关键词: 短时强降水, 环流分型, 主成分分析, 物理量差异, 概率密度

Abstract:

The synoptic classification of short-duration heavy rainfall (SDHR) circulation patterns is of great significance for improving forecasting and early warning capabilities, as well as enhancing meteorological disaster prevention and mitigation. Based on hourly precipitation data from May to September during 2005-2022 and ERA5 reanalysis data, this study employs the obliquely rotated T-mode principal component analysis to investigate the circulation patterns, precipitation characteristics, and environmental parameter differences associated with SDHR events in the Shaying River Basin. The results indicate that SDHR events during the warm season can be categorized into five circulation types: the pre-trough southwesterly flow pattern, the southwesterly flow pattern on the periphery of the subtropical high (STH), the northwesterly flow pattern, the low vortex shear pattern, and the typhoon low pressure pattern. Among them, the pre-trough southwesterly flow pattern occurs most frequently, while the typhoon low pressure pattern is the least. In terms of precipitation intensity, the pre-trough southwesterly flow pattern shows a relatively uniform distribution; the southwesterly flow pattern on the periphery of the STH exhibits strong local characteristics; the northwesterly flow pattern produces stronger precipitation in the southwest; the low vortex shear pattern features higher intensity in the northern and central parts; and the typhoon low pressure pattern shows maxima mainly in the western and northern high-altitude areas. Regarding precipitation probability, the low vortex shear pattern exhibits higher probabilities in mountainous areas and northern regions, whereas the other four types display opposite spatial tendencies. On the monthly scale, the pre-trough southwesterly flow pattern dominates in May, the northwesterly flow pattern prevails in June, both the pre-trough southwesterly flow pattern and low vortex shear pattern are dominant in July, the northwesterly flow pattern becomes most prominent in August, and both the southwesterly flow pattern on the periphery of the STH and pre-trough southwesterly flow pattern are predominant in September. The diurnal variations reveal that the pre-trough southwesterly flow pattern, the southwesterly flow pattern on the periphery of the STH, and the low vortex shear pattern exhibit bimodal structures with differences in peak frequency and duration; the northwesterly flow pattern shows a single afternoon peak, while the typhoon low pressure pattern has no obvious diurnal variation. Analysis of individual physical parameter indicates that the southwesterly flow pattern on the periphery of the STH and the typhoon low pressure pattern are characterized by abundant water vapor; both the southwesterly flow pattern on the periphery of the STH and the northwesterly flow pattern feature significant thermal instability, manifested as high convective available potential energy (CAPE) and a large 850-500 hPa temperature difference; the low vortex shear pattern and the typhoon low pressure pattern exhibit strong low-level convergence and upward motion; and all five circulation types are associated with weak vertical wind shear. Joint probability density analysis of environmental parameters further reveals that different SDHR types tend to develop under distinct combinations of thermodynamic and dynamic conditions, corresponding to different precipitation formation mechanisms.

Key words: short-duration heavy precipitation, circulation classification, principal component analysis, physical quantity differences, probability density