山东半岛南部一次沿海强降雨成因分析

利用常规气象观测资料、区域自动站观测资料、NCEP/NCAR 1°×1°再分析资料和雷达探测等资料,对2012年9月21日山东半岛南部沿海强降雨过程的成因进行了天气学诊断分析,结果表明:1强降雨是在500hPa第1个西风槽过后第2个西风槽逼近的过程中产生的,850hPa以下为偏南的向岸风,且风速随时间增大,形成偏南的超低空急流,持续地向沿海输送水汽和能量,造成水汽辐合、湿度增大、对流有效位能升高。产生强降雨的水汽和不稳定能量条件远小于内陆地区。2在向岸的超低空急流的左侧产生中小尺度的涡旋和辐合上升,海岸地形抬升作用使得上升运动加强,触发对流不稳定能量释放,造成强降水。3在雷达回波中,小尺度的对流单体沿海岸线向西南方向发展,后期在日照附近的沿海形成弓状回波,向东南海区移动。

Causal Analysis of a Heavy Rain along Southern Shandong Peninsula Coast

By using the data of conventional observation, NCEP/NCAR 1°×1° reanalysis, and radar echo, a persistent heavy rain occurred on the southern coast of the Shandong Peninsula on 21 September 2012 is diagnosed and analyzed. The results show: (1) The heavy rainfall was affected by the westerly trough at 500 hPa when the first westerly trough passed and the second westerly trough was moving toward the area. Beneath 850 hPa was the southern winds toward the shore, and the wind speed increased with time so that south wind jet was formed below 925 hPa, which transported water vapor and energy and caused water vapor convergence, increased humidity and convective instability energy. The moisture and instability condition of producing heavy rainfall were smaller than those in inland. (2) The mesoscale vortex and convergence ascending motion were formed on the left side of the shoreward wind ultra low level jet. The effect of seaboard topographic lifting impelled ascending movement to increase, which triggered the instability energy releasing, leading to strong rainfall. (3) In radar echoes, small scale convective cells grew along the coastline toward southwest, and bow shaped echoes formed along the coast near Rizhao in the later period, and moved toward the southeast sea area.