Diagnosis On The Structure Evolution And Total Lightning Activity Of Two Types Severe Convective Systems On West-Coast Area Of Bohai Bay

There are mainly two types of severe convective weather in China:one is mainly with the convective torrential rain, which the influence scope is broad, and the other is mainly with hail and thunderstorm wind, changing dramatically and influencing small scope. The α-Mesoscale Convective System (MαCS), one of the systems corresponding to the former, lasts for more than six hours long. The multi-cell thunderstorm or supercell thunderstorm (i.e. α or γ Mesoscale convective system, MβCS or MγCS), most of the systems corresponding to the later, continues only for0.5-4hours long. The environmental condition of two kinds of severe convective weather is different significantly. MaCS needs adequate water supply, while the thunderstorm system requires severe convection effective potential and shear of vertical wind. Moreover, the two types can be distinguished from the view of space, thermal and dynamic structure and organization evolution mechanism. In addition, the severe convective system is composed of convection cell, in which existing the dynamic field, the microscopic field and the electric field having interaction between each other, respectively. In this paper, basing on observation data, using statistical analysis and diagnostic analysis of the case, in the particular geographical environment along the Bohai Sea, the multi-scale structure and formation mechanism of quasi-circle MaCS and multi-cell thunderstorms are researched, especially lightning activity characteristic, charge structure and its relationship with structure change of the severe convective system are analyzed. The content and conclusions of the study are as follows:1. Easterly airflow from the Yellow Sea and the Bohai Sea isa close relationship between the easterly winds and the heavy rain occurred in Tianjin. It is proved that the presence of the Yellow Sea and the Bohai Sea promotes the larger center range and the strengthener magnitude of the convective rainstorm, causing by the quasi-circle M a CS. It can be classified into two types including the triggering type and the touching type, and the landing sea breeze matches with unstable region triggering or strengthening the thunderstorm system. The original convection system will be strongly developed causing by merging with other convective system as a result of vapor, convergence uplift and so on.2. There are positive vorticity, divergence, cold, anti-cyclone mesoscale disturbance circulation in the MaCS high level (center in200hPa), while negative vorticity, convergence, warm heart below400hPa-900hPa. The cloud top of the mature MaCS is characterized by quasi-circle, clear and smooth boundary and compact structure relating to the mesoscale anticyclone disturbance flow field existing at200hPa. However, there is not clear and complete mesoscale cyclone disturbance flow field at700hPa. The physical reasons are diverse for different merge types.3. The correlation coefficient between total flash frequency (ground lightning and cloud flash) with Set11is0.79in multi-cell hailstorm. The correlation coefficient of ground flash frequency, cloud flash frequency and upV40-6is between0.63-0.97. In the exuberant phase, H of GUAN convection cell is different with others, the H is lower and positive CG has larger proportion.4. Regardless of the merger between MβCS, or the merger between MγCS within MβCS, or the merger between convective cells during multi-cell thunderstorm evolution, all of them can be described by the radar parameters (upV40-6, upFV40-6, down FV40-6). The strength and scope of the whole system enhancements after the merger, and the strength of updraft weaken at the moment (6-12min) with the system collapsing. Along with the merger, the height (H) of main positive charge region declines while lightning frequency changes slightly.