Cyclonicity index shows the effect of the cyclonic or anticyclonic systems in a region based on the position of synoptic systems, the cyclonicity index was defined and its frequency was investigated.Five different types of atmospheric circulation, including trough edge, trough line, unknown pattern, ridge edge and ridge line, were classified according to the geopotential elevation curvature. As a result, the daily cyclonicity index time series was created; The frequency averages of atmospheric circulation types at the 500hPa level were, respectively, 81, 20, 106, 106 and 52 days per year. The cyclonic systems (trough edge and trough line) in the 27% of days of the year and anti-cyclonic systems (ridge edge and ridge line) 43% of days of the year were presented over the region. The spatial coverage of cylonicity index is about 300 kilometers radius from the central point and covering the area around 280,000 square kilometers. ُStrong correlation was observed between cyclonicity index at two 500 and 700 hPa levels that may be interpreted as the presence of transient weather systems over the study region. Mann-Kendall test showed a significant reduction in the frequency of cyclonic systems and an increase in the frequency of anti-cyclonic systems over the study region. It may be interpreted as longer dry periods in the study region.