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Description of the ECMWF forecasting system in January 2000
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1. ATMOSPHERIC MODEL
ECMWF produces routine global analyses for the four main synoptic hours 00, 06, 12 and 18 UTC and global 10-day forecasts based on 12 UTC data
1.1 Model:
| Numerical scheme | TL319L60 (triangular truncation, resolving up to wavenumber 319 in spectral space, linear reduced Gaussian grid. 60 levels between the earth's surface and 70 km), Semi-Lagrangian two-time-level semi-implicit formulation. |
| Time-step | 20 minutes |
| Smallest wavelength resolved | 125 km |
| Number of grid points in model | 8,300,760 in upper air and 553,384 in surface and sub-surface layers |
| Grid for computation of physical processes is the Gaussian grid, on which single level parameters are available. | The average distance between grid points is close to 62km. |
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Variables at each grid point
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wind, temperature, humidity, cloud fraction and water/ice content (also (recalculated at each time-step) pressure at surface grid-points), ozone |
| Included in model |
orography (terrain height and sub-grid-scale characteristics). Four surface and sub-surface levels (allowing for vegetation cover, gravitational drainage, capillarity exchange, surface and sub-surface runoff), Stratiform and convective precipitation, carbon dioxide (345 ppmv fixed). Aerosol, ozone, solar angle, diffusion, ground & sea roughness, ground and sea-surface temperature, ground humidity, snow-fall, snow-cover and snow melt, radiation (incoming short-wave and out-going long-wave), friction (at surface and in free atmosphere), sub-grid-scale orographic drag, gravity waves and blocking effects, evaporation, sensible and latent heat flux. |
1.2 Data assimilation:
| Global analysis of | wind, temperature, surface pressure and humidity (four-dimensional multivariate variational assimilation on 12-hour periods on all model levels). |
| surface parameters (sea surface temperature from NCEP, sea ice from SSM/I satellite data, soil water content, snow depth, ocean surface waves). | |
| Data used |
about 200,000 pieces of observational data are actually used per 6-hour period after global data checking and selection: In-situ conventional data (SYNOP, TEMP and PILOT over land and sea, DRIBU, aircraft reports). Synthetic data (PAOB) satellite data (TOVS/ATOVS radiances, SCAT surface wind, SSM/I total water vapour, SATOB) |
2. OCEAN WAVE MODELS
2.1 Coupled Ocean Wave Model (WAM Cycle 4)
| Domain | global |
| Numerical scheme |
irregular lat/lon grid, 55 km spacing; spectrum with 25 frequencies and 12 directions including shallow water effects. |
| Coupling | 1 hourly wind forcing of waves, two way interaction of winds and waves, sea state dependent drag coefficient. |
2.2 Limited area model (WAM Cycle 4)
| Domain | North Atlantic, North Sea, Baltic, Mediterranean and Black Sea. |
| Numerical scheme |
irregular lat/lon grid, 28 km spacing; spectrum 25 frequencies and 12 directions. |
| Forcing | 6 hourly wind forcing of waves. |
3. ECMWF ENSEMBLE PREDICTION SYSTEM
ECMWF produces a 51 member ensemble of 10-day forecasts every day, comprising 1 control integration and 50 perturbed integrations.
3.1 Control integration
The control integration is run at TL159L40 resolution using the operational model cycle from the operational TL319 analysis truncated at TL159.
3.2 Perturbed initial conditions
Each member of the 50 perturbed integrations is run from perturbed initial conditions. These perturbations are constucted from fast-growing instabilities of the circulation, calculated from the dominant singular vectors of the forward tangent propagator of the linearised dynamics. Also included in the initial perturbations are more slowly growing structures associated with singular vectors evolved from 2 days earlier.
3.3 Perturbed integrations
The 50 perturbed integrations are run with the same model cycle and resolution as the control integration but with the inclusion of a stochastic physics parametrisation. Each member of the 50 perturbed integrations is run with a set of randomly drawn realisations of the stochastic physics scheme.
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25.01.2006 |
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