شناسايي و تجزيه و تحليل الگوهاي تراز مياني جو در سال هاي پربارش ايران

500 hpa Circulation patterns associated with rainy years of Iran

In order to explore the spatial and temporal variation of 500hpa circulatiorpatterns and their relationship with the rainy years of Iran (1974, 1976, 1982, 198f.and 1992). daily geopotential heights for the region 00 E to 70 0 E and looN to 60 0 N ,at 2.5 degree Y Abstract resolution, were analysized. A PCA analysis of geopotential heights in S-mode showed that there are seven significant circulation patterns. These patterns explain about 93 percent of variance. The 1sf circulation pattern represents a deep trough over Iraq, and Iran is located in its eastern part. Circulation pattern 2 represents a trough over the Mediterranean Sea. Circulation pattern 3 represents shallow trough over the Iran. Circulation pattern 4, which its representative day is December 21st 1982 indicates a trough over the Cyprus. A rather shallow trough dominates over Iran. Circulation pattern 5 represents shallow trough over the Black sea which probably affected north and northwest of Iran. The sixth circulation pattern is a representative trough over the Caspian Sea which extends toward the Black Sea and even the Mediterranean Sea. The seventh circulation pattern represents the disposition of a high over Iraq that extends all over Iran. Some of These circulation patterns lead air masses to Iran which causes years with high precipitation.