| Based on the high resolution observational data from July to August,2014 in Naqu,Tibet,detected with the mobile C-band dual polarimetric radar(C-POL).Take two rapidly growing,hail-producing storms observed on 30 July and 5 August 2014 as examples,the kinematic characteristics of convection clouds are analyzed by means of two Doppler radars wind field retrieval which are formed with dual polarimetric radar(C-POL)and Naqu new generation weather radar(CINRAD\CD),the class changes of convection clouds are analyzed by means of dual polarization radar hydrometeor class identification technique.The dynamical,microphysical and thermal characteristics of hailstorm cells over Tibet plateau are detailedly demonstrated.The conclusions are as follows:The convective cells in two cases appear in the aftemoon(BJT).From the wind field retrieval area,multiple cells develop at the same time,they are frequent occurrence and rapid evolution,these cells weaken quickly,clouds are not deep enough,hails are smaller in diameter which are mostly graupels,which generally last for dozens of minutes.The intensity of convective clouds increases rapidly which reaches about 60 dBZ,while the horizontal and vertical scales of cells are small.The horizontal scale of the strong echo region(>45dBZ)is not more than 8km and the vertical scale is not more than 4km.Because of the high terrain,convective clouds in summer in the plateau generally appear above 0? level.In the RHI(range height indicator)images of ZH,ZDR and Class,the whole dynamic and microphysical process can be obviously seen in where the hydrometeor particles raise and grow up following the "zero line" and accompanying the echo intensity increase,then form a hail wall dropping down in the other side of main updraft after overtaking it.From the successive three RHI scans,the class of particles change from wet snow to hailstorm during the evolution process in one convective cell.The height of the echo is lower and its intensity is very weak when the cell is just triggered.However,when a large amount of wet snows appear above the melting level,it always hints that the updraft is so strong that the wet snows are brought back to high levels while they have not completely melted in the air below the melting level.However,the wet snows have not yet been condensed into dry snow.During the recondensation of wet snows,the latent heat releasing will promote the unstable structures and further strengthen the updraft,and the cell will develop further.Through physical processes such as condensation,rime,and attachment,the wet snow can rapidly grow into hailstones in just over 10 minutes.Therefore,if numerous wet snows appear in a newly generated weak echo region above the melting level,it usually indicates that the region occurs strong updraft and will develop rapidly to a strong cell.The configuration of wind field in different height levels obtained by 3D wind field retrieval shows that the existence of wind shear accelerates the updraft.This is conducive to the conversion of unstable energy to kinetic energy,and cells can develop rapidly.Combined with the wind field and class,it can be seen that updraft region often corresponds to wet snow and the downdraft region often corresponds to dry snow and graupel,... |
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