The Characteristics Of A Plateau Vortex Precipitation Event

Using various radar and disdrometer datasets from the third Tibetan Plateau Atmospheric Science Experiment,MODIS data,and the surface and sounding datasets at meteorological stations,this study analyzed the temporal and spatial variations,the synoptic-and meso-scale atmospheric circulations triggering rainfall,and the associated cloud-rainfall microphysical characteristics for one rainfall event on 14 July 2014 over Naqu in the central Tibetan Plateau,and theresults show that:?1?The results show that this rainfall process includes three stages,namely,one stage with heavy rainfall in the afternoon and two stages with weak rainfall at night.?2?Rainfall at the first stage is mainly produced by the development of a synopticscale plateau vortex and the formation of a meso-scale convergence line in front of the vortex circulation center.At this stage,the radar echo propagates northeastward.With the weakening of the plateau vortex,rainfall at the first stage ends.Rainfall at night is mainly associated with the warm and moist southeasterly flow passing over the topography near Naqu.The southeasterly flow provides favorable conditions of the atmospheric moisture,instability,and shallow dynamic elevation for the rainfall formation.With the intrusion of the low-level northeasterly flow,the radar echo generally propagates southeastward.?3?Moreover,at the earlier stage of the produced-vortex rainfall,the ascending motion is deep over the eastern vortex and exceeds 3 m s^-1 between 3 km and 11 km above the ground level,with the remarkable development of convections.At the later stage of the vortex-produced rainfall process,rainfall is mainly produced by stratiform clouds,with a higher cloud top.Rainfall at night is mainly caused by stratiform clouds with ascending motions in the upper layer of the cloud.The raindrop size distribution is wider in the afternoon?0.3-4.9 mm?than that at night?0.3-2.1 mm?.?4?For the plateau vortex which caused the first precipitation stage,the development of the low vortex was mainly caused by the strengthening of low-level convergence,while the upper vorticity advection and divergence terms strengthened the anticyclonic circulation.