Revisions during 2000

11 April 2000 Introduction of Cy22r1. This new version of the model is a minor upgrade including:

1. a revised use of SSM/I radiance including a bias correction and preventing the assimilation of radiances where precipitation occurs; both satellites (DMSP-13 and 14) are now used;

2. a modification of the assimilation of humidity in the stratosphere that was moistening unrealistically since the last model change (12 October 1999);

3. use of coastal ship and buoy winds in the extratropical Southern Hemisphere;

4. relaxed quality control of dropsondes

5. implementation of Full-Pos

27 June 2000 Introduction of Cy22r3.This new version includes:

1. new parametrization schemes for the land surface, lying snow and sea-ice;

2. new (RRTM) long wave radiation scheme;

3. improved ozone model;

4. use more TOVS/ATOVS data (HIRS-12, AMSU-14; less constraint on AMSU-8; more off-nadir data)

5. revised snow analysis;

6. revised observation and background error variances;

7. use of buoys platform heights;

8. digital filter for gravity wave constraint.

12 September 2000 The data assimilation procedure moved from 6-hour to 12-hour cycling. 4D-Var now processes the observations in 12-hour sets, spanning 03 -15 UTC for the 12 UTC analysis, and 15 - 03 UTC for the 00 UTC analysis. Surface analyses still run every six hours. Analysis fields are still archived every six hours. Other changes included in this model version are :

• use of more accurate background trajectory in 4D-Var, thanks to an improved interpolation procedure, the use of the prognostic cloud scheme and first-guess cloud fields;
• change to the 4D-Var incremental formulation by which the low-resolution increment is added to the high-resolution trajectory at analysis time (00 UTC and 12 UTC), instead of at the start of the 4D-Var window;
• new quality-control step that prevents the use of observations that the incremental formulation of 4D-Var cannot handle correctly;
• resetting of the stratospheric ozone and switching off of the multivariate coupling between ozone and vorticity;
• monitoring of TOVS radiances in cloudy areas.

21 November 2000 The model resolution was upgraded from TL319 to TL511 resolution in the deterministic mode, and from TL159 to TL255 in the ensemble mode (EPS). This is roughly a reduction in grid size from 60 to 40km (deterministic) and from 120 to 80km (EPS). Vertical resolution remains unchanged in all model configurations. Other changes included in this model version are:

• the data assimilation now runs its minimization (inner loop) at TL159 (was T63 previously) using new semi-Lagrangian tangent linear and adjoint codes.
• the wave model in the TL511 deterministic model continues to run at approximately 55 km horizontal resolution with an increase in spectral information from 12 to 24 directions and from 25 to 30 frequencies. The wave model in the EPS will run in shallow-water mode with an increased horizontal resolution of approximately 110 km with 12 directions and 25 frequencies (no change). The European-waters model continues to run at approximately 28 km with an increase in spectral information from 25 to 30 frequencies, while the number of direction remains at 24.

An article from the ECMWF Newsletter describing these changes is given in pdf (332 KB) file.

Note:

ECMWF has issued the following warning:

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.