Performance of the general circulation HadAM3P model in simulating circulation types over the Mediterranean region

The capability of the general circulation model(GCM) Hadley Center atmospheric general circulation model 3P (HadAM3P) to reproduce the mean pattern and the frequency of circulation types concerning the 500 hPa geopotential height fields and 1000-500 hPa thickness fields over Europe and the Mediterranean region are evaluated against the NCEP/NCAR dataset for the period 1960-1990. Daily catalogues of the circulation types describing the regional circulation over Greece at the 500 hPa and 1000-500 hPa thickness fields are constructed based on the two datasets, and the corresponding seasonal frequencies are also estimated. The evaluation is performed for the mean seasonal fields of the two parameters, as well as for those derived for each circulation type separately. It is demonstrated that the HadAM3P model generally succeeds in reproducing the two fields over the examined area, while their seasonal variability is underestimated. The mean patterns of the circulation types are well represented by the model but the seasonal simulated frequencies of the circulation types are not in good agreement with the national centers for environmental predictions (NCEP) ones. The systematic errors of the frequency estimation and the variability in some anticyclonic or cyclonic types should be considered seriously, because it can introduce some degree of uncertainty in the results of a downscaling method based on a circulation type approach. Nevertheless, the links between the precipitation, temperature and circulation types frequency seem to hold in the GCMs. It is therefore safe to use the frequencies of circulation types as predictor in a downscaling technique in order to obtain future precipitation and temperature. Copyright (c) 2007 Royal Meteorological Society.