Numerical Simulation Analysis On Conventional Data Assimilation For A Rainstorm In Chongqing

Base on synoptic analysis on the heavy rainfall process which occurred in Chongqing region from 31^st August to 2^nd September with multiple observational data,numerical simulation experiments were conducted with WRF model adopting WRF 3D-Var assimilation system assimilated conventional sounding data into the initial field,and comparing analysis on the spatial distribution of precipitation,the structure of mesoscale system and cloud microphysical process as well as entrainment with and without assimilated conventional sounding data.Finally,diagnose analysis of moist potential vorticity?MPV?were conducted by high resolution at spatial and temporal output with assimilated conventional sounding data.The mainly results as following:1)Synoptic analyses indicate that the rainstorm has closely relationship with the development of southwest vortex,shear line and LLJ at lower level of troposphere,and westward movement of subtropical high as well as the South Asia High associated with upper jet at 200 hPa;the interaction between?and?mesoscale convective cloud clusters and development of low vertex shear line is the main causing of the heavy rainfall.2)Comparing of simulated results with and without assimilated conventional sounding data with WRF model show two experiments could reproduce the large-scale circulation features and mesoscale system during the evolution of the rainstorm,and the simulated precipitation was improved at spatial distribution and intensity when conventional sounding data was assimilated into the initial field,the improvement is significant on rainfall intensity above rainstorm level.3)Comparing results show that the large-scale systems?the South Asia High and subtropical High?and mesoscale systems?low vortex and LLJ?as well as moisture transport which closely related to the occurrence of the heavy rainfall were all strengthened after assimilated conventional sounding data,these can provide more favorable conditions for the development and maintenance for MCS.The stronger convergence at low level and divergence at high level associated with obvious vertical movement et al appeared around the simulated MCS,the maximum convergence of moisture flux divergence is located at 700 hPa above the center of precipitation,however it is not the location of maximum moisture flux.Simulated physical field are enhanced in some degrees such as divergence,vorticity,moisture flux and its divergence as well as vertical velocity et al,which are one reason of better simulated results by assimilating conventional sounding data into the initial field.4)Comparing of cloud microphysical process and FMSE by with and without assimilated conventional sounding data into the initial field of WRF model show that simulate results with assimilation weakens the negative influence of entrainment for the precipitation effectively,which means,assimilating conventional sounding data can not only improve the quality of large scale field,but also affect the formation of rainfall in cloud microphysical.5)Diagnosis of MPV indicate that the“positive and negative”vertical distribution of MPV1favored the occurrence of rainfall,the precipitation mainly appeared in the positive and negative transitional zones of MPV1 which represent the converging of cold and warm air.Vertical distribution of MPV2 shows the convective instability and conditional symmetry instability may be the triggering mechanisms of rainstorm,the abnormal increase of MPV's extremum is related to the occurrence of precipitation,conditional symmetry instability plays a major role in the first two stages of precipitation and convective instability play a major role in the third stage.