Thermohaline interleaving is an important mechanism for the lateral mixing of water masses in virtually every ocean basin. Horizontal diffusivities due to interleaving are often comparable with those due to mesoscale eddies, Theoretical research into thermohaline interleaving faces two important obstacles: (1) the need to accurately parameterize microscale mixing processes, including salt fingering, diffusive convection, convective overturning and shear-driven turbulence, and (2) the mathematical challenge of including baroclinic effects in linear and nonlinear theories. In this project, a coordinated sequence of linear and nonlinear theoretical analyses will address both of these problems. The linear stability analysis will delimit the parameter range in which oblique modes can be ignored. Preliminary results indicate that this range covers essentially all ocean regimes except near boundaries. The one-dimensional nonlinear modeling of cross-front modes will extend to the final equilibrium state. The direct numerical simulations will extend these results into the regime of three-dimensional nonlinear interleaving. At every stage, results will be compared with existing observational data.
Broader impacts The proposed research is a significant step toward the development of parameterizations of frontal exchange due to thermohaline interleaving in basin and global-scale models. It will also provide a test bed for mixing parameterizations that can be used in a wider class of models. A graduate student will receive training in state of the art theoretical and numerical techniques and an international collaboration will be fostered.
