一次江淮暴雨中中尺度低涡的数值模拟及分析

Numerical Simulation of a Mesoscale Vortex in a HeavyRain Process in Changjiang-Huaihe River Basin

利用MM5模式对2003年7月4—5日一次江淮梅雨暴雨过程进行了数值模拟。分析表明:暴雨与江淮地区对流层中低层中尺度低涡的发生发展有密切关系。中尺度低涡与中尺度雨团相伴移动,低涡强度与雨强的演变近于一致;低涡中心的强上升运动及低层辐合、高层辐散的配置有利于中尺度对流系统的发生发展;低涡低层有不稳定能量的积聚。应用螺旋度理论分析指出,较大的螺旋度是对流层中低层低涡发生和发展的一种有利机制。

The heavy rain occurred from 2000BST July 4 to 2000BST July 5,2003 in the Yangtze-Huaihe River Basin was simulated by the mesoscale numerical model MM5.The analysis suggests that the heavy rain event was close related to the generation and development of a mesoscale vortex in the mid-low troposphere.The vortex moved together with a mesoscale rain cluster,and its intensity was in agreement with the evolution of precipitation intesity at the center of the rain cluster.The disposition of the intensive ascending motion at the center of the vortex,the lower-level convergence and upper-level divergence,and the accumulation of unstable energy in the low level of the vortex were very favorable for the generation and development of the mesoscale vortex.It was found that the higher helicity in the mid-low troposphere might be one of the possible mechanisms for the generation and development of the mesoscale vortex.