Description of the upgrade

The following changes were implemented
  1. The parametrisation of surface fluxes at low wind speed over sea was modified by replacing the transfer co-efficients for heat and moisture in unstable conditions (free convection limit). The change has had a considerable impact on the latent heat flux which, over the Western Pacific (warm pool), can increase by up to 25 W/m2. Synoptically it primarily affects the tropical flow which becomes more realistic at lower levels (e.g. improved monsoon flow) as well as at upper levels (reduced zonal men wind error);
  2. The formulation for the convective cloud cover was modified to account for non-precipitating shallow cumuli. The effects of this change are an increase of total cloud cover (most noticeable in the trades and over the continents in daytime), a reduction of continental precipitation, and enhancement of evaporation over subtropical oceans (by 5-10 W/m2).

Implemented: 05 June 1990