弱天气尺度下短时强降水环境特征和触发机制研究--以河北省廊坊市为例

Environmental Characteristics and Triggering Mechanism of Local Short-term Heavy Precipitation at Weak Synoptic Scale

利用河北省廊坊市2010—2018年5—8月地面自动站逐时降雨量、加密观测资料和北京探空资料,分析弱天气尺度下廊坊春夏季局地短时强降水时空分布特点、中小尺度触发机制和环境特征参数并归纳预警阈值.结果表明:2010—2018年弱天气尺度下局地短时强降水过程发生13次,且多发生在下午到傍晚和后半夜,大厂回族自治县发生局地短时强降水的次数最多;归纳环境参数的预警阈值,其中850 hPa比湿、700 hPa比湿、850 hPa与500 hPa温差、对流有效位能、K指数、0~6 km垂直风切变和暖云层厚度选取25%分位值作为最低阈值,取值分别是9 g/kg、5 g/kg、23℃、586 J/kg、33℃、4.3 m/s和3.2 km;500 hPa比湿、对流抑制能量和SI指数选取75%分位值作为最高阈值,取值分别是3 g/kg、141 J/kg和-0.4℃;在平直西风环流型和高压脊型两种弱天气尺度环流背景下,廊坊市短时强降水的触发机制主要有地面辐合线、负变压和热力因子.

The temporal and spatial distribution characteristics of local short-time heavy precipitation in spring and summer in Langfang City under weak weather scale were analyzed by using hourly rainfall data of automatic ground stations,intensive observation data and Beijing radiosonde data from May to August during 2010-2018,and then the triggering mechanism,environmental characteristic parameters of small and medium-sized scale,and the warning threshold were analyzed and summarized.The results showed that there were only 13 cases of local shorttime heavy rainfall under the weak synoptic scale,most of which occurred from afternoon to evening and late midnight.Dachang Hui Autonomous County had the highest frequency of local short-time heavy rainfall.Inductive environment parameters of early warning threshold,of which 850 hPa specific humidity,700 hPa specific humidity,temperature difference between 850 hPa and 500 hPa,convective available potential energy,K index,0 to 6 km vertical wind shear and warm clouds thickness selecting 25%quartile as a minimum threshold,the values are 9 g/kg,5 g/kg,586 J/kg,33℃and 4.3 m/s and 3.2 km respectively.500 hPa specific humidity,convection inhibition energy and SI 75%quartile value as the highest threshold,the values were 3 g/kg,141 J/kg and-0.4℃,respectively.Under the background of two weak synoptic scale circulation types,namely straight westerly circulation type and highpressure ridge circulation type,the triggering mechanism of short-time strong inflow in Langfang City includes surface convergence line,negative variable pressure,and thermal factors.