Mesoscale precipitation and temperature regimes in Sardinia (Italy) and their related synoptic circulation

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 s everal distance measures. Thirty years of daily data, for the period rangin g from 1951 to 1980 for the 114 stations with precipitation and 20 with tem perature, were used in the study. In order to retrieve homogeneous clusters, non-hierarchical methods were fo und to be more effective and the use of a correlation-like distance was mor e effective for precipitation. To discriminate between the different cluste rs, the corresponding mean mass fields for the 500 hPa height and sea level pressure were used and an analysis of synoptic situations linked to mesosc ale regimes was performed. The results show that at least two mean surface patterns exist corresponding to clearly different synoptic situations. Neve rtheless, physical considerations led us to consider three distinct cluster s, two of which correspond to specific synoptic circulations with slight, b ut meteorologically significant, differences.