陇东地区8月一次暴雨、强对流天气特征及成因分析

Characteristics and Causes of a Heavy Rain,Strong Convective Weather in Longdong Region in August

为了提高陇东地区夏季暴雨的预报水平,应用常规地面、高空观测、FY-2F卫星TBB资料与NCEP/NCAR逐6小时资料,对甘肃省庆阳市2015年8月2日出现的区域性强对流、暴雨天气过程进行诊断分析,结果表明:这是一次较罕见的前倾槽西北气流型暴雨过程,500 h Pa高度上有冷空气沿冷槽下滑,700 h Pa有暖中心,低层暖湿阻碍了冷空气下滑,形成前倾槽;基于庆阳市短时强降水中尺度分型,本次天气过程属于西北气流型,700 h Pa低涡、"人字形"切变线及地面辐合线为暴雨的主要触发机制;极强的热力不稳定对该类暴雨预报具有较好的指示意义,过程期间陇东中南部K指数>36℃,CAPE值>1000 J/kg,沙氏指数<-2的区域与暴雨落区相吻合;暴雨前期700 h Pa高度上陇东地区为比湿>10g·kg^(-1)的高湿区,大于预报经验值8 g·kg^(-1),湿层深厚,来自孟加拉湾的西南气流和台风外围偏南气流为暴雨区输送水汽,水汽在陇东东南部辐合;在垂直方向上,水汽和能量在中低层辐合、高层辐散,庆阳市上空从低层到高层均为垂直上升运动,且最大值中心位于500 h Pa高度;卫星云图上可看出本次降水是冷锋云系尾部的两块对流云团合并加强所形成的β中尺度对流云团产生的,云顶亮温达-80℃以下;对该类较罕见暴雨类型的分析可为陇东地区暴雨预报及防灾减灾提供参考依据。

In order to improve the forecast of summer heavy rainsfull, the data of conventional ground, high altitude ob- servation, FY-2F satellite TBB data and NCEP / NCAR 6-hour data had been used to diagnosis and analysis of regional severe convective and rainstorm weather happened on August 2, 2015, Qingyang area, Gansu province. The results show that：This is a relatively rare forward trough northwest airflow type rainstorm process. Cold air drops along of the cold trough at the height of 500 hPa. Longdong is located in front of the tank with a warm center of 500 hPa. As the lower layer of warm moisture prevents the upper air from sliding into the forward trough;Based on the mesoscale classification of short-term heavy precipitation in Qingyang, this weather process belongs to the northwest airflow type, 700 hPa low vortexes, ＂herringbone＂ shear lines and ground convergence lines are the main triggering mechanisms of rainstorm. Ex-tremely strong thermal instability has a good indication of this type of heavy rainfull forecast, during the process,K index 〉36 ℃ ,CAPE〉1000 J/kg in Longdong south-central, and the area of SI〈-2 is consistent with the rainstorm zone. Prior to the occurrence of the rainstorm, the area above the longdong area of 700 hPa was the high wet area of 〉10 g · kg^-1 , which greater than the predicted experience value of 8 g · kg^-1. Southwest airflow from the Bay of Bengal and the south airflow of typhoon outside transported water vapor for the rainstorm area. Water vapor converged in the southeastern part of Qingyang. In the vertical direction, the water vapor and energy converged in the low-level and diverged in the high- level. From the lower to the upper of atmosphere moved upward, and the maximum center of the rising movement was at 500 hPa height. It can be seen from the satellite image that the precipitation is the result of β mesoscale convective clouds that was developed by two convective cloud clusters in the tail of the cold front cloud system, and the ceiling of the cloud reached -80 ℃. The analysis of this type of rainstorm is a reference for the forecast of rainstorm and disaster pre-vention and reduction in Longdong.