A Unified Eddy-Diffusivity/Mass-Flux Approach for Modeling Atmospheric Convection

Abstract

A fully unified parameterization of boundary layer and moist convection (shallow and deep) is presented. The new parameterization is based on the stochastic multiplume eddy-diffusivity/mass-flux (EDMF) approach, which distinguishes between convective plumes and nonconvective mixing. The convective plumes represent both surface-forced updrafts and evaporatively driven downdrafts. The type of convection (i.e., dry, shallow, or deep) represented by the updrafts is not defined a priori, but rather depends on the near-surface updraft properties and the stochastic interactions between the plumes and the environment through lateral entrainment. Consequently, some updrafts may contribute only to the nonlocal transport within the subcloud layer, while others may condense and form shallow or even deep convection. Such a formulation is void of trigger functions and additional closures typical of modular parameterizations. The updrafts are coupled to relatively simple warm-, mixed-, and ice-phase microphysics. Each precipitating updraft forms a downdraft driven by the evaporation of detrained precipitation. The downdrafts control the development of cold pools near the surface that can invigorate convection. The new parameterization is tested in a single-column model against large-eddy simulations (LESs) for cases representing weakly precipitating marine convection and the diurnal cycle of continental deep convection. The results of these EDMF experiments compare well with the LES reference simulations. In particular, the transitions between the different dominant convection regimes are realistically simulated.

Towards Unifying the Planetary Boundary Layer and Shallow Convection in CAM5 with the Eddy-Diffusivity/Mass-Flux Approach

“…Another important aspect worth exploring is the numerical performance of the scheme and its optimal coupling with the CAM's framework. In the long term, the EDMF scheme is meant to include the deep convection parameterization, as discussed in [38,39], with a potential scale adaptivity for the mass-flux (cf. [40]) and eddy-diffusivity (cf.…”

On the Parameterization of Convective Downdrafts for Marine Stratocumulus Clouds

“…The idea behind EDMF is to parameterize the turbulent fluxes as a sum of local (diffusive) transport through ED and nonlocal (convective) transport through the mass-flux contribution. The EDMF approach has been extended to represent moist convection since then (e.g., Soares et al 2004;Neggers et al 2009;Neggers 2009;Angevine et al 2010Angevine et al , 2018Su selj et al 2013;Suselj et al 2019a,b). For the moist extention, the updrafts start out as dry and condense when the saturation conditions are met.…”

“…where a w 5 1, b w 5 1.5 are model constants (de Roode et al 2012;Su selj et al 2013;Suselj et al 2019b). Variable B un 5 g(u y,un /u y 2 1) is the updraft buoyancy, and u y 5 u(1 1 0:61q y 2 q l ) is the virtual potential temperature.…”

An Eddy‐Diffusivity Mass‐Flux Parameterization for Modeling Oceanic Convection

“… w e is related to the plume and large scale vertical velocities by the mass‐conservation equation in a grid‐cell which writes as: where is the resolved large scale vertical velocity which results from the continuity equation in a three‐dimensional model. As shown by Suselj et al (2019), the mass flux defined as is commonly approximated by F M = a p w p because of usually small fractional convection area ( a p ≤ 0.1) and small resolved vertical velocity (≃10 −5 m s −1 ) compared to the convective velocity w p (≃10 −2 m s −1 ).…”