干冷空气入侵台风“海棠”残余低压引发的华北地区大暴雨分析

Analysis of the heavy rain in North China for dry cold air intruding into typhoon"Begonia"depression

利用地面逐小时观测资料、NCEP/NCAR(1°×1°)再分析资料、FY-2F卫星加密观测(6 min分辨率)的云顶亮温(TBB)和常规观测资料,对1710号台风"海棠"残余低压北上与冷空气结合导致华北东部大暴雨天气过程进行分析。结果表明:(1)该华北东部大暴雨过程分为两个主要时段,2017年8月1日23时-2日20时(北京时)华北东南部暴雨,由台风残余低压产生,8月2日20时-3日11时华北东北部暴雨,是由减弱变性的台风环流与西风槽东移带来的干冷空气结合进而导致新生气旋和低涡产生引起。(2)8月2日20时,台风与冷空气逐渐结合,干冷空气从对流层中高层进入变性台风北部,造成位涡下传,进而导致对流层低层形成低涡、地面形成新生气旋,同时激发出中尺度对流系统,系统稳定发展并缓慢向东北方向移动,导致持续近5 h的短时强降雨。(3)暴雨水汽来源主要有两部分,一是台风本身携带来的由南风输送的水汽,二是来自黄渤海由东风输送的水汽,二者结合后从对流层低层将水汽带至华北东北部,且在燕山前形成了水汽强辐合,为该暴雨过程大提供充足的水汽条件。

Based on surface-observed hourly data,NCEP/NCAR(1°×1°)reanalysis data,black body equivalent temperature(TBB)of FY-2F satellite(6 minutes)and conventional observation data,we analyzed the heavy rains in the eastern of North China caused by the com⁃bination of the cold air mass and the 1710 typhoon"Begonia"depression after it moved north.The results show that:(1)The rainstorm in eastern of North China was divided into two main periods.The heavy rain in the southeastern part of the North China was caused by the ty⁃phoon residual low pressure from 23∶00 BT 1 to 20∶00 BT 2 August.However,the weakened and denatured typhoon circulation combined with the dry and cold air brought about by the eastward movement of the westerly trough and resulted in the regeneration of ground cyclones and low vortices from 20∶00 BT 2 to 08∶00 BT 3 August,which eventually led to heavy rains in northeastern part of North China.(2)At 20∶00 BT 2 August,the typhoon was gradually combined with the cold air,and the dry cold air entered the northern part of the typhoon from the mid-level and high-level of the troposphere,causing a downward spiral of the potential vortices and forming a low vortex in the lower tro⁃posphere and a new cyclone on the ground.At the same time,the mesoscale convection system was excited,and it developed steadily and moved slowly to the northeast,resulting in a short period of heavy rainfall that lasted for nearly 5 hours.(3)The source of the water vapor in this heavy rain event mainly consisted of two parts.Some of the water vapor was carried by the typhoon itself,which was transported by the south wind.Another part of the water vapor was from the Yellow Sea and the Bohai Sea,which was transported by the east wind.The two parts of the water vapor were combined to bring the water vapor to the northeastern part of North China through the lower troposphere.The strong convergence of water vapor occurred in front of the Yanshan Mountains,providing abundant water vapor supply for the rainstorm.