一次江淮飑线天气过程的边界层湍流输送特征

Characteristics of boundary-layer turbulent transfer during a squall line over Jianghuai region

为了充分了解飑线冷池、湍流动能及湍流输送的特征,利用中尺度天气预报数值模式,对2014年7月12日江淮地区的一次飑线过程进行了数值模拟,分析其边界层冷池、湍流动能和湍流输送特征。结果表明:飑线处于发展期时冷池作用较小,随着飑线系统的增强,冷池作用逐渐显著,对环境风的阻碍作用加强,其前沿辐合加强,有利于触发新对流;飑线发生前,浮力项为边界层湍流动能的主要产生项,湍能随高度减小;飑线系统过境时,切变项为主要湍能源,在边界层高层时较大;飑线对流前的晴空区域内,边界层湍流运动向下输送动量,补充边界层摩擦损耗;飑线强对流影响的区域内,近地层湍流运动向上输送动量,减弱了大风的影响;向上较大的潜热、感热通量增强低层的大气不稳定性,有利于强对流系统的发生发展。分析表明,边界层湍流输送与飑线系统的演变过程密切相关。

To fully understand the characteristics of cold pool,turbulent kinetic energy and turbulence transfer,a squall line case that occurred on 12 July 2014was simulated,based on weather research and forecasting model（WRF）mesoscale numerical model.The major results are as follows：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 cuts off environmental inflow that causes the strengthening of convergence,which is beneficial to trigger new convection.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 up-ward,which weakens the influence of the squall line winds.Large positive latent heat,flux increases the instability in the lower atmosphere,which is conducive to the occurrence of strong convection system.Analysis shows that the evolution process of boundary layer turbulent transport and squall line systems are closely related.