关键词: 暴雨, 降水特点, 环流特征, 气象要素, 前置特征

Abstract:

In order to strengthen the application of densified automatic station data in rainstorm forecast in the eastern Helan Mountain foothills, based on hourly surface meteorological observations and ERA5 reanalysis data, 17 rainstorm events in this area from 2016 to 2021 were classified into cold-warm air convergence type, warm-sector type, and weak cold air intrusion type, according to the intensity of cold air. The precipitation distribution, circulation characteristics, and the evolution of surface meteorological elements were then comparatively analyzed. The results show that cold-warm air convergence rainstorms are characterized by a deep upper-level trough and an extensive low-level high-humidity zone, but with relatively weak southerly winds and water vapor flux. These storms exhibit a wide precipitation area and high average rainfall, but the precipitation efficiency is lower than that of warm-sector rainstorms. Warm-sector rainstorms have the strongest low-level southerly winds and moisture flux, but the upper-level divergence is the weakest and the high-humidity zone is fragmented. These storms are marked by high precipitation efficiency, strong locality, and extreme intensity. In weak cold air intrusion rainstorms, the low-level warm and moist conditions are better than in the cold-warm air convergence type, and the precipitation and convective intensity which triggered by upper-level cold air are stronger than those of the cold-warm air convergence type. One hour before the onset of precipitation, all three types of rainstorms exhibit temperature drop, pressure rise, and increased wind speed, with temperature changes being the most significant, while dew point temperature varies between cases. In the five hours prior to precipitation, temperature decreased and relative humidity increased, with the most pronounced changes occurring one hour before rainfall onset. After precipitation began, these variables tended to stabilize. However, the timing and magnitude of temperature drops and the rate of relative humidity increase differed among the storm types. Dew point temperature first increased and then decreased, peaking from 1 hour before to 2 hours after rainfall onset. Wind speed variations also differed across storm types. The indicators developed in this study performed best for warm-sector type rainstorms, achieving a TS (threat score) of 48.65%, followed by the cold-warm air convergence type, with the weakest performance in the weak cold air intrusion type. The prediction accuracy of humidity, pressure, and dew point temperature indicators was relatively high (mostly exceeding 50.00%, some over 55.00%), indicating potential for enhancing rainstorm monitoring and early warning. In contrast, indicators based on temperature change (less than 50.00%) and wind speed variation (around 30.00%) showed weaker predictive capability, indicating the need for further optimization.

Key words: heavy rainstorm, the features of rainstorm, circulation traits, meteorological elements, preceding attributes