Revisions during 1989

31 January 1989 A set of changes to the use of satellite data was introduced. They include:

1. a stability check of the temperature profiles deduced from the TOVS. As large errors in the lowest layer of TOVS data tend to be compensated aloft by errors of opposite sign, incorrect data are spotted by checking the difference in temperature between two layers, namely 1000/700 and 500/300 hPa, against the first-guess. The first guess check is also tightened for certain layers.



2. a revision of the observation error statistics for thicknesses: the horizontal correlation function is flattened and the error variances are distributed more evenly to the different layers.



3. a change to the SATOB OI-check: as introduced for SATEM in July 1988, SATOB are now checked without influence from neighbouring data of the same type.



4. modifications to the use of Precipitable Water Content data (PWC) from NOAA-10 and NOAA-11. The PWC are not used over land, nor when no thickness data are available in the same report; their observation error has been increased.

2 May 1989 Forecast mode cycle 32. A set of three important modifications to the model's physics was implemented in the operational forecasting system:

1. A new parametrisation scheme for radiative fluxes and the representation of cloud optical. properties.



2. A reformulation of cumulus parametrisation using the mass flux approach.



3. A revision of the gravity wave drag formulation.

An article from the ECMWF Newsletter describing these changes is given in pdf (184 KB) file.

4 July 1989 Forecast model cycle 33. Modification to the shallow convection scheme.

16 August 1989 Forecast model cycle 34. The surface analysis code was replaced. It was mainly a technical development, the analysis of surface variables now being performed inside the context of the main analysis program rather than in a separate step. Little meteorological impact should be seen on the sea surface temperature (SST) and snow analysis (the only surface variables currently analysed).

29 August 1989 Various modifications to the analysis were implemented, the most significant of these being :

1. a tighter first-guess check for AIREPs reporting zero wind speed;



2. assigning single level pressure (height) observations to the first-guess pressure level instead of the reported pressure - this will remove spurious analysis increments in the temperature of the lowest model level;
   
   
3. rather than having a uniform global threshold the SATEM stability check will be made dependent on the first-guess error standard deviation.

13 November 1989 Changes to the analysis were implemented:

1. The SST analysis received from NMC Washington and used in the analysis now has a 2° x 2° resolution instead of 5° x 5°. This gives a more detailed description of the SST, particularly in the vicinity of ice and coastal areas. No significant impact is expected on the forecas.



2. The use of SATOB wind data was revised:
   
   
   • the following data are now excluded from the analysis (in addition to the current exclusion of all SATOB over land poleward of 20°): high level GOES wind (P < 500 hPa) north of 20°N, HIMAWARI winds (all levels) poleward of 20°;
     
   
   
   • the asymmetric first-guess cheek was tightened.