2015—2019年甘肃平凉地区夏季短时强降水时空分布及天气形势特征

选取了甘肃平凉地区2015-2019年6-8月发生的27次短时强降水事件。利用自动站逐小时降水资料和高空探测资料，按照短时强降水阈值分类统计法和常规天气分析方法对甘肃平凉地区夏季短时强降水时空分布、影响天气系统及大气环境背景进行了统计分析。结果表明：6月短时强降水频次少，强降水高发区为六盘山山区；7月频次明显增多，活跃地区为静宁、崇信、泾川一带；8月频次及强度达到峰值，密集区为平凉北部的崆峒山区、崇信南部河谷地带。6月短时强降水日变化呈现单峰型特征，以午后居多，1 h降水量在20-30 mm段发生频次最高，占6月频次的80%以上；7月和8月日变化呈多峰型结构，夜间短时强降水频次增多，1 h降水量大于30 mm的频次显著增加，约占7月和8月总频次的40%。分析总结了平凉地区短时强降水天气类型，即高空低槽类、副热带高压类、西北气流类。另外，对表征动力、水汽、不稳定条件的环境参数统计分析，结果显示K指数、CAPE、T₈₅₀-T₅₀₀、Q₈₅₀、θ_se-850等物理量平均特征值对平凉地区强降水预报有较好的指示意义。

Spatiotemporal distribution of short-term heavy precipitation and characteristics of synoptic condition during summer in Pingliang,Gansu province from 2015 to 2019

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.