Role of Mixed‐Layer Instabilities in the Seasonal Evolution of Eddy Kinetic Energy Spectra in a Global Submesoscale Permitting Simulation

Abstract

AbstractA submesoscale‐permitting global ocean simulation is used to study the upper ocean turbulence in high kinetic energy (KE) regions. Submesoscale processes peak in winter so that the geostrophic KE spectra tend to be relatively shallow in winter () with steeper spectra in summer (). This transition in KE spectral scaling has two phases. In the first phase (late autumn), KE spectra show the presence of two spectral regimes: power‐law in mesoscales and power‐law in submesoscales. The first phase appears with the onset of mixed‐layer instabilities, which convert available potential energy into KE, and this process results in a flattening of KE spectra at submesoscales. However, KE spectra at longer wavelengths follow scaling associated with a forward enstrophy transfer. In the second phase (late winter), KE produced through mixed‐layer instabilities is transferred to larger scales, and power‐law also develops in mesoscales.