A comparative study on the formation mechanisms of "11.6" persistent and "13.4" short-term extreme heavy precipitation events in South China

Based on ERA5 reanalysis data and hourly gridded precipitation dataset produced by merging China’s automatic weather-station observations with the NOAA(National Oceanic and Atmospheric Administration) Climate Prediction Center’s CMORPH (Climate Prediction Center Morphing Technique) satellite-derived precipitation estimates, this study comparatively analyzes the formation and development mechanisms of the persistent extreme heavy precipitation event on June 29th, 2011 (hereinafter called "11.6" event) and the short-term extreme heavy precipitation on April 25th, 2013 (hereinafter called "13.4" event) along the coastal region of South China. From perspectives including synoptic circulation patterns, moisture transport, and vorticity budget, the results show that the "11.6" event was associated with a stable low-pressure weather system, dominated by an upper-level vortex that provided dynamic lifting and sustained by a steady low-level moisture transport band. In contrast, the "13.4" event lacked a stable synoptic system and exhibited weaker low-level moisture transport. However, it produced intense hourly rainfall due to transient but strong low-level moisture convergence. The "11.6" event featured greater positive vorticity advection, and the low-level jet was crucial for vorticity input in the lower troposphere, while the generation and intensification of mid-level vortices were key to vorticity input in the mid-troposphere. Furthermore, the positive feedback between these two processes played a vital role in sustaining the heavy precipitation.