth's gravitational acceleration, g (=9.80665 m s-2). The geopotential height plays an important role in synoptic meteorology (analysis of weather patterns). Charts of geopotential height plotted at constant pressure levels (e.g., 300, 500 or 850 hPa) can be used to identify weather systems such as cyclones, anticyclones, troughs and ridges.

At the surface of the Earth, this parameter shows the variations in geopotential (height) of the surface, and is often referred to as the orography.
m**2 s**-2  
t 130 Temperature This parameter is the temperature in the atmosphere.

It has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

This parameter is available on multiple levels through the atmosphere.
K  
u 131 U component of wind This parameter is the eastward component of the wind. It is the horizontal speed of air moving towards the east, in metres per second. A negative sign thus indicates air movement towards the west.

This parameter can be combined with the V component of wind to give the speed and direction of the horizontal wind.
m s**-1  
v 132 V component of wind This parameter is the northward component of the wind. It is the horizontal speed of air moving towards the north, in metres per second. A negative sign thus indicates air movement towards the south.

This parameter can be combined with the U component of wind to give the speed and direction of the horizontal wind.
m s**-1  
q 133 Specific humidity This parameter is the mass of water vapour per kilogram of moist air.

The total mass of moist air is the sum of the dry air, water vapour, cloud liquid, cloud ice, rain and falling snow.
kg kg**-1  
vo 138 Vorticity (relative) This parameter is a measure of the rotation of air in the horizontal, around a vertical axis, relative to a fixed point on the surface of the Earth.

On the scale of weather systems, troughs (weather features that can include rain) are associated with anticlockwise rotation (in the northern hemisphere), and ridges (weather features that bring light or still winds) are associated with clockwise rotation.

Adding the rotation of the Earth, the so-called Coriolis parameter, to the relative vorticity produces the absolute vorticity.
s**-1  
d 155 Divergence This parameter is the horizontal divergence of velocity. It is the rate at which air is spreading out horizontally from a point, per square metre. This parameter is positive for air that is spreading out, or diverging, and negative for the opposite, for air that is concentrating, or converging (convergence). s**-1  
gh 156 Geopotential Height This parameter is a measure of the height of a point in the atmosphere in relation to its potential energy. It is calculated by dividing the geopotential by the Earth's mean gravitational acceleration, g (=9.80665 m s-2). The geopotential is the gravitational potential energy of a unit mass, at a particular location, relative to mean sea level. Geopotential is also the amount of work that would have to be done, against the force of gravity, to lift a unit mass to that location from mean sea level.

This parameter plays an important role in synoptic meteorology (analysis of weather patterns). Charts of geopotential height plotted at constant pressure levels (e.g., 300, 500 or 850 hPa) can be used to identify weather systems such as cyclones, anticyclones, troughs and ridges. At the surface of the Earth, this parameter shows the variations in geopotential height of the surface, and is often referred to as the orography.

The units of this parameter are geopotential metres. A geopotential metre is approximately 2% shorter than a geometric metre.
gpm  
o3 203 Ozone mass mixing ratio This parameter is the mass of ozone per kilogram of air.

In the ECMWF Integrated Forecasting System (IFS), there is a simplified representation of ozone chemistry (including representation of the chemistry which has caused the ozone hole). Ozone is also transported around in the atmosphere through the motion of air. See further documentation.

Naturally occurring ozone in the stratosphere helps protect organisms at the surface of the Earth from the harmful effects of ultraviolet (UV) radiation from the Sun. Ozone near the surface, often produced because of pollution, is harmful to organisms.

Most of the IFS chemical species are archived as mass mixing ratios [kg kg-1]. This link explains how to convert to concentration in terms of mass per unit volume.
kg kg**-1  

V-v-d: Individual forecast runs - 12-hourly - Model levels

Short Name ID Long Name Description Units Additional information
z 129 Geopotential This parameter is the gravitational potential energy of a unit mass, at a particular location, relative to mean sea level. It is also the amount of work that would have to be done, against the force of gravity, to lift a unit mass to that location from mean sea level.

