Numerical Simulation And Characteristic Analysis On Boundary-Layer Turbulent Flux Transfer Of A Squall Line In Jianghuai Region

In order to research the squall line over Jianghuai region, the the vertical structural features, some characteristics of cold pool, turbulent kinetic energy and turbulence transfer during a squall line case occurred on 12 July 2014 was investigated, based on WRF mesoscale numerical model. The major results are as follows:(1) The process belongs to the"Caoqian"type of squall line. The squall line formed in a broad region which is on the southern side of shear line and the north side of the low-level jet. Zonal distribution of precipitation has obvious characteristics of mesoscale. There are several rainstorm center which move from west to east over time. (2) The southwest low-level jet transport a large mount of water vapor to the convection zone. Potential pseudo-equivalent temperature contour are Intensive in the squall line convection zone which provides unstable energy for the system. (3) low-level convergence and high-level divergence intensify upward motion largely which promotes the development of new convection cell In the front of the squall line system; Low level divergence anticyclonic vorticity type area corresponding to the squall line thunderstorm high pressure and high-level convergence cyclonic vorticity area inhibit the development of the strong convection in the squall line convection main body. Old convection cell weakening and new convection cell strengthen at the squall line systems frontier which make the squall line systems moving forward. (4) There is a weak cold pool during the initial period of squall line development. With the development of the squall line systems,the cold pool is enhanced. A strong cold pool cut off environmental inflow that cause the strengthening of convergence, which is beneficial to trigger new convection. Gust front moves faster than the convective body which hinders southern warm moist air flows at the squall line system dissipation phase. (5) The boundary layer turbulence kinetic energy characteristics and main turbulent energy is different in different development period of the squall line. Before the squall line breaking out, buoyancy term is the main item of boundary layer turbulence kinetic energy and turbulence kinetic energy decreases with height. While after the squall line breaking out, shear term is the main item of turbulence kinetic energy and larger in the upper boundary layer. Boundary layer turbulent momentum transfer in the clear sky area is downward,which makes up for the boundary layer friction loss. In the area affected by the squall line, surface layer turbulent momentum transport is upward, which weakens the influence of the squall line winds. (6) Large positive latent heat, sensible heat flux increase instability in the lower atmosphere, which is conducive to the occurrence of strong convection system. Large positive sensible heat flux and latent heat flux decreasing which is not favorable to the development of convection in the mature stage; The latent heat is strengthening in front of the convection which is not conducive to convection to dissipate in the dissipation phase.