Abstract:On the night of 12 July 2023, a rarely-seen extreme torrential rain event occurred near Feixian County in Shandong Province, under the influence of a severe precipitation supercell. This study comprehensively uses multi-source observational data and ERA5 reanalysis data in investigating the circulation background, coupling mechanism of upper- and lower-level jets, characteristics of meso- and small-scale weather systems, and microphysical features of precipitation associated with this extreme event. The results show that this event was driven by the synergistic effect of multi-scale systems. Favorable circulation patterns, ambient wind fields, and water vapor transport provided large-scale background conditions for the short-time heavy rainfall. The rapidly developing southwest boundary layer jet (SW-BLJ) coupled with the synoptic-scale southwest low-level jet (SW-LLJ) over southern Shandong enhanced upward motion in the middle and lower troposphere. Meanwhile, convergence in the middle and lower troposphere, combined with upper-level divergence in the northeastern divergent zone of the South Asian high, further strengthened deep-layer upward motion. Under the combined influence of the double low-level jets, mesoscale convective systems developed intensely in southern Shandong, promoting the occurrence of heavy rainfall. Furthermore, the event exhibited mixed characteristics of both tropical maritime and continental convective types. At the initial stage of precipitation, there was a sharp increase in raindrop number concentration and a significant enlargement of raindrop diameters. During the peak rainfall period, small particles with a mass-weighted mean diameter (Dm)<2 mm accounted for nearly 85.00%, and the number of large raindrops increased with the intensification of rainfall intensity. In terms of contribution to precipitation, although medium-sized particles (2-3 mm) only accounted for 11.77%, they contributed most to precipitation, reaching 32.74%, followed by small particles (1-2 mm). Although particles with Dm<1 mm were the most numerous, accounting for 43.35%, their contribution to precipitation was less than 4.00%. The severe precipitation supercell stage showed an “upscaling” feature. Particles in the 3-4 mm range, although accounting for less than 6.00% in terms of frequency, contributed 30.04% of the total precipitation, while particles with Dm>6 mm contributed 8.81% to the precipitation.