The geopotential height can be calculated by dividing the geopotential by the Earth's gravitational acceleration, g (=9.80665 m s-2). The geopotential height plays an important role in synoptic meteorology (analysis of weather patterns). Charts of geopotential height plotted at constant pressure levels (e.g., 300, 500 or 850 hPa) can be used to identify weather systems such as cyclones, anticyclones, troughs and ridges.

At the surface of the Earth, this parameter shows the variations in geopotential (height) of the surface, and is often referred to as the orography.
m**2 s**-2  
t 130 Temperature This parameter is the temperature in the atmosphere.

It has units of kelvin (K). Temperature measured in kelvin can be converted to degrees Celsius (°C) by subtracting 273.15.

This parameter is available on multiple levels through the atmosphere.
K  
u 131 U component of wind This parameter is the eastward component of the wind. It is the horizontal speed of air moving towards the east, in metres per second. A negative sign thus indicates air movement towards the west.

This parameter can be combined with the V component of wind to give the speed and direction of the horizontal wind.
m s**-1  
v 132 V component of wind This parameter is the northward component of the wind. It is the horizontal speed of air moving towards the north, in metres per second. A negative sign thus indicates air movement towards the south.

This parameter can be combined with the U component of wind to give the speed and direction of the horizontal wind.
m s**-1  
q 133 Specific humidity This parameter is the mass of water vapour per kilogram of moist air.

The total mass of moist air is the sum of the dry air, water vapour, cloud liquid, cloud ice, rain and falling snow.
kg kg**-1  
vo 138 Vorticity (relative) This parameter is a measure of the rotation of air in the horizontal, around a vertical axis, relative to a fixed point on the surface of the Earth.

On the scale of weather systems, troughs (weather features that can include rain) are associated with anticlockwise rotation (in the northern hemisphere), and ridges (weather features that bring light or still winds) are associated with clockwise rotation.

Adding the rotation of the Earth, the so-called Coriolis parameter, to the relative vorticity produces the absolute vorticity.
s**-1  
lnsp 152 Logarithm of surface pressure This parameter is the natural logarithm of pressure (force per unit area) of the atmosphere on the surface of land, sea and inland water. Numerical weather prediction models often utilise the logarithm of surface pressure in their calculations. ~  
d 155 Divergence This parameter is the horizontal divergence of velocity. It is the rate at which air is spreading out horizontally from a point, per square metre. This parameter is positive for air that is spreading out, or diverging, and negative for the opposite, for air that is concentrating, or converging (convergence). s**-1  
clwc 246 Specific cloud liquid water content This parameter is the mass of cloud liquid water droplets per kilogram of the total mass of moist air. The 'total mass of moist air' is the sum of the dry air, water vapour, cloud liquid, cloud ice, rain and falling snow. This parameter represents the average value for a grid box.

Water within clouds can be liquid or ice, or a combination of the two. See further information about the cloud formulation.
kg kg**-1  
ciwc 247 Specific cloud ice water content This parameter is the mass of cloud ice particles per kilogram of the total mass of moist air. The 'total mass of moist air' is the sum of the dry air, water vapour, cloud liquid, cloud ice, rain and falling snow. This parameter represents the average value for a grid box.

Water within clouds can be liquid or ice, or a combination of the two.
Note that 'cloud frozen water' is the same as 'cloud ice water'.

See further information about the cloud formulation.
kg kg**-1  

V-v-e Wave seasonal forecast - 24-hourly

Short Name ID Long Name Description Units Additional information
mp1 140220 Mean wave period based on first moment This parameter is the reciprocal of the mean frequency of the wave components that represent the sea state. All wave components have been averaged proportionally to their respective amplitude. This parameter can be used to estimate the magnitude of Stokes drift transport in deep water.

The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). Moments are statistical quantities derived from the two-dimensional wave spectrum.
s  
mp2 140221 Mean zero-crossing wave period This parameter represents the mean length of time between occasions where the sea/ocean surface crosses mean sea level. In combination with wave height information, it could be used to assess the length of time that a coastal structure might be under water, for example.

The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). In the ECMWF Integrated Forecasting System this parameter is calculated from the characteristics of the two-dimensional wave spectrum.
s  
swh 140229 Significant height of combined wind waves and swell This parameter represents the average height of the highest third of surface ocean/sea waves generated by wind and swell. It represents the vertical distance between the wave crest and the wave trough.

