Mesoscale Precipitation and Temperature Regimes in Sardinia (Italy) and their Related Synoptic Circulation

Summary This paper describes an attempt to define mesoscale daily precipitation and temperature regimes over Sardinia and their relation to different synoptic patterns. In order to address this task an extensive Cluster Analysis was performed on the whole data set using a number of methods, each including several distance measures. Thirty years of daily data, for the period ranging from 1951 to 1980 for the 114 stations with precipitation and 20 with temperature, were used in the study. In order to retrieve homogeneous clusters, non-hierarchical methods were found to be more effective and the use of a correlation-like distance was more effective for precipitation. To discriminate between the different clusters, the corresponding mean mass fields for the 500 hPa height and sea level pressure were used and an analysis of synoptic situations linked to mesoscale regimes was performed. The results show that at least two mean surface patterns exist corresponding to clearly different synoptic situations. Nevertheless, physical considerations led us to consider three distinct clusters, two of which correspond to specific synoptic circulations with slight, but meteorologically significant, differences. Received November 28, 1997 Revised October 1, 1998