Abstract

Atmosphere circulation patterns have an important role in appearance of natural events. For this purpose, in the present study in order to identify the atmosphere circulation patterns which cause humid periods, the principle components analysis method and cluster analysis were used. Therefore by emphasis on peripheral circulation approach, wet periods during a 30 years statistic period (1982-2011) in 6 synoptic stations in Kerman, Yazd and Isfahan province which have long term common statistic period were calculated using standard precipitation index. The findings of principle component analysis showed that by eight components it is possible to explain 94 percent of the variations in geo-potential height data. Therefore, the first component with 62.3 percent appearance shows the dominance of polar and Siberia high pressure in cold period of the year, and the remaining components show atmosphere instabilities which penetrate the region from Mediterranean sea, Black sea and Red sea. The results of cluster inspections show that there are two patterns with 28 percent frequency and 15 percent probability of precipitation in the region. Therefore, the circulation pattern of middle level of the atmosphere shows that by establishment of a deep trough at the east of Mediterranean sea and red sea and locating the east of trough on the researched area, and simultaneously a low pressure centre become dominant at the sea level on the region which cause precipitation event. This arrangement of circulation pattern causes Iran to exit from drought.

Keywords: Cluster analysis; Principle component analysis; Synoptic patterns; Wet periods