1997 summary of changes

21 January 1997 Model cycle 15R8 was introduced. This cycle corrects an error affecting the degree of balance between the mass and wind analyses.

13 May 1997 A new version of the optional project wave models was implemented. It consisted of a change in the representation of the wave spectrum to solve the excessive shadowing effect behind islands that was experienced before. This allowed the reintroduction of islands that were deliberately omitted in the previous version.

Please see "Operational implementation of the high resolution Ocean Wave model" the ECMWF Newsletter describing these changes

14 May 1997 Several modifications to the 3D-Var data assimilation system were implemented (model cycle 16r2):

1. two modifications of the forecast error penalty function (Jb). One allows the use of a refined balance constraint, with most impact in the tropics (better fit of the analysis to the observations). The result is also slightly positive in terms of forecast scores. The other modification is in the formulation of the representativeness error growth used for the assimilation of asynoptic data. The errors are now supposed to saturate at levels that are fully varying with space and this was shown to have a positive impact both on the analysis increments and on the data quality control;

2. several modifications in the way the TOVS data are used (quality control, modification of the tropical bias correction in line with the Jb re-formulation);

3. a restriction of the dynamic initialisation to the small scales.

27 August 1997 A number of modifications were made, mostly concerning the use of satellite data (model cycle 16r3):

1. a revision of the use of TOVS radiances including the simplification and improvement of bias corrections. SATEM retrievals were replaced by the use of radiances above 100 hPa while H1RS12 were introduced both over sea and land;

2. some quality control modifications with most impact on the way ERS-2 wind retrievals are handled.

Revisions were also made to the ocean albedo and to the momentum transport representation in the convection scheme. A correction was applied to computations of saturation vapour pressure with effect mainly in very cold conditions.

Please see "Influence of observations on the operational ECMWF system" in ECMWF Newsletter No. 76

11 November 1997 A modification was made to allow the assimilation of the new RTOVS format for NOAA-14 radiances (model cycle 18r1). NOAA-11 RTOVS have been assimilated since 1 December.

25 November 1997 The first version of a four-dimensional variational data assimilation system (4D-Var) was introduced. It is based on an evolution of the previous 3D-Var system with a 6-hour cycling.

Please see "The operational implementation of 4D-Var" the ECMWF Newsletter No.78

16 December 1997 A number of changes to the physical parametrization scheme were introduced (model cycle 18r3):

1. A modification in the treatment of the water vapour absorption in the long-wave part of the radiation scheme;

2. A new method of moisture convergence closure;

3. A new treatment in the ice fall-out in the cloud scheme.

Please see "Introduction of revised parametrizations of physical processes into the IFS" in
the ECMWF Newsletter No.79