14 January 2003 Introduction of Cycle 25r4. This version includes changes to many aspects of the data assimilation and forecasting system:
- Revised multi-incremental (T95/T159) 4D-Var algorithm, including interpolation of high resolution to low resolution trajectory
- Use of Omega-equation and non-linear balance in the Jb, together with statistics from ensembles of 4D-Var assimilations
- Revised Jc (more selective to gravity waves)
- Assimilation of GOES WV radiances, MODIS winds, more HIRS channels and SAR ocean-wave data
- Direct assimilation of SSM/I radiances in 4D-Var
- Improved cloud-scheme numerics, cleaner code, and bug fixes;
- Revised cloud physics
- Revised convection scheme with new type and cloud top/base algorithms; checks all levels up to 700hPa for initiation of deep convection.
In addition, the RNORM parameter scaling EPS initial perturbations was reduced from 2.0 to 1.6 as a consequence of the data assimilation statistics retuning. This effectively keeps the EPS spread at the same level as in the current operational version.
The impact of these changes has been found to be meteorologically positive during the test period over a wide range of areas and parameters. Tests conducted during the summer have shown a clear reduction of the forecast errors generated over North America and advected towards Europe at this time of the year. The new model version removes convective potential instability more effectively and realistically, as was found in several case studies. Stratosphere forecasts have also been improved.
The new model cycle is used throughout the Centre's forecast suites, the T511 main run, the EPS and the BC Optional Project. The atmospheric model identification number in the GRIB headers changed from 201 to 202.
Model numbers for the Global wave model (113) and the European waters wave model (213) remained unchanged.