ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Analysis of the Causes and Raindrops Spectrum Characteristics of a Supercell Heavy Precipitation Event in Southern Shandong
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Abstract:
On the night of July 12, 2023, the vicinity of Feixian County, Shandong Province was affected by supercell heavy precipitation, resulting in a rare extreme rainstorm event. This paper comprehensively utilized multi-source observational data and ERA5 reanalysis data to deeply explore the circulation background of this extreme precipitation, the coupling mechanism of high and low-level jets, the activity characteristics of meso- and small-scale weather systems, and the microphysical characteristics of precipitation. The research shows that: (1) Favorable circulation patterns, environmental wind fields, and water vapor transport provided large-scale background conditions for the occurrence of short-term heavy precipitation. The thickness of the warm cloud layer and the maximum liquid water mixing ratio content were well correlated with the extreme heavy precipitation period. During the extreme heavy precipitation period, the warm cloud layer thickened rapidly, and the high-humidity area lasted for a long time. The enhanced cloud water content and the thickened saturated moist layer provided the prerequisite conditions for the formation of efficient precipitation. (2) The rapidly developing boundary layer jet (SW-BLJ) and the synoptic-scale low-level jet (SW-LLJ) overlapped and coupled vertically in southern Shandong Province, which promoted the extreme short-term heavy precipitation near Shangzhuang, Feixian County on the night of the 12th. The extreme rainfall intensity occurred in the left front side of the overlapping area of the double low-level jets from 21:00 to 22:00. (3) This precipitation process was affected by the synergistic action of multi-scale systems. The surface mesoscale convergence line triggered and promoted the occurrence and development of convective cells. The presence of a mesocyclone at the low level of the supercell strengthened the small-scale convergent upward motion, significantly increasing the precipitation. (4) This extreme short-term heavy precipitation had the characteristics of a mixed type of tropical oceanic and continental convective precipitation. At the beginning of precipitation, the raindrop spectrum changed significantly, manifested as a sharp increase in raindrop number concentration and a significant increase in raindrop diameter. Small and medium raindrops accounted for the majority, and the proportion of small particles with Dm < 2 mm was close to 85 %. The number of large raindrops increased with the increase in rainfall intensity. In terms of the contribution rate to precipitation, although medium particles with a diameter of 2 - 3 mm only accounted for 11.77 %, they contributed the most to precipitation. Followed by small particles with a diameter of 1 - 2 mm. Although the proportion of larger particles with a diameter of 3 - 4 mm was small, accounting for 2.947 %, their contribution also accounted for 23.108 %. Although the number of small particles with Dm < 1 mm was large, accounting for 43.354 %, their contribution was less than 4 %.
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