عنوان مقاله [English]
نویسندگان [English]چکیده [English]
The present research has studied the synoptic of cyclonic activities at different levels of Iran’s atmosphere. The cyclone-genesis zones and its movement paths can be identified by several algorithms. This research has performed to identify the temporal and spatial conditions of effective cyclones on Iran climate on seasonal and monthly scales. To identify the Cyclones, 6hours data of geo potential heights (HGT) for 1000,925, 850, 700, and 500 hPa levels were extracted from NCEP/NCAR database for coordinates of 30◦west up to 80◦ east and 0◦ - 80◦ north for year 1990. The statistical analysis of cyclones in several levels of atmosphere showed that in 1990, maximum number of cyclones occurred in 500 hPa level and the least frequencies occurred in 850 hPa that have only 990 cyclones. Generally in 500 and 700 hPa, the peak of Mediterranean cyclones activities occurred in December to February. In cold period, a cyclone- genesis center has been located in Italy. The second cyclone- genesis center is extended from Greece up to Cypress. In winter, Italian cyclone- genesis centers are transferred to eastern half of Mediterranean Sea, on Cypress, Syria and Turkey. These locations comprise the main cyclone- genesis centers in winter. Generally it seems that the expanding limit of dynamic cyclones are from 500 to 700 hp level. Only if the cyclone is very strong it can be seen at levels lower than 700 hPa.