The Kinematic And Microphysical Characteristics Of The Convection In Meiyu Front Based On Polarimetric Radar Observations

The main precipitation system over eastern China in the summer is the Meiyu precipitation over the Yangtze-Huaihe river basin.In this region,the intense Meiyu precipitation is often accompanied by meteorological disasters,including severe flooding,inundations and mountain landslide.In recent years,the forecast of Meiyu front has been greatly improved,but the forecast of heavy precipitation associated with Meiyu front is still limited.Fully understanding of storm microphysics and its parameterization is important for improving the quantitative precipitation estimation and forecast.In this study,the kinematic and microphysical characteristics of a Meiyu precipitation system is examined by using the Nanjing University C-band polarimetric Doppler radar,the Dingyuan C-band polarmetric Doppler radar and the Hefei S-band Doppler radar observations during the 2014 OPACC field campaign.The maximum accumulated rainfall of this event was over 100 mm from 11 to 12 July 2014.We focus on the period which the Meiyu frontal stabilizes in observation area.The kinematic and microphysical characteristics of convective cells in Meiyu rainband are analyzed by polarimetric data and dual-Doppler analysis.Firstly,the precipitation zone along the Meiyu front is divided into north?stratiform?and south?convective?regions by 345 K pseudo-equivalent temperature contour.The characteristics of convective cells in two regions are compared.The convective rain zone containing isolated convection cells and linear convective systems consisted of many meso-y-scale convective elements appears to be an intense region.This region also contain some deep convective cells with 15 dBZ echo top height higher than 12 km.The stratiform rain zone is a broad,weak rainfall region with convective cells embedded in the stratiform.The convective contribution in south region is higher than 90%,while it less than 60%in the north region.Four hours maximum accumulated rainfall in the south region reaches 60 mm,while the maximum accumulated rainfall in north region is only 20 mm.In the south region,the convection is deep with the echo top of 30 dBZ higher than 10 km.The convection has a stronger updraft,the largest ascending velocity reaches 5 ms^-1,causing a stronger ice-phase process beyond the 0? level.Because of the strong ice-phase process,there are many different kinds and amounts of ice-phase particles above 0?level,especially hail and graupel.There are some large raindrops with differential reflectivity?ZDR?reached.3 dB?the median volume diameter D0?2.3 mm?caused by the strong collision-coalescence precipitation process.The south region possesses mainly high concentration of small raindrops,with ZDR of 0?2.0 dB.In contrast,the convective cells in the north region are more moderate,the 30 dBZ echo top height just reaches 8 km.The ice-phase process in the north region is weaker than it in south region,because of weaker updraft.Because the environment in the north region is dryer and the updraft is weaker,there are different microphysical characteristics between two regions.Due to the evaporation,there are less small raindrops.The raindrops in north region is smaller,focus on 0.2?1.5 dB,and the largest Do is just about 1.8 mm.The ice and liquid water content in the south region are much higher than them in the north region.Finally,because the convective cells in south region is more intense,the evolution of kinematic and microphysical characteristics of an isolated convective cell in the south region is analyzed.The stages in which we can observe is initiation,spliting,mature and dissipation four stages.The intense and echo top height of the isolated convective cell is enhanced from initiation to mature stage.The convective scale at the initiation stage is smallest,with 15 dBZ echo top reaching 10km possessing a small amount of large particles.With the growth of convection in the mature stage,the convective region and 15 dBZ echo top height are increasing,meanwhile the concentration of small-and median-raindrops is increasing.There are lager raindrops,with ZDR?3dB in these 3 stages.The convection reaches the strongest at the mature stage,with the maximum reflectivity?Z?of 58 dBZ and the 15 dBZ echo top height above 12 km,Also,the updraft at the mature stage is strongest,more than 5 ms-1?where?,and it causes a strong ice-phase,produce more hail and graupel,Because of a large concentration of small-and median-raindrops at the mature stage,the ice?? 5.0 gm-3?and liquid??8.0 gm-3?water are the highest at this stage.Then,the intensity and updraft of the convective cell begins to weaken,the maximum reflectivity?Z?is 46 dBZ with the 15 dBZ echo top height-10 km.There are no lager raindrops,the maximum ZDR is below 1.6 dB.Because of the dryer environment at this stage,smaller raindrops are evaporated.So,the raindrops is concentrated as the precipitation particle with medium particle size.