A Mean-Gradient Model of the Dry Convective Boundary Layer

Abstract

A mean-gradient model of the dry convective boundary layer is developed using a convective mass flux representation of the turbulent fluxes. A top-hat model of thermals is used to represent the average characteristics of updrafts and downdrafts in the buoyantly driven circulation. The convective mass flux is related to the convective velocity scale. Although the model is computationally simple, it describes the basic structure of the CBL. In this parameterization the vertical gradients of conserved variables are controlled by internal mixing through vertical mass transports inside the convective boundary layer, bottom mixing due to the surface processes, top mixing due to the entrainment, and lateral mixing between updrafts and downdrafts.