2015年冀中廊坊短时强降水的风场垂直结构特征

Vertical Structure Characteristics of Wind Field in Short-time Severe Rainfall in Langfang,Central Hebei Province in 2015

利用MICAPS、自动气象观测站、风廓线雷达资料和NCEP再分析资料,综合分析了2015年出现在廊坊市的短时强降水天气过程及降水开始前大气的风场特征。结果表明:(1)低空急流早于短时强降水6~114 min出现,平均提前量约46 min;强降水结束时,低空风向发生显著变化,由西南风迅速转为偏东风或西北风。(2)在强降水发生前的1 h,低空急流指数突增,极值达到46.3 m·s^(-1)·km^(-1),雨强减小至20 mm·h^(-1)后,平均低空急流指数迅速跌至1.3 m·s^(-1)·km^(-1)。(3)低空风切变指数增大约早于强降水1 h出现,极值可达0.139 s^(-1),达到了中等强度风切变。(4)上升气流早于强降水发生前约90 min出现,表明西南气流携带的水汽和能量开始在降水地区被强迫抬升,此后的约30 min上升气流达到最强盛,在强降水开始前60 min内高度抬升,厚度减小,强度迅速减小,直至降水开始后下沉气流占据绝对主导地位。

By using MICAPS,automatic station data,wind profiling radar data and NCEP 6 hourly reanalysis data,the short-time severe rainfall weather characteristics in Langfang,Hebei province,in 2015 and the wind field characteristics of the atmosphere before the intense precipitation are analyzed synthetically.The results show that:(1)the low-level jet appeared 6114 min earlier than the short-time severe precipitation occurred,and the average lead time was about 46 min.At the end of severe rainfall,the low-altitude wind direction changed significantly from southeast to east or northwest.(2)An hour before the intense precipitation,the low-level jet index rose up abruptly,with the extreme value reaching 46.3 m·s^(-1)·km^(-1),but after the rainfall intensity decreased to 20 mm·h^(-1),the average low-altitude jet index rapidly dropped to 1.3 m·s^(-1)·km^(-1).(3)The increase of low-altitude wind shear index occurred about 1 h earlier than the occurrence of intense rainfall,and the extreme value reached 0.139 s^(-1),which indicates that the moderate wind shear was achieved.(4)Updraft occurred about 90 min before the severe rainfall,which denotes that water vapor and energy carried by southwest airflow began to be forced up in the severe precipitation location.About 30 min later,the updraft developed to be strongest.Within 60 min before the heavy precipitation,the updraft’s height increased,thickness decreased and intensity decreased rapidly,then downdraft became dominant until the start of precipitation.