弱冷空气与台风残留低压相互作用对一次大暴雨过程的影响

本文利用多普勒雷达资料、中尺度自动站雨量资料,结合经过控制试验的高精度数值模拟输出的诊断物理量,研究了2010年＂莫兰蒂＂台风低压环流在浙江中北部地区引发的大暴雨天气过程的物理原因。结果表明：这次大暴雨过程主要由＂莫兰蒂＂残留云系、副高边缘的暖湿气流和北方的弱冷空气共同影响产生,降水回波为积层混合性降水回波,降水效率高;杭州地区多个中小尺度系统的相互作用使得对流云团在该地区持续加强和发展,而强降水中心附近风速的加强和面积的扩大,使整个降水时段内不断有水汽输入降水区,为降水提供了丰沛的水汽条件;对流层中低层正的垂直螺旋度,低层负湿位涡区和中高层正湿位涡区的配置形成的不稳定能量在弱冷空气入侵时有利于造成较强烈的中尺度上升运动,加上降水引起的潜热释放对中高层空气的加热作用,从而能够形成持续的抽吸作用。这些条件能引起持续性的强降水,导致了杭州地区暴雨的发生。研究此次大暴雨过程,对预报有一定的指示意义。

The Effect of the Interaction Between Weak Cold Flow and Typhoon Depression on a Rainstorm

The heavy rainstorm resulting from depression circulation of typhoon Meranti is studied with the analysis of Doppler radar reflectivity, mesoscale observational data and the diagnosis of the simulation results from the mesoscale numerical weather research and forecasting model (WRF). The main results show that the remained cloud system of Meranti, the warm and moist flows in the border of subtropical high and the weaker cold air from higher altitudes are responsible for this rainstorm. The precipitation radar reflectivity consists of cumulus and stratus, which can produce more precipitation amounts than a unique kind cloud. The interaction among several meso and micro scale convective systems is advantageous to the development of local convective cloud cluster, and the wind velocity zone occurs with the enhancement in the intensity and area of wind velocity. During the period of rainfall, the moist condition for precipitation is satisfied with the moist transporting into the rainfall region. The configuration of the vertical helicity at mid and low levels, the strong ascending movement resulting from the invasion of the weak cold air into the air column where the negative moist potential vorticity is at low levels and the positive moist potential vorticity is at middle and upper levels, and the heating effect coming from the latent heat release made a sustained pumping action, which leads to the standing raining and forms the rainstorm in Hangzhou. This can be an index for forecasting tropical cyclone local rainstorm.