Automatic classification of circulation types in Greece: methodology, description, frequency, variability and trend analysis

 An automatic classification of circulation types is developed using spatial method of topology and geometry over a 40-year period (1958–1997) for Greece. The classification is based on MSLP and 500 hPa gridded data (NCEP reanalysis data at 00, 06, 12 and 18 and mean daily data, φ = 2.5 and λ = 2.5°) within the area of 20°–65° N and 20° W–50° E. At beginning, the adopted method is analysed. Then, the 20 circulation types (6 anticyclonic, 8 cyclonic, 2 mixed and 4 special types) are analysed and described. The frequency distributions of circulation types, on the seasonal and annual time scale, are analysed. Finally, the annual distribution and the annual trend of the circulation types are described.