Comparative Analysis of Characteristics of Two Typical Rainstorm Cases in the East of Northwest China

The conventional surface and upper-air sounding meteorological data,the hourly precipitation data from AWS in Shaanxi Province and the NCEP 1°×1°reanalysis data were used to analyze two rainstorm processes respectively in 23—24 July 2010(0723) and 28—29 July 2011(0728).The results show that:the relatively stable circulation is the favorable background to the development of two major rainstorms,the low-level jet has established at early period of the 0723 precipitation.For the 0728 rainstorm,jet stream was from east to west at its early period;accompanied with the formation of low-level jet,the high-level jet stream enhances and turns upright,then heavy precipitation occurred.The southerly flow in the east of tropical depression Chanthu formed a wide and strong water vapor transport channel along the periphery of the subtropical high,however,the southeast airflow in the north of tropical storm Nock-ten merged with the southwest airflow from the Bay of Bengal and then transported to the rainstorm area during the 0728 rainstorm.Shaanxi Province is located in high-energy areas of θ_(sc) during the two rainstorm processes.There are invasions of the dry and cold air,and potential vorticity disturbance declines along the intensive areas of θ_(sc) in the two processes of rainstorm.Temporal changes in potential vorticity and precipitation almost take place simultaneously,and the appearance of large values of potential vorticity indicates the occurrence of rainstorm.