Multiscale modeling of vertical and horizontal dispersion of material by submesoscale motions in frontal regions

Sutanu Sarkar

Vertical transport from surface to depth in the upper ocean presents a challenge to both measurement and and prediction because of its small magnitude, its spatiotemporal intermittency and its uncertain links to environmental forcing. Recent and ongoing work points to the importance of coherent eddy-driven flow convergences in mediating vertical transport. The vorticity and strain increase as the length scale of the eddying motion decreases towards the submesoscale but the time scale over which the flow field remains coherent also changes with decreasing length scale in a manner that is poorly understood. We propose numerical simulations of frontal regions that are seeded with an ensemble of floats to study the space-time behavior of submesoscale eddies. High spatial resolution of O(m) will be employed in all directions to capture the multiscale nature of submesoscale vortices (the hotspots of coherent vertical transport) as well as filaments with high turbulent dissipation rate. The associated horizontal and vertical dispersion of floats will be obtained in idealized simulations of baroclinic instability as a function of frontal strength, stratification and wind forcing. Supplementary simulations steered by observations of fronts in the proposed DRI site (western Mediterranean) will be conducted. Lagrangian particles will be compared with floats that deviate from truly Lagrangian tracking owing to inertia and buoyancy. The simulation results will be analyzed using Lagrangian statistics, multiscale diagnostics and, in collaboration with other DRI investigators, also tools of Lagrangian chaos theory.