WHOI PO

Title: Balanced ocean submesoscale motions beyond geostrophy: mathematical modelling in the context of SWOT

Abstract: At the ocean submesoscale, inertial gravity waves (IGW) and "balanced" motions co-exist at the same spatial and temporal scales. Separating them in model and observational data is an important task as part of the effort of understanding the energetics and transport properties of each type of motion. This is challenging in the submesoscale, where no agreed-upon definition of what a balanced motion is. Order one Rossby number features like submesoscale vortices and fronts escape the description of the QG model. In this direction, my Ph.D. work has been dedicated to the study of QG+1, a balanced model extending QG to the next order in Rossby number. It is by definition free of IGW. Through simulation of submesoscale turbulence using QG+1, we show that QG+1 can capture the turbulent statistics of the ocean submesoscale balanced motion, beyond the capabilities of QG. QG+1 description of a strain-induced front blows up in finite time, recovering this qualitative feature of the semigeostrophic model. QG+1 has the promise to be a potent skeleton model for the reconstruction of submesoscale velocity from SWOT SSH data, since its diagnostic relations include the omega-equation and cyclogrostrophic balance.