A weather generator based on the European "Grosswetterlagen'

Abstract

"Down-scaling' approaches are needed in order to transform GCM climate change scenarios to appropriate scales for climate impact investigations. a statistical approach is developed based on the relationships between variations in regional climate and changes in large-scale circulation over the North Atlantic Ocean and Europe. Using the well-known classification scheme of circulation types, the European "Grosswetterlagen', a conditional climatology for different large-scale air flow patterns was calculated using long daily meteorological data sets at 3 weather stations in Germany. The coupling of flow direction and climate at a site of interest varies with season and with circulation pattern. Using long observed time series of daily surface air temperatures and precipitation, the model was calibrated and validated. Comparison of observed and simulated data demonstrated the ability of the model to adequately explain the statistical structure of the daily time series at 3 German sites. -from Author