Diagnostic Analysis And Cause Study Of Heavy Rainfall Events Over Shali River Area

The shali river area locates central part in Henan,belonging to one part of river valley in Huaihe.Because the heavy rainfall occurrence is multifarious,usually resulting in the flood of flood inside the river valley and river valley in Huaihe.In order to recognize the heavy rainfall of the valley and finding out rule and cause of heavy rainfall,this text makes use of the rainfall from June to August in 1971 and 2006,combining the hydrology data,in carrying on statistics analytical foundation to the weather characteristic,heavy rainfall and the characteristics of the flood of the shali river area.With the shali river area continuously appear of two heavy rainfall events in July of 2007 for example,based on the data from the conventional and intensive observation,satellite cloud pictures and NCEP 1°×1°6h interval reanalysis data,the circulation background,synoptic weather systems and physical quantity of synoptic meteorology,dynamics and thermodynamics of two heavy rainfall events are diagnosed and analyzed detailedly.The common data analyses show that the circulation background and synoptic weather systems both belong to the typical heavy rainfall characteristic.The JUL-05 heavy rainfall event was caused by the low-level jet foundation in front of the trough and the northwest of the subtropical high over the west Pacific.At the same time,there was an upper-level jet.In the intersection region of the upper-level jet and the lower-level jet,the meso-scale systems grew into MCC.The center of strong convective which was distinguished by T_BBvalue(T_BB＜200K)was corresponding to the rainfall center.With the lower-level shear steadily maintaining,the strong up-ward vertical appeared.Because of the cold atmosphere coming,the unstable energy was released and the heavy rainfall event occurred.The JUL-14 heavy rainfall event was caused by the leading of the southwest air current in front of the trough at 500hPa,and the southwest vortex moved alone the lower-level shear,which made the heavy rainfall event.The dynamical and thermodynamic quantities show that the dynamical condition of the heavy rainfall in JUL-05 is more favorable than that condition in JUL-14.There was a lot of unstable energy in JUL-05 and the middle-level atmosphere was convectively unstable,at that time the heavy rainfall lied in the center ofθse.The middle-level atmosphere was convectively stable and the heavy rainfall in JUL-14 lied in theθse dense zone.There was only one water vapor channel from Bengal Bay to the south alongshore mainly depending on water vapor convergence at middle-lower level in JUL-05.But in JUL-14,there were two water vapor channels from Bengal Bay and Donghai,water vapor concentrated at boundary level.The calculated result of the vertical helicity shows that the JUL-14 heavy rainfall event is fully positive vertical helicity from the lower-level to the upper-level.But the vertical helicity in JUL-5 displayed a positive region at lower-level and a negative one at upper-level,whose dynamic condition was more beneficial to the occurrence of the heavy rainfall.In addition,the movement direction and intensity transformation of the positive center of the vertical helicity at 700hPa matched the heavy rainfall centers quit well.The diagnosis analysis of moist potential vorticity indicates that the lower-level atmosphere of JUL-5 heavy rainfall event is not only convectively unstable but also symmetrically unstable,which was favorable for the development of vertical and slantwise convection.Heavy rainfall was over when the unstable energy was released.However,In JUL-14,the lower-level atmosphere was convectively stable,but the border-level atmosphere was convectively unstable.In the meantime,the middle-level atmosphere was convectively unstable and obvious symmetric unstability,so the slantwise vorticity was developed,which led to the strong ascending movement and moist air upward transport and made the precipitation intensity increasing.The diagnosis analysis of ageostrophic wet Q-vector shows that the convergence of the ageostrophic wet Q-vector at 900hPa matches the heavy rainfall center corresponds well.The heavy rainfall center lied on the front of the movement of the ageostrophic wet Q-vector convergence center. On the other hand,the ageostrophic wet Q-vector had a forecast significance for the coming 12h rainfall area.