一次东北冷涡暴雨的水汽输送特征和位涡分析

通过对2010年7月27~29日吉林省一次较大范围的冷涡暴雨、大暴雨过程进行诊断分析,建立了此类暴雨的天气概念模型：200 hPa呈现“两脊一槽”型,高空急流呈辐散状位于吉林省上空,急流中心最大风速≥60 m/s;500 hPa东北冷涡强烈发展,鄂海阻高稳定维持是此次强降水发生的重要天气系统,中心最大风速≥20 m/s的偏西风急流带横穿吉林省中部;850 hPa风速≥12 m/s的3条急流带在吉林省中东部地区交汇,形成低层辐合、高层辐散的气旋性涡度柱,较强的垂直上升气柱一直向上伸展到500 hPa附近,极有利于对流的发展和强降水的维持。通过计算整层水汽通量与吉林省逐6 h平均降水量的相关矢量场,结果表明：偏西、偏南及偏北3条水汽通道在吉林省中南部汇集是此次强降水发生的重要条件,暴雨落区与整层水汽通量汇合区密切相关,水汽输送以经向(南北方)水汽流入为主。暴雨期间具有较好的动力、热力及能量条件,特别是湿对流有效位能明显偏强,强降水出现在对流有效位能 (CAPE)值由极大值开始下降的过程中。干侵入是激发冷涡发生、发展的动力条件之一,≥1 PVU(位涡单位)的高位涡舌在下降的过程中,同时南移,与中部地区强降水落区自北向南移动相吻合。

Water Vapor Transport Features and Potential Vorticity Analysis of A Northeast Cold Vortex Rainstorm

Based on the diagnostic analysis of a wide range of cold vortex rainstorm and heavy rainstorm process from 27 to 29 July,2010 in Jilin Province, the conceptual model of such heavy weather was established："two ridge and one trough" type was consisted, upper-level jet was divergent and located in Jilin Province, the central maximum of jet wind speed was≥60 m/s at 200 hPa; the strong development of northeast cold vortex and the stable maintenance of Okhotsk blocking high at 500 hPa was an important weather system of the strong precipitation, the jet zone with ≥20 m/s west wind speed crossed over the central section of Jilin Province; the three jets with ≥12 m/s wind speed at 850 hPa intersected in the middle-eastern area of Jilin Province and formed the cyclonic vorticity column of low-level convergence and upper-level divergence, the strong vertical-rising gas column had been extended upward to near 500 hPa,these were very beneficial to the maintain of convection and the development of strong precipitation. By the calculation of the correlative vector field between the whole layer of water vapor flux and 6-hour average precipitation in Jilin Province, results showed that: collection of the three water vapor channels of west, south and north in the middle-southern part of Jilin Province was an important condition for the rainstorm;the rainstorm area was highly correlated to the confluence area of vertically integrated water vapor flux; the dominant direction of water vapor transport was meridional (South and North).The rainstorm was benefited from suitable dynamic, thermal and energy conditions, especially the wet Convective Available Potential Energy(CAPE) was obviously strong and the heavy precipitation occurred when the CAPE value began to fall from the maximum. Dry intrusion was one of the dynamic conditions that stimulated the occurrence and development of cold vortex; the tongue of high potential vorticity of ≥1PVU (Potential Vorticity Unit) shifted downward vertically and moved southward at the same time, corresponding to the move of heavy precipitation area from north to south in the central region.