Description of the upgrade

The following changes were implemented:
  1. A reduction of the run-off of convective rain, increasing the amount of water available to wet the soil. The implied change of energy balance at the surface increases the latent heat flux at the expense of the sensible heat flux, giving a decrease in the surface and near-surface air temperature. This should significantly reduce the warm bias of the 2m temperature over continental areas during the day.
  2. Modifications to the treatment of snow covered surfaces:
    • the thermal budget of the snow is modified to take into account the effect of shade from vegetation;
    • the albedo of the snow is no longer only dependent on snow depth; the new formulation also takes into account masking by vegetation, the effects of temperature and the presence of ice dew.
  3. The overall effect is to decrease the albedo of the snow covered areas.
  4. A modification to the model pressure-gradient calculation and a change in the calculation of pressure level geopotential heights by the model post-processing and in the first-guess for the analysis.
  5. Modifications to the convection scheme, mainly to the treatment of cloud processes at detrainment levels for convective clouds, to prevent a spurious moistening at cloud tops which was noticeable over the subtropical oceans in connection with shallow convection.

Implemented: 16 May 1990