An energetically and observationally constrained mesoscale parameterization for ocean climate models

An extension of the GEOMETRIC parameterization (Mak, Marshall, et al., 2022, https://doi.org/10.1029/2022ms003223) for the mesoscale eddy transport is proposed and tested in a one-degree resolution global ocean model. It consists in solving a prognostic two-dimensional equation for the eddy kinetic energy (EKE). The parameterized EKE budget is calibrated from an observation-based estimate of the EKE reservoir, allowing an unprecedented realism of the subgrid EKE field within a global eddy-parameterizing ocean configuration. The predicted EKE map is then used to specify temporal and spatial variability of both the Gent-McWilliams coefficient (Kgm) and the neutral diffusivity of tracers (Kgm) which display strong horizontal variations and a general decrease in polar regions. Using a suite of hindcast ocean simulations, we assess the respective effects of the novel distributions of Kgm and Kn. Changes in Kgm impact strongly the simulated global ocean circulation: they increase the eastward volume transport through Drake Passage by 21 Sv and the Atlantic Meridional Overturning Circulation strength at 26°N by 2.6 Sv, reducing biases. Changes in Kn can substantially modify the transfer of surface water properties into the ocean interior: we find a strong influence on sea surface temperatures and ocean heat storage. The results highlight the need to physically constrain mesoscale transport in ocean climate models. By linking the two eddy coefficients to the same subgrid EKE, itself constrained from indirect observations of EKE, our developments represent a significant advancement toward unified and energy-consistent mesoscale parameterizations.