بررسي الگوهاي گردشي تراز 500 هكتوپاسكال جو در سال هاي كم بارش ايران

Synoptic climatology studies the relationships between the atmosphere circulation and the surface environment of a region. This study was done during low precipitation years in Iran(1983, 1985, 1987, 1989, 1990, and 1999). In order to explore the spatial and temporal variation of 500hpa flow patterns and their relationship with the precipitation of Iran , daily geopotential heights for the region 0?E to 70 ?E and 10 ?N to 60 ?N ,at 2.5 degree resolution, were analysis. A PCA analysis of geopotential heights in S-mode showed that there are seven significant map patterns. These are explaining about 93 percent of variance. The 1st of map patterns(MPl) represents latitude flow and 2,4,5,6 and 7 patterns determine ridge over Iran. Flow patterns lead air masses toward Iran which the causes low precipitation of the country.