新疆夏季两例塔什干低涡天气过程对比分析

利用NCEP1°×1°再分析资料,对新疆夏季两次塔什干低涡天气过程进行对比分析,从天气尺度环流系统配置、动力和水汽输送的角度探讨造成南疆不同降水强度的塔什干低涡特征差异。结果表明:当南亚高压中心位于70°E,南疆位于200 hPa急流轴出口辐散区,500 hPa塔什干低涡东移携带强西南气流时,700 hPa盆地有显著东风急流,偏西地区中低层切变辐合长时间维持,同时通过接力输送的阿拉伯海水汽与中低层东风急流携带的水汽强烈辐合,导致大范围暴雨,高层正MPV1、负MPV2向下伸展,中低层不稳定性、斜压性增强,配合700 hPa以下负MPV1、正MPV2激发垂直涡度增长,对流性降水加强;当南亚高压中心始终维持偏东(90°E),南疆位于200 hPa急流轴上,500 hPa里海脊和新疆东部高压脊势力相当时,塔什干低涡减弱为槽影响南疆,700 hPa南疆盆地东风气流弱且位置偏西,南疆地区无明显高层辐散、中低层切变辐合,不利于垂直上升运动的发展和水汽的集中辐合,难以造成显著降水。

Comparative Analysis of The Two Cases of Tashkent vortex weather processes in summer in Xinjiang

Based on the NCEP 1°×1°reanalysis data, the characteristics of the weather scale circulation , dynamic and water vapor transmission of the two cases of Tashkent vortex weather processes were contrasted and analyzed. The results showed that: during South Asia High center located at 70°E, the south Xinjiang Basin was in the left ahead of the 200 hPa jet export zone ,the maintenance of 500 hPa strong southwest airflow and significant easterly jet stream in the southern xinjiang basin of 700hPa maked sure that the middle and low level shear line and convergence maintained. At the same time, the water vapor in the Arabian sea transmitted by relay transmission strongly converged with the water vapor carried by the middle and lower easterly jet stream, resulting in large-scale rainstorm. The downward extension of the negative hygroscopic tongue in the upper layer and the increase of the baroclinic pressure in the lower and middle atmosphere maked convective precipitation more intense. But as the center of South Asia High maintained over 90 °E ,200hPa jet over southern Xinjiang ,the lower vortices are reduced into slots to enter the southern border. Over south Xinjiang Basin , if the easterly airflow of 700 hPa was weaker and located further west ,and high level divergence and low level convergence were weaker, it is not conducive to the development of vertical upward movement and the convergence of water vapor. As a result, it was difficult to caused precipitation, even though the influencing system was a Tashkent vortex.