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

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.