ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Study on the Formation Mechanism of a Backward-Propagating Heavy Rainstorm Event Based on Multi-Source Observation Data
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Abstract:
On August 4, 2024, a heavy rainstorm (referred to as the “24·8” extreme rainfall event) occurred at Wucheng Station in Dezhou, Shandong Province, breaking the historical records for both daily precipitation and maximum hourly precipitation at the station. This study utilizes intensive automatic weather station observations, Doppler weather radar, wind profiler radar data ，and ERA5 reanalysis and GDAS data, combined with the HYSPLIT model, to reveal the multi-scale physical mechanisms that enabled the long-lasting back-propagating convective system and its associated extreme rainfall. The results indicate that this event occurred under a large-scale circulation pattern characterized by a rearward-tilted trough confronting the subtropical high. Low level jet (LLJ) and super low level jet (SLLJ) persistently transported abundant moisture from the South China Sea and the Bay of Bengal to northwestern Shandong, establishing an extremely unstable environment with high energy, high temperature, and high humidity within the warm sector ahead of a surface front. The cold pool outflow generated by precipitation interacted with the ambient warm, moist airflow, forming a quasi-stationary convergence line. Coupled with temporal and spatial pulsations of the LLJ, this interaction continuously drove new convective cells to propagate southwestward, directly causing the extreme heavy rainfall. Dynamic energy reconstruction was key to the system''s maintenance: although rainfall consumed unstable energy, persistent warm, moist advection transported by SLLJ allowed convective available potential energy to be rapidly rebuilt and maintained near its peak. This process established a positive feedback self-sustaining mechanism characterized by energy reconstruction leading to the sustained occurrence of the back-propagating heavy rainfall.
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