The Effect of Plateau Vortex Shear on the Heavy Precipitation Distribution and Water Vapor Characteristics in Yunnan

Using observational data and NCEP/NCAR reanalysis data, the characteristics of plateau vortex shear during the summer of 2008–2012 are analyzed. This phenomenon moves southeastward to Yunnan Province, resulting in heavy precipitation. The results show that these events are mainly divided into three types: The strong cold air behind plateau vortex shear, supplementation of plateau vortex shear, and weakening of the southeastward plateau vortex shear. Among them, the third type has the highest frequency in Yunnan. Northern–central Yunnan is the main area receiving heavy rainfall and is typically affected area of plateau vortex shear in Yunnan, with rainfall mainly occurring at night. The first type of event has the largest influence area, which can cause rainstorms throughout the province but is less frequent. During the second and third types of events, a high is maintained (ridge) between Yunnan Province and Myanmar. Precipitation area and water vapor transportation are influenced by subtropical high location, vortex shear meridionality, and the time. There is an obvious income of water vapor in Yunnan during these heavy rainfall events; the meridional moisture income is stronger than the zonal moisture output. Using the HYSPLIT model, water vapor transportation by rainstorms is analyzed. The Bay of Bengal is the most important water vapor source. In northern Yunnan, water vapor contributions from the Tibetan Plateau are important. Some moisture over the Tibetan Plateau comes from the region near the Arabian Sea, while other portions originate from the Bay of Bengal. Throughout this transportation, each air flow may experience several cycles of evaporation and precipitation influenced by the terrain.