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.