41 The Influence of an Eddy-Diffusivity/Mass-Flux (EDMF) Turbulence Parameterization on Convective Self-Aggregation

Monday, 26 June 2017
Salon A-E (Marriott Portland Downtown Waterfront)
Wolfgang Langhans, LBNL, Berkeley, CA; and W. D. Collins

The existence of self-aggregation of convection in convection-permitting simulations of radiative-convective equilibrium has received lots of attention in recent years. The climate of the aggregated state is overall drier and permits increased outgoing longwave radiation. The initiation of this state has been explained by a variety of diabatic feedbacks that increase the spatial variance of column-integrated moist static energy (MSE). Others deemed low clouds and their cloud-radiative forcing responsible for the initiation of a low-level circulation that supports aggregated convection by carrying more MSE into the convecting column.

However, these simulations are typically carried out on grids too coarse (dx~3 km) to resolve shallow clouds and boundary layer turbulence. Adding to this uncertainty, several studies do not find aggregated states in higher-resolution simulations. This motivates us to run simulations in which boundary-layer turbulence and clouds are parameterized following an Eddy-Diffusivity/Mass-Flux (EDMF) approach. We find that RCE over a sea surface temperature of 305 K aggregates without EDMF, but does not aggregate with EDMF included. By modifying the parameterized boundary-layer processes we study and discuss the physics that prevent from aggregation.

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