Weather system classification and water vapor transport characteristics of extreme value rainstorm in northwestern Hunan

Abstract Using meteorological analysis, composite analysis and water vapor trajectory analysis, the extreme value rainstorm process in northwest Hunan was analyzed. The results show that three types are summarized: the Southwest Vortex and Warm Shear Line Pattern (SVWSLP), the Subtropical High Edge Pattern (SHEP) and the Cold Trough and Shear Line Pattern (CTSLP). The main influence systems are upper trough, southwest vortex, shear line, low-level jet and subtropical high edge. For SVWSLP, the water vapor transport channels are only from the low-latitude ocean whether it is affected by long-distance typhoons. For SHEP, the main water vapor channel comes from the long-distance ocean and is finally transported to northwestern Hunan around 650 hPa in the form of warm and wet airflow, whether it is affected by long-distance typhoons. The CTSLP appears a significant water vapor confrontation between the north and the south and the baroclinicity of the atmosphere in the rainstorm area. The southern and western boundaries are the input boundary, while the eastern and northern boundaries are the outflow boundary. Therefore, one of the three types of weather systems appears in northwestern Hunan in May–August, with strong water vapor transport from the ocean surface, which is likely to cause extreme rainstorm.