Description of the upgrade

A high resolution analysis and forecasting system at T213 31 levels was put into operations. In addition to the change of resolution, the new model includes the following aspects:
  • the Gaussian grid used for the computation of the physics is now a reduced Gaussian grid, i.e. the number of grid points along a latitude circle decreases towards the poles in order that the spacing of the points be approximately 60 km on the whole globe. The effective resolution in the free atmosphere is around 100 km. at half wavelength;
  • several changes are made to the dynamics of the model, including use of a semi-Lagrangian advection scheme and modified horizontal diffusion. A change in the link between the dynamics and the parametrisation of vertical diffusion is expected to reduce the surface wind by about 3% over sea and about 10-15% over land;
  • a new version of the cloud scheme, mainly to allow the stratiform clouds to form in any number of layers instead of the three layers in the previous version.

Implemented: 17 September 1991