对流边界层发展受覆盖逆温影响的大涡模拟研究

Impact of capping inversion on development of convective boundary layer:evaluating the parameterization of entrainment rate through large-eddy simulation

本文运用大涡模拟方法研究了存在覆盖逆温时对流边界层顶部的夹卷过程特征,并通过敏感性试验着重分析了在此情况之下的夹卷速度参数化问题,以及风切变的作用。模拟结果表明,初始覆盖逆温改变了夹卷层的结构特征,使得夹卷层结构参数明显增大,风切变使这一效应略有增强,以往关于夹卷速度的参数化方案不再适用。分析研究表明,在有覆盖逆温的情况下,夹卷层结构参数是控制夹卷速度的关键因子,应该将夹卷层结构参数作为变量引入夹卷速度参数化方案,该方案能够很好地预报出受覆盖逆温影响的对流边界层的发展过程。

In this study,large-eddy simulation（LES） is employed to investigate the impact of capping inversion on the development of convective boundary layer（CBL）.The simulation results show that the structure of entrainment zone is significantly changed by the initial capping inversion.The stronger the initial capping inversion is,the larger the structure parameter β is.And this effect is slightly enhanced by the wind shear.The previous parameterization schemes for the entrainment rate can not describe the development of CBL satisfactorily.Analyses indicate that in this situation the development of CBL is controlled by the structure parameter of entrainment zone,and this factor should be included in the parameterization for the entrainment rate.The improved parameterization scheme is used to predict the CBL heights,and its validity is verified by the LES data.The results show that the new parameterization scheme can predict the development of CBL with capping inversion layer at the top.