Revisions during 1994

2 March 1994 The Integrated Forecast System (IFS) was implemented (cy11r7). The model cycles were renumbered with the introduction of IFS). The IFS is a major rewrite of the forecast model. The model identification field in the GRIB headers of products was changed to 111. Several meteorological modifications were introduced at the same time:

• introduction of the 2 metre dewpoint SYNOP observations in the humidity analysis;



• use of the sensible heat flux in addition to the latent heat flux to determine the cloud base mass flux in the shallow convection scheme;



• inclusion of the latent heat release due to freezing of condensate in convective updraughts.

These modifications addressed certain problems which were noted in the Tropics over the last few months, in particular with precipitation and 2 metre temperature.

4 July 1994 The fields of soil humidity used in the operational system were changed. In order to compensate for a drying out of the model boundary layer which has been noticed over the last few weeks, particularly over Europe and East Asia, the humidity of the soil was reset to field capacity.

This change resulted in a noticeable impact on the temperature in the daytime boundary layer over continental areas. There was a reduction in the warm bias by several degrees in places and the positive impact was also seen at 850 and 700 hPa. There was also significant reduction in the bias of the dew point temperature at 2 metres.

12 July 1994 Two data types were introduced into the data assimilation: temperature observations from aircraft and winds derived from the METEOSAT water vapour channel.

23 August 1994 The post-processing of 10m winds over land was changed, resulting in a more realistic representation of model winds at observing sites (IFS cycle 12R1). The negative bias of the wind speed has been significantly reduced, in particular during daytime.

6 December 1994 The 1D-Var system for the processing of cloud cleared radiance data received from NOAA satellites has been used in the Southern Hemisphere and the Tropics in addition to the Northern Hemisphere, to derive temperature and humidity data for the analysis using a variational inversion technique (IFS cycle 12R1.5).