Numerical Simulation And Diagnostic Analysis Of A Rainstorm In Yangtze-huaihe River Basin Based On Radar Data Assimilation

Systems with the response under climate are changing constantly.In recent years,the observation data have become more refined and the model accuracy has been improved.After improving the effect of conventional numerical simulation based on radar data assimilation,the different characteristics of the numerical simulation and diagnostic analysis of the rainstorm in Yangtze-Huaihe river basin in the past two years may be explored.Threedimensional variational(3DVAR)assimilation and numerical simulation were carried out for the rainstorm process in Yangtze-Huaihe river basin on July 5,2018.The experiment used GFS(Global Forecast System)data of NCEP and C-band dual-polarization radar data of Nanjing University of Information Science & Technology,and used WRF(Weather Research and Forecast)mesoscale model and its WRFDA assimilation system.Before the data assimilation test,the "matching identification method" is used to reduce the effects of ground clutters and shield clutters.The anti-noise Dealiasing Algorithm(AND)is used for velocity dealiasing.The different scaling factors in the assimilation test were set up in order to improve the experimental effect and make the radar data absorbed better in the model.Compared with the simple numerical simulation test in general,the numerical simulation test based on the radial velocity and reflectivity factors of 3DVAR NUIST RADAR assimilation can better simulate the location and development process of the precipitation,intensity and mesoscale convection system(MCS).It can also better describe the occurrence and development of the rainstorm and MCSs in Yangtze-Huaihe river basin.Output data from the numerical simulation of the 3DVAR radar data assimilation were applied to analyse the mechanism of the rainstorm process.The squall line system in the north of Jiangsu and a MCS in the southwest of Jiangsu were the trigger systems for the short-term heavy rainfall.High and low air jet coupling,low level convergence and high level divergence.Meanwhile the strong upward movement to the tropopause generated by the positive vortex tube of the whole layer,provided favorable dynamic conditions for the occurrence and development of heavy precipitation and squall line system in the rainfall area.Significant wet area,southwest water vapor transport and convergence,potential instability and high energy region together provided moisture and heat conditions.The analysis of the moist potential vorticity(MPV)shows the particularity of this rainstorm.One is the unstable energy had a lower position.In addition,both barotropic part(MPV1)and baroclinic part of moist potential vorticity(MPV2)were stuck in the middle of low value regions on the east and west sides,which was the reason why the rainstorm developed violently and maintained a short time.