“灿鸿”台风造成浙江东北部大暴雨成因分析

摘要

本文利用常规观测和自动站加密资料、卫星云图资料及NCEP 再分析资料，分析了2015年7月10—11日1509号台风灿鸿造成其西侧浙江东北部异常强暴雨事件，得到本次大暴雨过程是由于“灿鸿”强度强、范围大、直接影响时间长，长时间东北气流下，在浙东北特殊地形作用下，形成地面辐合带造成的。台风影响前期该区域处在对流不稳定状态，水汽含量丰沛，低层辐合，高层辐散且气温低，有利于上升运动，上层水汽冷凝造成强降雨。暴雨区低层 MP V 1由负值转变为正值，导致垂直涡度加强，925 hPaθse的高能区的长期存在，有利于上升气流增强，水汽长时间大量输送有利于台风的发展和维持，也有利于强降雨的形成。这些物理量的变化与雨量增大和减小有6～12 h 的提前。呈喇叭口状的杭州湾及南面四明山、狭长东北—西南走向的象山港以及南岸的山脉等地形有迎风坡作用和地形辐合，对东北气流参与造成的降雨有增幅作用。%This paper analyzes the cause of the extremely heavy rainfall in northeastern Zhejiang induced by Typhoon Chan-Hom (1509)from 10 to 11 July 2015 by using conventional observation,AWS data,satel-lite and NECP reanalysis data.The results show that under the effect of the special terrain in northeast of Zhejiang,strong intensity and wild impaction of Chan-Hom meeting with the long-time northeast airflow contributed for this heavy rain process.During the early stage of the Chan-Hom impact,this area was in a state of convective instability.Besides,the abundant water vapor,low-level convergence and upper-level divergence provided a beneficial condition for the heavy rainfall.In the rainstorm areas,the MPV1 changed from negative to positive at low level,leading to an increase of vertical vorticity.The long-time mainte-nance of the highθse energy region at 925 hPa also benefited the updraft.The long-time transportation of water vapor was not only favorable for Chan-Hom’s maintenance,but also beneficial to the formation of the heavy rainfall.There was a positive correlation of 6-12 h in advance for the increasing and decreasing of the heavy rainfall with the vapor transportation,surface convergence zone andθse at 925 hPa.And the special topography enhanced the heavy rainfall supported by the northeast airflow because of the effects of the upslope and terrain convergence,which were formed by the trumpet-shaped terrain of Hangzhou Bay, Siming Mountain,elongated northeast-southwest Xiangshan Harbor and its southern mountains.