Revisions during 2001

17 January 2001 Due to the failure of the ERS-2 navigation instruments, both the ambiguous surface winds and the altimeter data became unavailable.

5 February 2001 The amplitude of the EPS initial perturbations was upscaled by a factor two.This rescaling was linked to the data-assimilation changes introduced with Cy22r3 in June 2000 which resulted in a lack of spread.

6 March 2001 The ERS-2 altimeter data were switched on again in the oceanic-waves data assimilation. The ERS-2 winds remain unavailable.

12 June 2001 Introduction of Cy23r4. This version includes the following modifications:

1. several changes in the use of satellite data over land and sea ice (more AMSU data and use of skin temperature rather than upper-layer soil temperature in processing radiances);

2. radiation parametrization routines are called on an hourly (instead of 3-hourly) basis during the data assimilation;

3. the time integration of the surface skin temperature over land has been improved;

4. the horizontal diffusion on vorticity has been increased to bring it in line with that applied to divergence and temperature without any noticeable impact on the forecast fields;

5. an improved ozone model developed by Meteo France has been introduced with a new parametrization of the destruction of ozone by heterogeneous chemical processes.