Abstract:Using the observational data provided by MICAPS, the characteristics of the moist potential vorticity of two abrupt torrential rain events in Guanzho ng, Shaanxi on June 29, 2004, and in northern Shaanxi on August 10, 2004 are ana lyzed. The results show that at 700 hPa level, the generation of a mesoscale c onvective instable area with MPV1≤-0.3 PVU and a mesoscale convective stab le area with MP1≥0.3 PVU at the upper stream, is favorable for moist barotropi c features, and contributes to the occurrence of abrupt torrential rains. The favorabl e moist baroclinic features develop at 700hPa level, while the plateau trough mo ves eastwardsto Hetao area or Guanzhong area. A moist baroclinic center with MPV 2＜0 generates at the rear of the trough, as a moist baroclinic center with t he MP2＞0 is in front of the trough. The positive and negative moist barocl inic centers above rainfall location and its neighboring upper stream, form an isoline concentrated zone of MPV2, which coupled with the mesoscale convective i nstable center with MPV1≤-0.3 PVU accords to the rainfall location. On MPV 1 zonal crosssection chart, an MPV column, nearly through upper and low levels, builds up in westtilting with height at neighboring upper stream of the rainfall location before the Guanzhong torrential rain. While at Ansai, a funnellike positive MPV extends from upper level down to the lower troposphere, which overlaps the nega tive MPV area developing in the boundary layer. The deep negative MPV la yer develops above the rainfall location. Simultaneously, at the midlow level of tropo sphere, the positive MPV column moves eastwards to the rainfall location to f orm a steep isolineconcentrated zone of MPV, which holds indicative meaning to theoccurrence of abrupt torrential rains. The MPV disturbance owns the characte ristic of spreading from high to low latitudes. Its threedimensional structure and evolution are the useful information in predicting abrupt torrential rain occurr ing in the eastern Tibetan Plateau.
