A study of convective clouds in the Tibetan Plateau based on dual polarimetric radar observations

Based on observations of a mobile C-band dual polarimetric radar (C-POL) and the Chinese new generation weather radar deployed in Naqu (CINRAD/CD) from 30 July to 5 August 2014, two hailstorm events and their associated dynamic, thermal-dynamic and microphysical characteristics are demonstrated using wind fields retrieved from observations of the two Doppler radars and identification technique of dual polarization radar hydrometeors. The convective cells mostly appeared in the afternoon in the Tibetan Plateau. Although the horizontal and vertical scales of the convective cells are small, they occurred frequently and evolved rapidly, and generally lasted for tens of minutes. In the RHI (range height indicator) images of Z_H, Z_DR and Class, the dynamic and microphysical processes can be seen clearly. Hydrometeor particles reached higher levels following the "0 line" and grew quickly, accompanied by increases in the echo intensity, and eventually formed a hail wall dropping down on the other side of main updraft. From the consecutive three RHI scans, it can be seen that the particles changed from wet snow to hailstorm during the evolutional process in one convective cell. The height of the echo was lower and its intensity was very weak when the convective cell was initially triggered. However, large amounts of wet snow appeared above the melting level, indicating that the updraft was strong enough to transport wet snow back to higher levels before the snow completely melted below the melting level. Through physical processes such as condensation, rime and attachment, the wet snow could rapidly grow into hailstones in just over 10 min. During the re-condensation of wet snow, the unstable structure further developed while the ascending and descending motions strengthened due to the latent heat release. Therefore, the occurrence of wet snow in a newly generated weak echo region above the melting level usually indicates strong updraft and convective cell would develop rapidly.