Identification of the effective jet stream patterns in the heavy Precipitation of the cold season in the southern half of Iran

The purpose of this research is to identify the relationship between different types and configurations of the jet stream with heavy and pervasive rainfall southern half of Iran. For this purpose, daily rainfall data of the cold season (December to March) during the 1970 to 2014 period was obtained from the country's meteorological organization. Then, considering the two conditions of learning over 50% and the rainfall of more than 95% percentile of each station, 61 days of heavy and pervasive rainfall were selected for the synoptic analysis. upper tropospheric data also includes zonal and meridian wind, Geopotential Height, sea level pressure, omega, and specially humidity, which was obtained with a spatial resulotion of 2/5 * 2/5 arc of the center of the American Weather Forecast. Then, by using the principal component analysis on geopotential height data of 500 hPa in the 61 days of selected precipitation, 12 factors, which explain more than 90% of the data diffraction, were extracted. By applying the cluster analysis with Ward method on the factor scores, the four patterns influencing the arrangement of the jet streams were identified. The results showed that subtropical jet stream with Reinforcement surface Convergence and divergence field at high levels And consequently the development of surface low pressure And mid-tropospheric trough levels, It plays an important role in the incidence of heavy and heavy rainfall in the southern half of the country And its interactions with the polar jet stream lead to the most severe and widespread rainfall days in the region. In the studied patterns, the jet stream deployment from northern Arabia to northern part of Iran with zonal and meridian curvature And the equilibrium of the left-hand side of the output of the jet stream with low pressure sea level and half-eastern troposphere middle level trough, The hot and humid air brings the Red Sea, Persian Gulf and Arabian Sea to the southern half of the country.