The Diagnose Analysis And Numerical Simulation Of Jiang Huai Shear Lines With Heavy Rain During Meiyu

In June and July every year, intense fall always is centralized in Jiang-huai river drainage area, which causes severe floods in high frequency. This stage is called Meiyu-flood-season. Jiangsu located in middle and lower reaches Yangtze River, as an important base of industrial and agricultural production in China, cause heavy economic losses and casualties, once the flood and waterlogging calamity apprears. It is important to redouble our efforts in reaseach of mechanism on torrential rain, and in improving on measuring and forecast capacity. The paper concentrates on the study of shear line heavy rain on general circulation and the principal impacting systems, pysical mechanism, mesoscale system, the change of water vapor in the south of shear line working in intensity and location of rainstorm, exporing composit and comparative analysis, diagnostic analysis, numerical simulation. We can summarize the key components of the paper as follows:1. We haved yielded new insights, through researching in characteristics of general circulation in shear lines with heavy rain and without heavy rain, uing composit and comparative analysis. The two kinds of precipitation have shear line and vortex in low-level wind, which cause wind direction convergence. But reinforcement of meridional wind leads to shear line development and wind direction convergence to be strengthened in shear line with heavy rain. In the south of shear line, enhancement of southwest wind jet stream causes wind speed convergence. West wind at200hPa increase to jet stream and the center of jet stream lies in the ocean. Convergence in the low-level and divergence in the upper level is coupling. In shear line without heavy rain, thouth shear line and vortex appear in low-level wind, the configuration isn’t beneficial to further development of shear line and vortex. Meridional wind doesn’t increase obviously, so the shear line doesn’t enhance. Without southwest jet, wind speed convergence is week. At200hPa, the center of jet is so far away from Jiangsu that the divergence of high level isn’t powerful.2. We have obtained new results, by studying on dynamic, thermal feature and difference in shear lines with heavy rain and without heavy rain with composit and comparative analysis. In shear lines with heavy rain and without heavy rain, cyclonic vorticity bands are corresponding to shear lines. They have a period of warming and humidification. However, configuration of dynamic, thermal condition and water vapor transport are different from each other. At the same time, different intensity of dynamic and thermal condition, correspond to different intensity precipitation in shear line with heavy rain.3. Mesoscale analysis of the shear line torrential rain along Yangtze River basin in Jiangsu province is performed, which has uncovered some new facts. Low-level jet, shear line and vortex at700hPa (850hPa), southwest air flow of the border of subtropical high at500hPa and Meiyu front on surface work in with each other, which is favorable to guide mesoscale systems moving throuth Jiangsu persistently. The results show that the heavy rainfall has the feature of obvious mesoscale. An increase activity of ten rain clusters directly brings about the torrential rain. Humid tropical instable area in south of shear line provides dynamic and thermal energy for development of rain clusters. The surface mesoscale convergence system may trigger rain clusters. Cloud clusters take on southeast-northeast. Cloud clusters regenerate and develop backside continuously. The distribution of cloud is in keep with shear line. Three β-MCS turn up in Jiangsu one after another during the course of rainstorm. Pulsating and expandingly descending of low-level jet index is always in close contact with heavy rainfall.Augmentation of index is prior to reinforcement of rainfall. The process of heavy rainfall appears adverse wind area.4. The sensitivity tests about thickness, strength and distribution of water vapor in south of shear line are studyed by using WRF model, which have obtained significant results. Different thickness of water vapor may cause strength and distribution of precipitation change. When water vapor reduced in high of troposphere, precipitation intensity decreased a litter bit and the distribution of rainband was close to controlled test’. When water vapor reduced in high and middle of troposphere, the intensity and location of precipitation core hadn’t changed much, but the intensity and distribution of rainband had changed obviously. When water vapor reduced in lower, middle and high of troposphere, the intensity of precipitation core had sinked rapidly and its location had deviated from controlled test’evidently. The intensity and distribution of rainband had changed completely. With thickness increasement of water vapor, the intensity, location of precipitation core and distribution of rainband came close to controlled test’. As strength enhancement of water vapor, the intensity of precipitation core had heightened, and the extent of rainband had expanded. Water vapor in south of shear line slid southward, had great effects on the intensity, location of precipitation core and the whole rainband. The alteration of water vapor in south of shear line may cause the intensity of shear line and distribution of southwest jet change. At the same time, it also may have an influence on MPV and divergence in high and low level.