S-2DV: A New Reduced Model Generating Submesoscale-Like Flows

Oceanic mesoscale flows are characterized by an inverse kinetic energy cascade and the subsequent formation of large coherent vortices, and these flow features are captured well by the quasi-geostrophic (QG) model. Oceanic submesoscale flow dynamics are however significantly different from those of mesoscales. The increase in unbalanced energy levels and the Rossby number at submesoscales results in cyclone-anticyclone asymmetry in vorticity structures, forward kinetic energy cascades, and enhanced small-scale dissipation. In this paper, we develop a reduced single-equation model that can generate submesoscale-like flows in two dimensions. We start from the two-dimensional barotropic QG equation and add an external random vorticity field, to mimic the effect of unbalanced flow components. Thereafter, we add a vorticity-squared term, to generate asymmetry in the vorticity structures. By varying the strength of these two terms, we observe that the model can generate submesoscale-like flows that compare qualitatively well with realistic flows generated by complex ocean models. The reduced model is seen to be capable of generating flows that are intermittent in nature, are characterized by a forward energy flux, and are composed of small-scale flow structures along with enhanced energy dissipation. We further demonstrate the practical utility of the model by applying it to a passive tracer dispersion and a plankton patchiness problem, these being applications that require submesoscale-like flows. Our investigation points out that the new model could serve as a convenient platform for various applications that require submesoscale-like flows, such as testing and developing different kinds of parameterizations.