Description of the upgrade

Changes were made in the model's physics to improve the representation of surface and planetary boundary layer processes:
  • introduction of entrainment at the top of the planetary boundary layer;
  • increased entrainment in shallow clouds;
  • modified roughness length and air-sea transfer coefficients;
  • enhancements to the parametrisation of the soil processes (four layers with prognostic variables for soil moisture and temperature plus a skin layer temperature).
The meteorological impact of these changes are:
  • an overall synoptic improvement of the predicted flow, particularly over Europe in summer;
  • a significant reduction of the warm bias in continental boundary layer during daytime in summer;
  • a large improvement of the humidity in the boundary layer, with a more realistic diurnal cycle.
The impact on the temperature in the daytime boundary layer is noticeable with a typical reduction in the warm bias at 2 metre of 2-3 degrees.
However, an increase in the cold night-time bias has been noticed. Depending on the prevailing cloud cover, the 2 metre night temperatures will, in places, be too low by several degrees.

Implemented: 04 August 1993