Modeling stratocumulus-topped boundary-layer structure with statistical diffusion theory

Proper parameterization of vertical turbulent fluxes is of fundamental importance in numerical simulation of the atmospheric flow because surface-atmosphere exchanges are mainly associated with turbulent mixing. In this study, a parameterization for the eddy diffusivity coefficient is used in a single column model (SCM) to simulate the stratocumulus-topped boundary-layer (STBL). The scheme is suitable when a fine resolution is used in the vertical, along with a coarse resolution in the horizontal that does not allow the boundary-layer structure to be explicitly resolved (as in mesoscale and large-scale models). The parameterization is obtained by fitting turbulence data collected during the 2nd Aerosol Characterization Experiment (ACE-2). Mixing length-based analytical equations are obtained based on Taylor's statistical theory of turbulence. Single-column model simulations of two ACE-2 diurnal cases and a nocturnal ASTEX case show good agreement between model results and observations in both coupled and decoupled situations. A noticeable characteristic of the turbulence scheme, since it uses a first-order closure, is its low computational cost. (c) 2005 Elsevier B.V. All rights reserved.