Abstract
We demonstrate that an extended eddy‐diffusivity mass‐flux (EDMF) scheme can be used as a unified parameterization of subgrid‐scale turbulence and convection across a range of dynamical regimes, from dry convective boundary layers, through shallow convection, to deep convection. Central to achieving this unified representation of subgrid‐scale motions are entrainment and detrainment closures. We model entrainment and detrainment rates as a combination of turbulent and dynamical processes. Turbulent entrainment/detrainment is represented as downgradient diffusion between plumes and their environment. Dynamical entrainment/detrainment is proportional to a ratio of a relative buoyancy of a plume and a vertical velocity scale, that is modulated by heuristic nondimensional functions which represent their relative magnitudes and the enhanced detrainment due to evaporation from clouds in drier environment. We first evaluate the closures off‐line against entrainment and detrainment rates diagnosed from large eddy simulations (LESs) in which tracers are used to identify plumes, their turbulent environment, and mass and tracer exchanges between them. The LES are of canonical test cases of a dry convective boundary layer, shallow convection, and deep convection, thus spanning a broad rangeof regimes. We then compare the LES with the full EDMF scheme, including the new closures, in a single‐column model (SCM). The results show good agreement between the SCM and LES in quantities that are key for climate models, including thermodynamic profiles, cloud liquid water profiles, and profiles of higher moments of turbulent statistics. The SCM also captures well the diurnal cycle of convection and the onset of precipitation.
Highlights
Turbulence and convection play an important role in the climate system
We demonstrate that an extended eddy‐diffusivity mass‐flux (EDMF) scheme can be used as a unified parameterization of subgrid‐scale turbulence and convection across a range of dynamical regimes, from dry convective boundary layers, through shallow convection, to deep convection
Our goal in this paper is to develop a unified set of closures that work across the range of turbulent and convective motions, within one specific type of parameterization scheme known as an eddy‐diffusivity mass‐flux (EDMF) scheme (Siebesma & Teixeira, 2000; Siebesma et al, 2007; Wu et al, 2020)
Summary
Turbulence and convection play an important role in the climate system They transport energy, moisture, and momentum vertically, thereby controlling the formation of clouds and, especially in the tropics, the thermal stratification of the atmosphere. They occur on a wide range of scales, from motions on scales of meters to tens of meters in stable boundary layers and near the trade inversion, to motions on scales of kilometers in deep convection. General circulation models (GCMs), with horizontal resolutions approaching tens of kilometers, are unable to resolve this spectrum of motions. Journal of Advances in Modeling Earth Systems motions, on scales of kilometers to tens of kilometers, are beginning to be resolved in short‐term global simulations (Kajikawa et al, 2016; Stevens et al, 2019)
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