A Simplified Higher Order Closure + Mass Flux Boundary-Layer Parameterization in the Goddard Earth Observing System

Abstract

Boundary-layer turbulence and clouds play an essential role in regulating surface fluxes and the Earth's radiative balance, but their parameterization in global models remains a significant source of uncertainty. This paper describes a novel implementation of the Simplified Higher Order Closure (SHOC) coupled with a multi-plume eddy diffusivity mass flux scheme in the NASA Goddard Earth Observing System (GEOS) model. The SHOC scheme provides eddy diffusivities and uses a set of higher order moments (HOMs) to constrain an analytic double Gaussian probability distribution function (PDF), from which the subgrid buoyancy flux and cloud properties are diagnosed. This SHOC + MF implementation extends previous work by including mass flux contributions to all HOMs, which remedies a significant underestimation of subgrid scale variances, and allows the combined convective and stratiform cloud properties to be diagnosed from the assumed PDF in a unified way. Single column experiments show the SHOC + MF scheme compares favorably to large eddy simulations in trade cumulus, marine stratocumulus, and continental convective boundary-layer regimes, relative to the default GEOS boundary-layer parameterizations. Global experiments show improvements in simulated clouds and surface stress. This study demonstrates the feasibility of a closer coupling between higher order closure and MF, and a unified representation of shallow clouds.