层积云覆盖的边界层数值模拟研究 (Ⅰ):数值模式的建立

A Numerical Study on the Stratocumulus-ToppedPlanetary Boundary Layer Part (I): Model Development

层积云是一种在湍流作用下形成的边界层云。在这种边界层中 ,层积云顶即边界层顶、云层和非云层耦合在一起。为了加深对这种层积云覆盖的边界层的理解 ,许多作者已经做了大量的野外观测和数值试验研究。然而在数值模拟研究中存在湍流和云物理模式相互脱节的现象。针对这种缺陷 ,本文在湍流控制方程组中引入云滴控制方程 ,发展了一个新的用于研究海区层积云覆盖的边界层的数值模式。所建模式具有如下特点 :(1)实现了云物理模式与湍流模式的相互耦合 ;(2 )实现了云滴分档凝结模式和三阶湍流闭合边界层模式相互耦合。利用所建模式对大涡模拟对比试验所采用的个例进行了数值模拟。数值模拟结果表明 ,该边界层模式能较合理地模拟海区层积云覆盖的边界层微湍流结构和云微物理过程。

Stratocumulus is a kind cloud formed by turbulent force in boundary layer. The cloud top is the boundary layer top, so it is called stratocumulus-topped boundary layer. The cloud layer and cloudless layer coupled in this kind boundary layer. For understanding the stratocumulus-topped boundary layer, a numbers of field observation and numerical simulation have been made. But, there is a fatal defect in some coupled model, that is the turbulent model and cloud physical model do not coupled properly. For overcoming this problem, anew numerical model of the cloud-topped planetary boundary layer is developed by using cloud drop equation in the turbulent equations. The model is one-dimensional with special emphasis on a detailed description of cloud microphysical processes. (1) The interaction between turbulent and cloud microphysics is considered. (2) The model has third-order turbulenceclosure planetary boundary layer model coupled with size-resolved cloud microphysical model. The simulation made by the new model on the case which was proposed by C. -H. Moeng in 'the stratocumulus-topped planetary-boundary layer: Intercomparison among different numerical codes' is presented and compared with some observations and some simulations. The result shows that the new model can simulate the turbulent structure and the cloud microphysical processes of the marine stratocumulus-topped planetary boundary layer.