Climatic Characteristics Of Tashkent Vortex And Its Influence On Rainfall In Southern XinJiang

The Tashkent vortex is one of the major weather systems for the Southern XinJiang. In this paper, we present a definition of Tashkent vortex, and the statistical measurement is determined through synoptic and statistical method by using the NCEP/NCAR reanalysis data in1971-2010.Then the characteristics of spatial and temporal distribution, duration and moving track of Tashkent vortex in1971-2010are investigated by using Tashkent vortex data sets that obtained from the automatic recognition by computer. Besides, the analysis of the influence on precipitation in Southern XinJiang that caused by Tashkent vortex with different general circulation and water vapor transport are attempted with comparative of weather cases.The analyzed results of Tashkent vortex in1971-2010are as follows:There are7.95times Tashkent vortex processes per year in1971-2010. The average life of mature Tashkent vortexes is3.1days, and only13.5%surpass4days. The frequency of Tashkent vortex peaked at4-6and9-10month, and it most in May, followed by October and June. The decadal variations of frequency of Tashkent vortex show as parabola. Frequency of Tashkent vortex increases from78in1970s to83in1980s, then it decreases gradually after1980s. Annual frequency changes of Tashkent vortex have significant oscillation with7a period, as well as the characteristics of sub-oscillation with12-14a period. There are two high-frequency regions of Tashkent vortex, the one is67.5°E,40.0°N, the other is72.5°E,35.0°N. The vast majority of Tashkent vortexes are eastward and its proportion reach84%of the total. At the same time, the proportion of Tashkent vortexes that moving westward is5.7%. The rate of precipitation vortex is23.3%, which is highest in summer (41.2%).Though the analysis and comparison of Tashkent vortex cases, it is founded that there is different precipitation intensity in Southern XinJiang caused by the vortex with different general circulation and water vapor transport. While significant precipitation accrued in Southern XinJiang, circulation appears as trough in Southern XinJiang on100hPa and500hPa and subtropical jet lie in south of35°N with its jet stream core lie in west of85°E on200hPa and ridge in East China on700hPa. At the same time, the east jet stream lies in Southern XinJiang. On the contrary, circulation appears as Southern XinJiang is controlled by South Asia high on100hPa and ridge in 500hPa. The subtropical jet and its jet stream core lie in Southern XinJiang on200hPa and the east wind is weak on700hPa in Southern XinJiang. When circulation appear as former, the vapor over Arabian Sea will be transported to Southern XinJiang through relay transport mechanism with the maintenance of Arabian Sea tropical cyclone and strong west jet stream in north India, that will cause heavy rain in Southern XinJiang.