Mesoscale Observational Analysis And Numerical Simulation Of A Heavy Rainfall Event In The Huaihe River Basin In July 2007

The heavy rain over the Huaihe River valley in July 2007 is one of the most serious rains in the history, in which there are two rainstorm stages over the place. The first stage occurred on July 4^th-5^th, and the second one took place on 8^th. The whole process continued about 10days during June 29 to July 10 and the first rainstorm was mainly analyzed in this article.The articles focus on the Mesoscale condition's impaction to the heavy rainstorm on center place from 22 o'clock of July 4 to 02 o'clock of July 5 and the district and the cause of the rainfall .By using FY-2C satellite data, Doppler radar data, Ncar/Ncep data, 10-minute data of intensive observational surface data and Automatic Weather Station data, the reasons of rainstorm and Maintenance mechanism in the Huaihe River basin during 4-5 July 2007 were analyzed. The development of mesoscale cloud cluster reflected spatial and temporal distribution of heavy rainstorm. Radar data shows the center place and the intension of heavy rain. By using surface encrypt data, the impact of humidity and temperature in the process of the rain was analyzed. Main results are as follows:1) large-scale weather situation: Huaihe Basin were controlled by South Asian high pressure, and situated in northerly gale on 200hPa; Subtropical high pressure 588dgpm line located in south of Yangtse Rive, and Huaihe basin was between 584dgpm line and 588dgpm line which provided favorable conditions for convergence of warm and wet air from south and dry air from north on 500hPa. Synchronously, water vapor channel provided rich water for the rain. All the factors provided good background for the rainstorms in Huaihe.2 ) Mesoscale condition: rainfall's occurring and developments were closely associated with the mesoscale system. The heavy rainfall took place in the heaviest mesoscale convection system. 3) When the water vapor was rich and instability condition happened, local mesescale ascending became the main trigger mechanism of heavy rain.By using WRF mesoscale model and NCEP reanalysis data from 20 o'clock 3^rd to 20 o'clock 5^th July, the heavy rain event was simulated. And vorticity, divergence and water-vapor flux divergence were calculated by using simulated datum.