Why does Precipitation in the South and Southwest of Iran Decrease in February Compared to Other Winter Months

Abstract

Winter precipitation in the southern part of Iran is of special importance due to its coincidence with the cultivation period and the supply of part of the water needed for agriculture. The study of 30-year monthly rainfall in the southern stations of Iran in this study and other research by the authors showed that the amount of precipitation and the number of input systems in this region in February compared to the months before and after it have decreased significantly. Moisture flux from the surrounding warm seas and on the region in the target months, the location of the Arabian anticyclone and the Mediterranean trough axis both in the whole statistical period(1986-2017)and in the sample years, the position of the subtropical jet axis in the sample years, the assumptions options were effective in changing the precipitation in three-month. The results of this study showed that spatial displacement of the anticyclone, especially at the level of 850 hPa and north and south displacement of the subtropical jet, are the most important factors in reducing precipitation in February compared to other months of the cold period of the year in the south of Iran. The subtropical jet is far from the region and shows a noticeable northward movement in February. Another phenomenon is the more shift to the west and orbital expansion of Arabian anticyclone in February compared to the other two months. This anticyclone pattern can be a serious obstacle in moisture advection and expanding the Sudanese system over the region.