Diagnostic Analysis And Numerical Simulation Of A Rainstorm Process In Nanjing

In this work,to analyze the rainstorm weather process in Nanjing July 5th,2018,methods such as moist potential vorticity,moist Q vector,convective effective potential energy and storm relative helicity,NCEP(National Centers Environmental Prediction)global objective analysis data,Micaps routine data,Chinese automatic station and CMORPH precipitation product fusion The hourly precipitation grid data set and related content in the WRF(The Weather Research and Forecasting)numerical model has been applied.After research,following conclusions are drawn.(1)Heavy rainfall areas appear in these places,such a right side of the entrance area of the upper jet and the left front of the center of the maximum wind speed of the lower jet.The northeast dry cold air from the south side of the North China high pressure and the warm and humid air from the Bay of Bengal are very active,forming a shear line in the Jianghuai region,providing a favorable dynamic mechanism for heavy rains.Abundant water vapor,accumulation of unstable energy with high temperature and high humidity,and strong vertical ascent movement are the main reasons for the maintenance and development of rainstorms.(2)The simulation results just meet the actual situation in the rainstorm area,the precipitation and precipitation time.The 1h forecast field output by the WRF numerical model can more intuitively reflect the weather process of this Nanjing rainstorm.The mesoscale low vortex on the Jianghuai shear line is stable and less moving,providing a dynamic mechanism for the rainstorm.The convergence of the ground wind field is the key trigger mechanism of this heavy rain process.The low-level convergence strengthens the vertical ascent movement and makes the convection develop vigorously,and then the heavy rain is formed.(3)The water vapor during precipitation mainly comes from the Bay of Bengal.It is transported to the Jianghuai region through the southwest of China.The mid-scale large wind speed center along the low-level jets forms a wind speed convergence above Nanjing,which strengthens the horizontal transport of low-level water vapor and provides important rainstorms.Water vapor conditions.The rainstorm falling area often appears in the area where the water vapor flux divergence is large and where the gradient is maximum.(4)Before the rainstorm occurred,a lot of unstable energy was accumulated over Nanjing,and the massive release of unstable energy provided important thermal conditions for the occurrence and development of the rainstorm.MPV1<0,MPV2>0 in the lower layer when the rainstorm occurred.(5)The convergence of the ageotropic Q-vector convergence zone is better than the quasi-geotropic Q-vector in forecasting the precipitation area in the next 6 hours.When combined with Q vector divergence,the prediction effect is better.The change of the value of the frontogenesis function is indicative of the rain intensity,but the positive value center of the frontogenesis function has a poor indication of the rain falling area.The difference of the frontogenesis function with mesoscale characteristics is used to express the change of the frontogenesis function,which has a better effect for diagnosing the falling area of precipitation.