Rimbu95 Rimbu, N. and S. Stefan, 1995: A diagnostic study of the meteorological fields simulated with the UKMO general circulation model. Abstracts of the First International AMIP Scientific Conference, Monterey, California, 47.

This paper presents the preliminary results of the intercomparison study of some General Circulation Models from Europe, initiated by CEC Medium Term Climate Variability Project. We have dealt with:

a) The particular phenomenological aspects of the simulation and performance of the UKMO model. The area under study was the Atlantic-European region.

b) Spatial and temporal characteristics of the meteorological anomalies using empirical orthogonal functions (EOF). The data available were the monthly means for the AMIP period (1979-1988) as model outputs and monthly means averaged over 7 years (1987-1993) as climatological data for the following meteorological fields: sea level pressure, geopotential height at 1000, 850, 250 hPa, median and zonal wind at 1000 and 500 hPa. We have compared the simulated fields to climatological fields for winter (DJF) and summer (JJA).

The results of our analysis for the winter season show a good agreement between the simulated and the observed fields.
Some remarks include:

In the field of sea level pressure,

  • the simulated Icelandic low is shallower than the climatological low but both is located at the same position 

  • the center of the simulated anticyclone in the Azores is located to the southeast of the center of the climatological similar pattern namely in the N-W of Africa. The difference between the simulated and the climatological patterns can be explained by the inability of the model to fit the characteristics of the land and the ocean.

  • both the model and the climatological data emphasize slack mean pressure gradients over Eastern Europe

In the geopotential field of the middle troposphere,
  • the ridge-trough system over the Atlantic-European region appears both in the simulated and climatological data but the model slightly moves this system eastward.

  • the averaged circulation at 500 hPa in both observed and modelled atmosphere is characterized by a trough over Eastern Europe.
The atmosphere wind fields vary considerable with location and the season:
  • the flow is predominantly zonal from west to east over the Europe having the same magnitude both in the model and in the climatological data 

  • a great deal of variability in the wind field is associated with the relaxation of the ridge-trough system at the 500 hPa level.

The EOF analysis of the geopotential heights at 500 and 1000 hPa for the UKMO model for winter identifies in the field of the first eigenvector the principal patterns corresponding to the North Atlantic Oscillation (NAO) and the Pacific-North American Oscillation (PNA). The first eigenvalue represents 23% to 32% from the variance for the 500 and 1000 hPa, respectively.