Submesoscale dynamics in the Bay of Bengal: Inversions and instabilities

High-resolution observations reveal the complex processes controlling the evolution and subduction of a cold and salty, dense filament in the Bay of Bengal. The filament, likely formed through coastal upwelling, was advected offshore by a mesoscale strain field and brought adjacent to fresher water from runoff and rain. The front on an edge of the dense filament is observed to undergo restratification and steepening, responding to evolving mesoscale and submesoscale convergence and divergences. Measurements and analyses indicate the development of both small-scale instabilities (such as SI) and slightly larger-scale ageostrophic secondary circulation, acting in concert to subduct and stir surface heat into the interior. Our results highlight the importance of small-scale three-dimensional dynamics in setting upper ocean properties in the Bay of Bengal.