Seasonal Location and Frequency of Cyclonic Trackes in Wet Periods of Midwest of Iran

This research that was made on 66 cyclones in wet periods of Midwest of Iran in a given period (1973-2003) shows that in intense wet periods, cyclogensis centers of Mediterranean sea, Sudan, Red sea and Mesopotamia were severely active and have been very effective in rainfall of study area. Such systems in general, with respect to dominant synoptic patterns, enters into study area from three main tracks: A) From west and central Mediterranean cyclogensis centers and also north of Cyprus island toward northeast of study area. These systems with reinforcing in east of Caspian Sea follow to Aral's lake. B) From cyclogenesis area of Cyprus and north of Mesopotamia toward study area in east of Zagros ranges extended to northeast and Aral's lake. C) From Cyprus and north part of Red sea and Mesopotamia toward north Persian Gulf and by passing from Zagros ranges extended to southeast and northeast of Iran. Cyclone's frequency and tracks have change very much in autumn because of variation in equatorward motion of STHP. Winter cyclones have long duration than the other seasons and their central pressures are higher than spring and lower than autumn ones. In addition, these cyclones- because of their dynamic conditions- have longer tracks. Although spring's cyclonic tracks have more variety, but with slight change two marked tracks of winter are also shown in spring.