1993 summary of changes

1 February 1993 Changes were introduced to the horizontal diffusion and to the cloud-radiation scheme (cycle 46), inclusion of shortwave optical properties for ice and mixed phase clouds, and revision to the clear-sky absorption coefficients.

21 April 1993 Cycle 47

4 August 1993 Changes were made in the model's physics to improve the representation of surface and planetary boundary layer processes (model cycle 48, cycle 47 was a technical change):

  • 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.

 

5 October 1993 A change to the boundary layer parametrisation was introduced, further to the change of 4 August 1993 (cycle 49). The profiles of 2 metre temperature in stable conditions were revised to reduce the coupling between the skin temperature and the temperature of the lowest model levels. The cold bias of the predicted night-time temperature was reduced by this change.

11 November 1993 The pre-processing was modified to correct radiosonde observations for systematic biases prior to their use in the data assimilation. The correction is applied to the radiosonde stations which present a significant bias in geopotential height due to radiative effects, on the sonde (long wave cooling and short wave heating, mainly in the stratosphere).

 

Cycle changes

Please note

Prior to 2006 information on cycle upgrades has been migrated from the old website to the new website "as is". The information has not been reviewed during the migration.