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

Abstract

A new one‐dimensional (1‐D) parameterization of penetrative convection has been developed in order to have a better representation of the vertical mixing in ocean general circulation models. Our approach is inspired from atmospheric parameterizations of shallow convection which assumes that in the convective boundary layer, the subgrid‐scale fluxes result from two different mixing scales: small eddies, which are represented by an Eddy‐Diffusivity (ED) contribution, and large eddies associated with thermals, which are represented by a mass‐flux contribution. In the present work, the local (small eddies) and nonlocal (large eddies) contributions are unified into an Eddy‐Diffusivity‐Mass‐Flux (EDMF) parameterization which treats simultaneously the whole vertical mixing. EDMF is implemented in the community ocean model NEMO and tested in its 1‐D column version. Deepening of dense water in analytic cases, successfully reproduced in LES simulations, is more realistic with EDMF than with standard diffusion parameterizations. Also the convective events observed in the western Mediterranean at the Lion station and in the North Pacific Ocean at the PAPA station are more realistic in terms of sequencing and amplitude with EDMF.

Wind-Forced Submesoscale Symmetric Instability around Deep Convection in the Northwestern Mediterranean Sea

“…During the study period, satellite images showed a maximum deep convection area of 15,800-24,100 km 2 in winter 2011 [1] compared in the model to a maximum area where the MLD exceeded 500 m of 9100 km 2 reached on 24 January. This is satisfactory for our study of frontal processes in the presence of deep mixed layer, but illustrates the difficulty to represent deep convection in regional and global numerical models and the importance of convection parameterization (see for instance [108]).…”

A new stochastic ocean physics package and its application to hybrid‐covariance data assimilation

“…However, also in the ocean, deep convective plumes occur at sub-grid (sub-kilometric) scales and have significant effects on large-scale thermohaline circulation (Paluszkiewicz et al, 1994). Thus, ocean parametrizations have been proposed in analogy to the atmospheric ones (Paluszkiewicz and Romea, 1997); convective plumes can likewise affect the subgrid-scale kinetic energy budget (Campin et al, 2011;Ilicak et al, 2014, Giordani et al, 2020, and are therefore accounted for in the present SKEB scheme.…”

“…However, also in the ocean, deep convective plumes occur at sub‐grid (sub‐kilometric) scales and have significant effects on large‐scale thermohaline circulation (Paluszkiewicz et al ., 1994). Thus, ocean parametrizations have been proposed in analogy to the atmospheric ones (Paluszkiewicz and Romea, 1997); convective plumes can likewise affect the subgrid‐scale kinetic energy budget (Campin et al ., 2011; Ilicak et al ., 2014, Giordani et al ., 2020), and are therefore accounted for in the present SKEB scheme. Here, for any grid point in the tri‐dimensional model grid, the convection dissipation energy is approximated by: where k c is a resolution‐dependent parameter that quantifies the convection activity (in m·s −1 ), M k is the mass flux across the k th vertical level, and dz and ρ 0 are the vertical level thickness and reference density, respectively.…”

An Improved Perturbation Pressure Closure for Eddy-Diffusivity Mass-Flux Schemes

“…where c div = 0.4 is a scaling coefficient, andẼ ij and∆ ij are the entrainment and detrainment rates proposed by Cohen et al (2020). The second term is an addition for the bubble test case only; it has been implemented in an EDMF scheme for simulating oceanic convection (Giordani et al, 2020) and a multi-fluid framework for the thermal bubble (Weller et al, 2020). The bubble test case is an initial value problem that is different from the typical boundary value problems for turbulence and convection that a SGS model needs to simulate in a climate model, and hence the introduction of these additional terms, not present in Cohen et al (2020) and Lopez-Gomez et al (2020), may be justified.…”