Observation Analysis And Numerical Modeling Of A Mesoscale Convective Vortex

Mesoscale Convective Vortex (MCV) is a heat topic in mesoscale meteorology of recent thirty years. With consistent researching in recent thirty years, mesoscale meteorologists have gradually caught its basic characters, evolution mechanism and its relationship with high-impact weather systems. Although there has been a lot of work regarding MCV, the work to summarize those former researches is really seldom. The first chapter of this thesis is based on my personal understanding of this topic after reading MCV papers to summarize the advance of MCV research in the recent thirty years. This summary includes the following aspects:(1) the basic characteristics of MCV,(2) the reason of MCV’s genesis and MCV’s conceptual model,(3) the impact of balanced motion of MCV on the secondary convection,(4) climatology of MCV,(5) MCV in BAMEX,(6) MCV’s impact on TC genesis,(7) MCV’s impact on Extratropical Explosive Cyclone,(8) MCV on mei-yu front.For the MCV researches in the recent thirty years mainly focusing on the MCV on the U. S. continent, researches regarding MCV on Eastern China are really seldom, but the MCVs on Eastern China, especially those in the mei-yu season, always belong to the topic that many people concerns about. The aim of this thesis is to investigate the MCV in mei-yu season based on the former researches and methods. There are many kinds of MCVs, and the one investigated in this thesis belongs to the typical stratiform embedded MCV. When the MCV reached its mature stage, it could trigger secondary convection on its downshear side, and the secondary convection in turn feed back to the MCV and made it amplified and penetrated to the surface, and the maximum circulation of this MCV finally moved down to the low-levels. The second chapter of this thesis bases on the reanalysis data and routine observation data to mainly investigate the basic structure and characteristics of this MCV, including:(1) the synoptic background of the MCV,(2) the evolution process and vertical structure of the MCV,(3) the vorticity budget of the MCV,(4) deformation field’s impact on the shape of MCV. The third chapter will adopt the WRF model to simulate this MCV event, and investigate its mechanism of genesis and evolution and the probable reason of the triggering of the secondary convection from the following aspects:(1) vorticity budget,(2) temperature budget,(3) energy budget,(4) local Rossby radius of deformation,(5) the isentropic vertical motion of the MCV.This MCV belonged to the typical stratiform-embedded MCV. The north part of it is convection inhibition region, while the south part of it is convection active region. The change of MCV’s shape has close relationship with the background deformation field. This MCV originated in the north of the parent MCS. After the dissipation of the parent MCS, the MCV still lasted and triggered secondary convection on its downshear side. Those retriggered convection gradually evolved into MCS, and the secondary MCS re-intensified the MCV. The body of the re-intensified MCV extended up to the uplevels and penetrated down to the low levels. Although the body of the MCV remained in the midlevel, its maximum cyclonic circulation moved down to the surface. The cyclonic circulation in the midlevel resulted from the midlevel stretching, and the low level cyclonic circulation was induced by the low level eddy flux. The contribution of tilting was quite small, so it could not make obvious effect to the MCV.During the convective period, the latent heating released by microphysics scheme and cumulus scheme was the main reason of the uplevel warming. This warming increased the midlevel PV. When convection ceased, the cooling effect of the collapsed MCS enforced the surface cool pool, and this enforced cool pool would intensify the low-level PV. Hence, the final result of the increased midlevel and low-level PV was penetration of the MCV.The energy budget revealed that it is the latent energy that drove the MCV. The latent energy released by convection first conversed into eddy potential energy. The energy conversion from eddy potential energy to eddy kinematic energy was realized by vertical motion, and the enforced upward motion induced the midlevel convergence which formed the MCV by its stretching effect. Although the zonal kinematic energy also could increase the midlevel eddy kinematic, the rotation of the MCV was still disturbed by transporting horizontal momentum into the MCV region.It was the MCV that reduced the local Rossby radius of deformation. When the local Rossby radius of deformation was smaller than the radius of a local heat source (the radius of MCS), the MCS was dynamically large and the atmospheric response was dominated by the inertial mode which was helpful for MCV’s sustainment.With proper vertical wind shear, secondary convection formed on the downshear side of the MCV. The secondary convection was triggered by isentropic vertical motion when environmental wind flowed from warm area to cold area. When the isentropic lifting motion was broad and organized, the broad and organized MCS would be triggered; on the other hand, when the isentropic lifting motion was limited and scattered, the convection was also scattered.