Properties of Small-Scale Langmuir Turbulence in the Presence of Submesoscale Eddies

Recent research has shown that there are important interactions between small-scale Langmuir turbulence and much larger submesoscale eddies in the oceanic mixed layer. Vertical mixing and transport by Langmuir turbulence competes with restratification by submesoscale eddies, thereby deepening the mixed layer, and the prevalence of symmetric instabilities in the development of upper-ocean eddies is reduced. Numerical simulations of the interactions between Langmuir turbulence and submesoscale eddies have further indicated that there are substantial effects on the small-scale properties of Langmuir cells in the presence of eddies generated during the spin-down of a large-scale temperature front. These simulations solve the Craik-Leibovich Boussinesq equations over a domain of size 20km with grid scale close to 5m, thereby allowing simultaneous resolution of both Langmuir turbulence and submesoscale eddies. Here we examine changes to the orientation, magnitude, dynamics, and other properties of Langmuir cells in the presence of temperature gradients generated by larger-scale eddies. The analysis is carried out, in part, through the calculation of conditional statistics at locations where temperature gradients are large and where the strongest effects on Langmuir cells are observed to occur. The dynamical budgets governing the evolution of vorticity and vortical Langmuir cells are examined at these interaction locations and dominant processes in the dynamics are identified. The coupling between the vorticity and temperature fields is also considered and connected to the observed small-scale flow features. An attempt is made to explain the observed features using a linearized rapid distortion analysis of the Langmuir cell evolution. Finally, directions for future research and the implications of these results for upper ocean structure, small-scale vertical transport and mixing, and ocean tracer evolution are outlined.