Circulation types and extreme temperature changes in Greece

We examined changes in extreme temperature over the Greek area in relation to the geopotential thickness field (1000 to 500 hPa). Daily maximum and minimum temperature series from 20 Greek stations evenly distributed over Greece were used for the period 1958-2000. The atmospheric circulation over the Greek area was classified with the aid of a calendar of daily circulation types based on the geopotential thickness field of 1000 to 500 hPa for the same period using daily NCEP and HadAM3P datasets. There was a general increase in frequency of anticyclonic circulation types and a decrease in frequency of cyclonic types. In addition, there was an overall interannual increase (decrease) in maximum (minimum) extreme temperatures over the Greek area, with spatial and seasonal variations. The investigation of the temperature anomalies corresponding to each circulation type, along with the trends of the former, revealed that the increase in frequency of the anticyclonic 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 decreasing minimum temperatures in the central and SW Greek area cannot only be interpreted by changes in frequency of circulation types. A statistical downscaling model for simulating temperature changes over Greece (both for NCEP and HadAM3P datasets) was developed following a circulation-type approach. This demonstrated high correspondence with the observed extreme temperature values in all seasons, with only slightly lower year-to-year variability.