Extreme values of air temperature in Poland according to different atmospheric circulation classifications

The paper focuses on synoptic and climate analysis with the application of circulation types based on six classification schemes, both subjective and objective. The principal goal of the study was to determine circulation types with respect to the occurrence of extreme values of air temperature. A comparison between different available classifications was also performed. Maximum and minimum daily temperatures for the 56-year study period (1951-2006) were used in the analysis. The necessary data series were obtained from 61 weather stations, relatively well spaced across Poland. Each series was checked for homogeneity and evaluated. Detailed calculations were performed for the summer (June-August) and winter (December-February) seasons. Extreme values were selected with respect to probability distribution bases. The top and bottom 5% were used for further analysis. Calculations of extreme values for particular types and classifications were the main phase of analysis. All extreme temperature values were analyzed for each type. This enabled the creation of histograms presenting types producing the highest number of particular extremes. The study showed that circulation types with an anticyclonic ridge were the most important for extremely hot days in the summer, while extremely low temperatures in the winter were usually associated with anticyclonic types with an easterly airflow. A special effort was made to identify the classification scheme yielding the best accuracy in evaluating extremes. (C) 2010 Elsevier Ltd. All rights reserved.