Surface atmospheric circulation patterns and associated minimum temperatures in the Maipo and Casablanca valleys, central Chile

Abstract

This paper analyzes the influence of circulation anomalies on the magnitude of minimum air temperature (Tmin) at a daily scale in two important agricultural valleys of Chile (Maipo and Casablanca) during the period 2001– 2007. A statistical classification of synoptic fields was performed, resulting in eight circulation patterns (CPs, 84 % of explained variance). The corresponding anomalies of Tmin (ATmin) of each CP were analyzed in order to understand their synoptic-scale forcing mechanisms. Results showed a direct association between ATmin and the synoptic structure. The average weakening in sea level pressure (SLP) yields positive ATmin, while negative ATmin is associated with a strengthening in SLP. In the latter case, it was also found that a synoptic structure (10.2 % of frequency) corresponding to a migratory high-pressure system passing eastward across the Andes led to the lowest ATmin and a higher probability of frost in both valleys (22 % on average) in winter and springtime.