中国东部地区一个中尺度对流涡旋的涡度收支分析

中尺度对流涡旋(MCV),与其他中尺度涡旋不同,有着其独特的动力机制与发展途径.一旦MCV形成,极易产生灾害性天气过程.为了解我国的MCV,使用非静力中尺度模式天气预报和研究模式对中国东部2003年7月4至5日降水过程进行了高分辨率的双向三重嵌套的数值模拟.与观测资料比较,模拟结果较为准确地再现了当时的大气状况.采用了空间滤波的方法对模式结果进行了大尺度背景场与中尺度扰动场的尺度分离,对MCV的结构与移动进行分析,并追随MCV的活动对其的涡度收支情况进行诊断分析.分析表明,大尺度背景场与中尺度扰动场对MCV的作用有着明显的差异.MCV的移动由大尺度背景风场引导;其中辐合作用直接决定了MCV的形成与发展,大尺度水平运动对中尺度涡度的水平输送为水平平流项的主要部分.而由垂直风速的水平变化所导致的水平涡度的倾斜作用在此MCV形成与发展阶段作用并不明显.成熟时的MCV与成熟时的中尺度对流复合体类似有着3个明显的环流,在对流层高层与低层均为辐散反气旋性环流,对流层中层则为较为深厚的气旋性环流.

A Vorticity Budget for a Mesoscale Convective Vortex over East China

The mesoscale convective vortex(MCV),which is one kind of mesoscale vortexs,has the unique dynamical mechanism.Once the MCV is formed,there will be very high possibility of the mesoscale severe disaster weather.There may be some difference between the MCV in the China and in the United States.A heavy rainfall,which was correlative with an MCV system,occurred in the east of China from 4 to 5 July 2003 which provided an opportunity to get some information of the MCV in China.The high-resolution weather research and forecast model,a new generation of mesoscale numerical weather forecast model,was used to get the particular atmosphere status about the MCV.In the simulation,the WRF model was run with three two-way nested grids of 45/15/5 km grid spacing.A comparison of model simulations with observations suggests that the simulation was quite successful and credible,and it might provide a high-resolution,dynamically consistent dataset for us to further analyze.A spatial bandpass filter was performed to divide the wind into mesoscale and synoptic components and the response function was chosen to capture 95% of the signals of phenomena with wavelengths of 300 km which was close to the horizontal range of the MCV.The scale-discriminating of the wind made the mesoscale current much more distincts.Diagnose results suggest that both the synoptic background wind and the mesoscale perturbation wind have the distinct effects on the MCV.The movement of the MCV is decided by the synoptic wind.The convergence of both synoptic and mesoscale vorticity is the largest contribution to vorticity tendency,and apparently,they are the main source to inspire and develop the MCV.The tendency from horizontal advection is mainly due to the advection of the mesoscale vorticity by the large scale wind,and the tendency from vertical advaction is mainly due to the the advection of the large scale vorticity by the mesoscale motion.Tilting of horizontal vorticity by horizontally varying vertical wind nearly does not play the role on resolved scales,which is very different from the case in the United States. Like the mature mesoscale convective complex,there are three distinct mesoscale circulations associated with mature MCV.The upper layer and the boundary layer are both characterized by divergent anticyclonic circulations,while the midlevel is associated with a deep,cyclonic circulation.