Revisions during 1999

9 March 1999 Introduction of 50 level model (Cy19r2)

This version has 50 levels in the vertical instead of 31 in the operational version, most of the extra resolution being in the stratosphere between 150 hPa and 0.1 hPa (the current operational model top level is at 10 hPa). Horizontal spectral and physical truncations are kept unchanged (T_L319). The model resolution in the Ensemble Prediction System (EPS) will continue to be T_L159L31.

An article from the ECMWF Newsletter describing these changes is given in pdf (784 KB)file.

5 May 1999 Introduction of Cy21r1 of the model changes include:

1. processing and assimilation of raw TOVS/ATOVS radiance data from the NOAA-14/NOAA-15 polar orbiting spacecraft (note that current operational assimilation is reduced t one - NOAA-14 - spacecraft since NOAA-11 failure on 27.2.1999); the move to assimilating raw radiance data (as opposed to the NESDIS pre-processed radiances that were previously used) has required a significant review of the errors assigned to radiance observations in the analysis and new quality control procedures;

2. a complete rewriting of the sea (and lakes) surface temperature and ice concentration software resulting in the correction of several minor inconsistencies.

13 July 1999 Cy21r2 of the model, the list of important changes introduced on this occasion includes:

1. a new coupling of the physics with the dynamics;

2. a new optimal interpolation analysis of soil moisture and temperature, using the analysis of screen-level temperature and humidity introduced in March;

An article from the ECMWF Newsletter describing these changes is given in pdf (616 KB) file.

3. US profilers and dropsonde data are used; radiosonde temperatures are bias corrected using information carried out in the TEMP message; ship winds are assigned to a height consistent with the information reported in WMO tables; ship humidity data are blacklisted;

4. waves slope and wind stress formulations are improved in the oceanic wave package

12 October 1999 Introduction of cy21r4 with 60 levels in the vertical for the reference model (T319) and 40 levels in the EPS (T159). Other changes include:

• new global orographics and associated subgrid orography fields;



• extensive changes in the cloud and convection schemes;



• a new post-processing of 10m winds aimed at a better representation of weather station environments;



• a revised evaluation of the model error cost function used in 4D-Var (Jb);



• a revised scheme for the correction of satellite radiance biases;



• active assimilation of SSM/I wind speed;



• bugfix of the humidity computation from SYNOP and TEMP observation below zero degree Celsius;



• introduction of ozone variable.

An article from the ECMWF Newsletter describing these changes is given in pdf (204 KB) file.

ECMWF has issued the following warning about this data.

During the operation of cy21r4 of the ECMWF model from 12 October 1999 to 10 April 2000 the humidity fields in the lower stratosphere both in the analysis and forecast were seriously affected by erroneous moisture. These fields should not be used for research and it is recommended that the model results from the operational archive are not used to provide initial conditions for numerical experiments during this period.

The error is up to 1 to 2 orders of magnitude in a shallow layer just above the tropopause.

This may have a slight affect on the temperature in some regions.