Marie-Pascale Lelong, Gerardo Hernandez-Dueñas, Leslie M. Smith

Submesoscale lateral transport of a passive tracer and Lagrangian particles in the ocean is investigated by means of numerical simulations with intermediate models. Using a projection technique, the models are formulated in terms of wave-mode and vortical-mode nonlinear interactions, and they range in complexity from full Boussinesq to waves-only and vortical-modes-only models. We find that, on these scales, most of the dispersion is done by vortical motions, but waves cannot be discounted because they play an important, albeit indirect, role. In particular, we show that waves are instrumental in filling out the spectra of vortical-mode energy at smaller scales through vortex-wave-wave triad interactions. Waves also transfer energy upscale to Vertically Sheared Horizontal Flows (VSHF) which are a key ingredient for internal-wave shear dispersion. We demonstrate that a richer spectrum of vortical modes in the presence of waves enhances the effective lateral diffusivity, compared to QG. In the waves-only model, the dispersion rate is an order of magnitude smaller and is attributed entirely to internal-wave shear dispersion. Some shear dispersion is also present in the Boussinesq model, but notably absent when wave-triad interactions are not included.