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 θse during the two rainstorm processes. There are invasions of the dry and cold air, and potential vorticity disturbance declines along the intensive areas of θse 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.