Similarity of Scalar Fields in the Convective Boundary Layer

Abstract

The paper investigates similarity of scalar fields in a horizontally homogeneous, cloud-free, shearless, convective mixed layer. The concept of the ?bottom-up? and ?top-down? decomposition is verified for both passive and active scalars, based on a number of large eddy simulations. The bottom-up diffusion is not confirmed to be countergradient. The top-down scaling, based on the values of entrainment fluxes, is found to be inefficient. Alternative sets of scales are proposed and validated for mean values of scalars. For the bottom-up process, the?free-convective? scaling is applied. For the top-down processes, new scales are based on the maximum values of scalar gradients in the interfacial layer. The bottom-up and top-down similarity functions for passive and active scalars are found equal.