The Observed And Simulated Study For The Microphysical Characteristics Of The Meso-scale Convective Systems With Intense Rainfall In Eastern China

The climate in eastern China is deeply influenced by the east Asian monsoon,flash floods associated with several kinds of meso-scale convetive systems with intense rainfall occur frequently during the summer time,causing severe damage to properties and loss of lives.To improve the performance of quantitative precipitation estimation(QPE)and forecast(QPF),it's essential to understand the microphysical characteristics of these systems.Based on the observation datasets from polarimetric radar and other instruments during the 2014 Observation,Prediction and Analysis of Severe Convection of China(OPACC)field campaign,this study focus on the understanding of microphysical structures and surface drop size distributions(DSD)among several precipitation events belonging to different types of convection systems(meiyu rainband,outer rainband of landing typhoon and squall line systems).Based on the analysis of the microphysical characteristics,the performances of radar QPE for these rainfall cases are improved using a composite rainfall estimator.On the other hand,a typical summertime intense precipitation event is simulated using different microphysics schemes and the microphysical features are evaluated with polarimetric radar observations.Error sources of simulated microphysical characteristics are diagnosed and discussed as well.Firstly,based on the combined observations of polarimetric radar and disdrometer,the precipitation structures and DSD characteristics of three meso-scale convective events with intense rainfall in eastern China are compared.It shows that these intense rainfall convections initiated in this midlatitude region of eastern Asia frequently represent the typical DSD characteristics of warm-rain convecti ve type in low latitudes,though the ice-based convective DSD features can also be shown but with lower frequency.Co-exist of the two types of DSDs somewhat suggesting the unique microphysical characteristics in eastern China.And the surface DSDs with intense rainfall are mainly shown the combination of high raindrop concentration and medium raindrops,indicating the microphysical features of heavy precipitation here.According to the observations of vertical microphysical processes and environment conditions,all there summertime precipitation events are with equally deep warm cloud layers,warm-rain processes are always essential in determining the surface DSDs.Convections of the meiyu and typhoon rainband are initiated in the relatively moist and stable environment,ice-phase processes are suppressed but warm-rain processes like coalescence are active.While for the squall line case in drier and more unstable environment,convections develop much deeper and ice-phase processes are more active.The melting of the large ice particles leads to large raindrops at upper warm cloud layer,the evaporation and even size-sorting processes can cause low number concentration and high mean size of raindrops at surface in certain periods.Secondly,polarimetric radar rain estimation is studied and improved based on the understanding of microphysical characteristics from these precipitation systems.Several rainfall estimators are derived using the statistical disdrometer datasets in eastern China.And their QPE performances are evaluated in the chosen there convective events with intense rainfall.It shows that for certain rainfall estimator,the accuracy of QPEs is affected by the variation of DSDs in different rain regimes.The trade-offs among different rainfall estimators suggest the potential benefit of using a new composite rainfall estimator.And the composite QPE estimator is also proven to outperform any single rainfall estimator.Finally,based on the observed analysis of the microphysical features from these meso-scale intense rainfall convective systems,a typical meiyu rainband case is selected and simulated using the Weather Research and Forecast(WRF)model.Three widely used two-moment bulk microphysics schemes are chosen for the simulation and their forecast microphysical characteristics are evaluated compared with radar observations.Overall,the observed features are well placed in the three forecasts,while the intensity and microphysical structure of the simulated precipitation differ from the polarimetric radar observations.Contents of snow or graupel are higher than observations above the freezing layer,and the melting of these unreal ice particles could disturb the warm-rain processes at lower levels.On the other hand,the high efficiency of collision-coalescence is not shown at the warm cloud layer in the forecasts as in the observations,causing the unreasonable DSD characteristics at surface.The scheme presented the best simulated microphysical feature is selected for the further diagnosis of specific microphysical processes.Limitations of certain microphysical processes are investigated and help for the modification of the key parameters.