CLASSIFICATION OF CIRCULATION TYPES OVER BULGARIA: METHOD DESCRIPTION, FREQUENCY, VARIABILITY AND TREND ANALYSIS

A classification of circulation types for the region of Bulgaria is made on daily basis using subjective (manual) approach, covering 56-year period (1961-2016). The classification is based on mean sea level pressure (MSLP) and 500hPa data from (20th century reanalysis at 00, 06, 12 and 18UTC time) within the area of 30? - 75?N and 20?W - 50? E. 13 types at 500hPa (8 cyclonic and 5 anticyclonic) and 16 types at MSLP (8 cyclonic, 6 anticyclonic and 2 low gradient) are differentiated, described and visualized with examples. The work starts with brief summary of other well-known classifications of the circulation in northern hemisphere and in different parts of Europe. The frequency distribution of circulation types, on the seasonal, annual and decadal time scale are presented and analyzed. Annual distribution and annual trend analyses of the circulation types are described. Finally, additional comments are done about the annual and seasonal variability, concerning some circulation types with greater influence on the territory of Bulgaria.