عنوان مقاله [English]
نویسندگان [English]چکیده [English]
The various atmospheric circulation patterns are caused the different conditions of weather; for example, the frequency changes of occurrence of atmospheric circulation patterns weather types are caused the precipitation patterns variations, therefore, studies on weather types can used as a criterion for analysis of precipitation patterns variations. Precipitation variability is one of the important factors which controls natural and economical systems. This effect is more significant in arid and semi-arid regions such as Iran. This paper, studied relation between circulation patterns and ENSO index. In order to classification of circulation patterns, the data of 500 hpa geopotential height and sea level pressure were taken from NCEP data center at the statistical period of 1961-2003. For classification of daily weather types, it is used principle component analysis and clustering method. Finally, 8 weather types were recognized for Iran on winter season time. In order to recognition of relation between frequency of various weather types and warm and cold phases of ENSO, the monthly data provided from NCEP and then frequency of weather types were calculated in warm, cold, and neutral phases. Conclusions reveal that Mediterranean low-pressure, South polar low-pressure, Eastern high-pressure, Northern high- pressure and Eastern European high - pressure and also joining Siberian high - pressure with the European high - pressure in the El Nino phase have more frequencies, Whereas occurrence frequencies of the Siberian high - pressure and central high - pressure systems are more at the La Nina periods.