Circulation types and extreme temperature changes in Greece

Abstract

ABSTRACT: We examined changes in extreme temperature over the Greek area in relation to thegeopotential thickness field (1000 to 500 hPa). Daily maximum and minimum temperature series from20 Greek stations evenly distributed over Greece were used for the period 1958–2000. The atmos-pheric circulation over the Greek area was classified with the aid of a calendar of daily circulationtypes based on the geopotential thickness field of 1000 to 500 hPa for the same period using dailyNCEP and HadAM3P datasets. There was a general increase in frequency of anticyclonic circulationtypes and a decrease in frequency of cyclonic types. In addition, there was an overall interannualincrease (decrease) in maximum (minimum) extreme temperatures over the Greek area, with spatialand seasonal variations. The investigation of the temperature anomalies corresponding to each circu-lation type, along with the trends of the former, revealed that the increase in frequency of the anticy-clonic types, which form positive anomalies, and their positive trends in the majority of the stations,can explain the upward trend of maximum temperature in summer. In contrast, the trend of decreas-ing minimum temperatures in the central and SW Greek area cannot only be interpreted by changesin frequency of circulation types. A statistical downscaling model for simulating temperature changesover Greece (both for NCEP and HadAM3P datasets) was developed following a circulation-typeapproach. This demonstrated high correspondence with the observed extreme temperature values inall seasons, with only slightly lower year-to-year variability.KEY WORDS: Greece · Trend analysis · Extreme temperature · Circulation types · Multipleregression · Downscaling · GCM