First global assessment of the Eddy-Diffusivity Mass-Flux (EDMF) parameterization for oceanic convection in NEMO: implications for global temperature and surface heat fluxes

Abstract. The Eddy-Diffusivity Mass-Flux (EDMF) parameterization provides a unified framework to represent both local (diffusive) and non-local (convective) vertical mixing in the ocean. While EDMF has been evaluated in idealized and regional configurations, its performance in global ocean models has not yet been assessed. We present the first global-scale evaluation of the EDMF scheme implemented in NEMO and compare it with the widely used Enhanced Vertical Diffusion (EVD) and Mixed Layer Penetration (MLP) parameterizations. Three global 1/4° simulations for 1999–2020 are analyzed, focusing on convective regimes, upper-ocean temperature and mixed-layer depth.

EDMF successfully reproduces both shallow diurnal convection in the tropics and deep wintertime convection in subpolar regions, with modelled plume timing, penetration depth and vertical velocities consistent with available observations. In the tropics, EDMF captures the observed penetrative cooling and depth variability of nocturnal cold plumes, in contrast to the instantaneous adjustment produced by EVD. In deep-convection regions such as the Labrador Sea, EDMF simulates realistic interannual variability in convective depth and intensity.

The improved representation of convective regimes leads to a ~30 % reduction in global upper-ocean (0–700 m) temperature biases in EDMF compared to EVD-based simulations. Changes in latent heat loss, driven by SST differences, dominate the associated changes in net surface heat flux between EDMF and EVD simulations, corresponding to ~6.5 % of the global average net climatological surface heat balance.

These findings demonstrate that EDMF provides a more physically consistent representation of oceanic convection and offers an alternative to traditional and empirical EVD- and MLP- based approaches.