The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum).

The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. This parameter takes account of both.

More strictly, this parameter is four times the square root of the integral over all directions and all frequencies of the two-dimensional wave spectrum. See further documentation.

This parameter can be used to assess sea state and swell. For example, engineers use significant wave height to calculate the load on structures in the open ocean, such as oil platforms, or in coastal applications.
m  
mwd 140230 Mean wave direction This parameter is the mean direction of ocean/sea surface waves. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). This parameter is a mean over all frequencies and directions of the two-dimensional wave spectrum.

The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. This parameter takes account of both. See further documentation.

This parameter can be used to assess sea state and swell. For example, engineers use this type of wave information when designing structures in the open ocean, such as oil platforms, or in coastal applications.

The units are degree true which means the direction relative to the geographic location of the north pole. Zero means 'coming from the north' and 90 'coming from the east'.
Degree true  
pp1d 140231 Peak wave period This parameter represents the period of the most energetic ocean waves generated by local winds and associated with swell. The wave period is the average time it takes for two consecutive wave crests, on the surface of the ocean/sea, to pass through a fixed point.

The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). This parameter is calculated from the reciprocal of the frequency corresponding to the largest value (peak) of the frequency wave spectrum. The frequency wave spectrum is obtained by integrating the two-dimensional wave spectrum over all directions.

The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. This parameter takes account of both.
s  
mwp 140232 Mean wave period This parameter is the average time it takes for two consecutive wave crests, on the surface of the ocean/sea, to pass through a fixed point. The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). This parameter is a mean over all frequencies and directions of the two-dimensional wave spectrum.

The wave spectrum can be decomposed into wind-sea waves, which are directly affected by local winds, and swell, the waves that were generated by the wind at a different location and time. This parameter takes account of both. See further documentation.

This parameter can be used to assess sea state and swell. For example, engineers use such wave information when designing structures in the open ocean, such as oil platforms, or in coastal applications.
s  
cdww 140233 Coefficient of drag with waves This parameter is the resistance that ocean waves exert on the atmosphere. It is sometimes also called a 'friction coefficient'.

It is calculated by the wave model as the ratio of the square of the friction velocity, to the square of the neutral wind speed at a height of 10 metres above the surface of the Earth.

The neutral wind is calculated from the surface stress and the corresponding roughness length by assuming that the air is neutrally stratified. The neutral wind is, by definition, in the direction of the surface stress. The size of the roughness length depends on the sea state.
dimensionless  
msqs 140244 Mean square slope of waves This parameter can be related analytically to the average slope of combined wind-sea and swell waves. It can also be expressed as a function of wind speed under some statistical assumptions. The higher the slope, the steeper the waves. This parameter indicates the roughness of the sea/ocean surface which affects the interaction between ocean and atmosphere. See further information.

The ocean/sea surface wave field consists of a combination of waves with different heights, lengths and directions (known as the two-dimensional wave spectrum). This parameter is derived statistically from the two-dimensional wave spectrum.
dimensionless  
wind 140245 10 metre wind speed This parameter is the horizontal speed of the 'neutral wind', at a height of ten metres above the surface of the Earth. The units of this parameter are metres per second.

The neutral wind is calculated from the surface stress and the corresponding roughness length by assuming that the air is neutrally stratified. The neutral wind is, by definition, in the direction of the surface stress. The size of the roughness length depends on sea state.

This parameter is the wind speed used to force the wave model, therefore it is only calculated over water bodies represented in the ocean wave model. It is interpolated from the atmospheric model's horizontal grid onto the horizontal grid used by the ocean wave model.
m s**-1  
dwi 140249 10 metre wind direction This parameter is the direction from which the 'neutral wind' blows, in degrees clockwise from true north, at a height of ten metres above the surface of the Earth.

The neutral wind is calculated from the surface stress and roughness length by assuming that the air is neutrally stratified. The neutral wind is, by definition, in the direction of the surface stress. The size of the roughness length depends on the sea state.

This parameter is the wind direction used to force the wave model, therefore it is only calculated over water bodies represented in the ocean wave model. It is interpolated from the atmospheric model's horizontal grid onto the horizontal grid used by the ocean wave model.
degrees  

Last updated: 23-09-2020