稳定大气边界层结构演变的数值研究

NUMERICAL STUDY ON THE EVOLUTION OF THE STABLE BOUNDARY LAYER

本文应用二阶矩闭合模式研究了在不同的下垫面降温情况下稳定大气边界层结构的演变过程。结果表明:下垫面降温不同,稳定大气边界层内平均位温廓线的演变规律也不同,风廓线和脉动量廓线也相应地变化。影响温度廓线演变的因子除了湍流扩散作用以外,还有由于湍流交换作用在垂直方向的非均匀分布而产生的类似垂直平流作用的输送项。若下垫面经过一段时间的明显降温后降温停止或很少,则这种输送作用能改变位温廓线斜率在垂直方向上的分布规律。即由斜率在垂直方向的单调变化演变为非单调变化。

In this paper, the atomspheric boundary lyaer model with the second-order momen closure has been developed to study the evolution of the stable boundary layer with different surface de tempera ture sates, it is found that (1) When surface de tempera ture rates is larger, in the stable boundary layer the height is lower where the temperature is forced to decrease by the earth surface, the supergeostrophic wind is larger, the height of the maxium supergeo-strophic wind is lower, correspondly the turbulent fluctuation energy and the turbulent exchange coefficient become smaller, and the turbulent heat flux becomes larger. (2) After the surface detemperaure rate is small or even zero, the slopes of the temperature profile ard velocity Profile in the stable buondary layer becomes non-monotonous change from original monotonous change, accordingly the slope of turbulent fluctuation energy profile and the hea tflux profile also appear the simila change. The phenomenon is analysed theoroticaly and it is suggested that the vertical non-uniform distribution of the turbulent exchange is a main factor which result in the nonmomotonous change of the slopes. There is upward transport similar to the vertical advection above the intense turbulent mixture and downward transport below. these transports made the slopes of the mean variation profiles change non-monotonously.