A Case Study on the Rainstorm-Producing Mesoscale Vortices in Central-Eastern China

During 26-27 June 2022, mainly influenced by three mesoscale vortices, central-eastern China (particularly for Henan and Shandong) experiences the first widespread torrential rainfall event of the 2022 flood season (maximum 24-hr accumulated precipitation is similar to 380.9 mm), resulting in severe social impacts. The three mesoscale vortices form and sustain under favorable background conditions, mainly including a strong upper-level divergence, an intense middle-level warm advection, and a powerful lower-level convergence associated with a low-level jet. Among the vortices, the vortex which forms over Shandong, lasts for similar to 9 hr, and makes a much larger contribution than the other vortices to the accumulated precipitation, is defined as the primary vortex. More than a half of the hourly precipitation peaks in this event appear in the life span of the primary vortex, which is closely related to the variations of the vortex in its cyclonic-vorticity and vertical extent. Backward trajectory analysis indicates that air particles originating from the lower troposphere southwest of the primary vortex contribute the most to its formation (similar to 82.7%). These air particles mainly experience a notable increase in their cyclonic-vorticity due to convergence-related vertical stretching, which directly renders the formation of primary vortex. During the whole life span of the primary vortex, convergence-related vertical stretching is the most favorable factor for its development/sustainment, and the convection-related vertical transport of cyclonic vorticity ranks second; whereas, the horizontal transport is the most detrimental factor. Moisture budget shows that Southeast China is the most important moisture source for this event (accounting for similar to 48.9%). Due to global warming, extreme weather and climate events occur with a higher frequency and a stronger intensity in China. Of these, a widespread heavy rainfall occurs in central-eastern China during 26-27 June 2022, which causes severe impacts on society. Our attention is drawn to understand how the extreme rainstorm forms and where the main moisture sources are located. For this, we analyze this event by using automatic station data and reanalysis data and discover that three mesoscale vortices are the primary reason for the heavy rainfall. Among the vortices, the one with the longest life span contributes the most to the accumulated precipitation. The strong convergence in the lower troposphere dominates the formation/maintenance of the vortex. Southeast China continuously supplies moisture for the rainfall (similar to 48.9% in contribution). This research is helpful to enhance the understanding of this type of heavy rainfall event. Affected by three mesoscale vortices, central-eastern China experiences torrential rainfall, with a rainfall peak of similar to 380.9 mm observed The primary vortex, which is produced by vertical stretching, is directly related to more than a half of the hourly rainfall peaks Southeast China provides similar to 48.9% of the moisture for the rainfall, which is mainly transported by the Southwesterly/southerly wind