Numerical Study Of Cold Vortex Over Northeastern China And The Analysis Of Vertical Motion

The cold vortex, one of the main weather systems over northeastern China, could cause severe weather, such as the heavy rainfall, hailstone, strong wind and etc. Therefore, the study of cold vortex over Northeast China is very important. However, the precipitation area of cold vortex is uniform distribution, and the main rainfall area is not in the center of cold vortex. The purpose of this paper is to analyze the structure of Mesoscle Convective System (MCS) and the reasons of its rainfall in the cold vortex.Using the WRF/ARW model simulate a proceeding of cold vortex over Northeast China on July 7-12,2007. The simulations of 24 hour rainfall and the MCS rainfall could reflect the observed results. Thus the analyses of the proceeding are based on the simulation results. The analysis of synoptic weather indicates that the cold air mass above the north of Lake Baikal moves to the cold vortex over Northeast China and enforces it. What's more, a part of the cold air transfers to the mid and lower part of troposphere from tropopause, which causes the process of dry intrusion. Besides, in the east of cold vortex, there is the convergence of water vapor transport, which indicates the plenty water vapor at the place. The above shows that the intersection of the cold dry air and the warm wet air benefits the formulation of rainfall. The results of wind structure of mesoscale convective system prove that the southeast and northeast parts of cold vortex, the prone areas of MCS, are the maximum of cyclonic curvature. At the maximum of cyclonic curvature, there is the severe horizontal convergence of wind, which could lead to the heavy rainfall.To calculate the vertical motion, two methods including the kinematical method and the adiabatic method are used in this paper. Through analyzing the results of two methods for calculating the vertical motion, it is shown that the kinematical method is better for mesoscale movement than the adiabatic method. Then the kinematical method is used in this paper to calculate the vertical motion of MCS. From the vertical motion of MCS, it is shown that there is convergence at the maximum of cyclonic curvature in the lower troposphere and upward vertical motion, which benefits to the formulation and development of rainfall. Finally, using the vertical component of convective vorticity (CW) diagnoses the location of MCS rainfall, and the corresponding of CW and rainfall shows that CW could indicate the area of rainfall.