Precipitation Structure And Echo Evolution Analysis Of Heavy Rainfall Caused By Departure Plateau Vortexes

After moving off the Tibetan Plateau eastward, the plateau vortex often leads toheavy rainfall in downstream areas such as Sichuan Basin, the northern China, eventhe southeast China. This thesis uses a variety of observational data, especially thenew generation Doppler weather radar mosaic data, studies the precipitation structuresand echo evolution of the heavy rainfall, from the relation between the plateau vortexand its corresponding precipitation systems. First, TRMM PR data is used to testifythe validity of ground based radar mosaic data. After examination, mosaic is fewaffected by topography within the range of the two cases occurred andthree-dimensional mosaic echo reflectivity is well continuous and reliable. Then, twoheavy rainfall cases occurred in the Sichuan Basin and the North China Plain areselected to analyze weather and precipitation structure. Occurred in30-31July2009,in the leeward of Tibetan Plateau, precipitation appeared in the environment ofsouthwest vortex and vortex interacting. The precipitation system is located in thesoutheast plateau vortex side, with the decline of the vortex moving out of the basinplateau and eventually dissipated. The intensity of precipitation system is lagged withthe vortex’s, while the speeds of the two are more consistent. In the condition ofcomplex terrain, clouds after dropping into the basin below the freezing height wouldmelt into a liquid layer, making the clouds from convective precipitation type intostrait-form type and showing a two-layer structure. On17-19July2010, there was aheavy rainfall case in the eastern China caused by the departure plateau vortex. Thisvortex plateau moved eastward in a typical saddle Circulation and was guided by theEast Asian trough. At the beginning, when the plateau vortex appeared, thecorresponding precipitation systems were not developed rapidly. There was also a6-hour lag between the vortex and precipitation. Besides, precipitation echo waslocated on the right side of the moving direction of the vortex, namely the southeast.When the cut-off low pressure developed to decay, the precipitation showed a similarecho tropical cyclone spiral cloud band structure. Precipitation with the plateau vortexdeveloped into the sea before the period to keep the local development. When thevortex started toward the Bohai and declined, precipitation echo dissipated rapidly.