Analysis on Regional Torrential Rainstrom during a Consecutive Autumn Rain Event in Central and Southern Shaanxi

Based on the observation data,physical fields,and FY-2C satellite data,a regional torrential rainstorm process during an autumn consecutive rain event from 16 to 18 September 2011 was analyzed.The results show that the torrential rainstrom occurs under the circulation backgrounds of steady 'east high and west low' situations on 500 hPa.The blocking high over west Siberia and subtropical high are stronger.The persisting strong cold air from east and warm moist air from southwest provide a favorable background circulation for the development of torrential rainstrom.The jet streams on lower and upper levels are main effecting systems of rainstorm occurring.There is obvious difference between the stratification characteristics of rainstrom system and summer rainstorm,namely the rainstorm occurs under the steady stratification.The satellite image show that the cloud system of rainstorm is mainly to middle and lower clouds,the general minimum of TBB is-43 ℃.The contribution of easterly cold air on lower level is more than that on the middle level.Strong water vapor convergence of front zone on the lower level is the main effecting mechanism of the regional torrential rainstrom in autumn.