Abstract:

In this study, we selected a total of 27 short-time heavy precipitation events in Pingliang, Gansu province from June to August in the years of 2015-2019.Based on the hourly precipitation data obtained from automatic stations and upper-air sounding data, we analyzed the spatiotemporal distribution of these short-time heavy precipitation events, the influencing weather systems, and the background atmospheric environment using the methods of threshold classification and statistics, and conventional weather analysis.The results indicated that short-time heavy precipitation events occur less in June and mostly occur in the Liupanshan areas.In July, short-time heavy precipitation events occur more frequently and concentrate in regions of Jingning, Chongxin, and Jingchuan.The short-time heavy precipitation events occur most frequently in August, concentrating in the Kongtong mountainous areas in the northern Pingliang and the valley areas of the southern Chongxin.The diurnal variation of short-term heavy precipitation in June is characterized by a unimodal pattern, with the peaks occurring mostly in the afternoon.The hourly precipitation within the range of 20-30 mm occurs most frequently, accounting for more than 80% in June.The diurnal variation of short-term heavy precipitation in July and August shows a multi-peak pattern and occurs more frequently at the night.The frequency of hourly precipitation exceeding 30 mm increases significantly, accounting for about 40% in July and August.Three synoptic patterns contributing to short-time heavy precipitation in Pingliang are classified, including the upper-level low trough pattern, the subtropical high-pressure pattern, and the northwesterly airflow pattern.In addition, we find that some average proper values for physical quantities such as the K index, CAPE, T₈₅₀-T₅₀₀, Q₈₅₀, θ_se-850 have good indicative significance for heavy precipitation forecast in Pingliang after the statistical analysis on the environmental parameters that represent the thermodynamic, moisture, and unstable conditions.

Key words: Short-time heavy precipitation, Influencing weather system, Physical quantity