Parameterizing Submesoscale Vertical Buoyancy Flux by Simultaneously Considering Baroclinic Instability and Strain‐Induced Frontogenesis

Abstract

AbstractOceanic submesoscale processes (submesoscales) with O(1–10) km horizontal scale can generate strong vertical buoyancy flux (VBF) that significantly modulate upper‐ocean stratification. Because submesoscales cannot be resolved by the prevailing ocean models, their VBFs have to be properly parameterized in order to improve model performance. Here, based on theoretical scaling analysis, we propose a new parameterization of submesoscale VBF by simultaneously considering mixed‐layer baroclinic instability (MLI) and strain‐induced frontogenesis, which are two leading generation mechanisms of submesoscales that typically co‐occur in open ocean. Compared with the parameterization of Fox‐Kemper et al. (2008, https://doi.org/10.1175/2007jpo3792.1; F08) that only considers the MLI, the new parameterization includes mesoscale strain rate and improves vertical structure function. Diagnostic validations based on submesoscale permitting simulation outputs suggest that the newly parameterized VBFs are more realistic than F08 in regard to three‐dimension distributions. How to incorporate this new parameterization into coarser‐grid ocean models, however, needs further studies.