夹卷层厚度定义对其参数化的影响

On the definition and parameterization of the entrainment zone depth at the top of convective boundary layer

关于边界层顶部夹卷层厚度的参数化,通常采用的方案是建立无量纲夹卷层厚度与对流理查森数之间的指数对应关系.以往的研究结果显示,幂指数存在很大的不确定性,至今尚无定论.基于对流边界层的垂直结构模型(即一阶模型),本文分析了"热泡理论"和"能量平衡理论"在物理模型上的差异,及其对夹卷层厚度参数化方案的影响,并用大涡模拟数据进行了验证.结果表明,"热泡理论"对应的夹卷层厚度与"能量平衡理论"对应的夹卷层厚度不同;前者的夹卷层厚度应该满足对流理查森数的-1次律,而后者的夹卷层厚度应该满足对流理查森数的-1/2次律.

As for the parameterization of the entrainment zone depth at the top of the convective boundary layer, the commonly-used scheme is to establish the relationship between the dimensionless entrainment zone depth and a power law of the convective Richardson number. The previous studies show that there exists a large uncertainty about the value of the exponent. Based on the bulk model of convective boundary layer, the first-order jump model, the difference between the parcel theory and the energy balance model, which will lead to different power laws, is discussed in this paper. Analyses indicate that the definition of the entrainment zone depth in the parcel theory is different to that in the energy balance model, but the difference was not distinguished in the previous studies. Theoretical derivations suggest the dependence of the dimensionless entrainment zone depth on the convective Richardson number should be the -1 law in the parcel theory, while the -1/2 law in the energy balance model. These results are supported by the data from large-eddy simulations （LES）.