Computing vertical mixing from Swot sea surface heights

Large mesoscale eddies (100–300 km) have a critical role in the horizontal transport of heat, salt, carbon, nutrients and biomass in the ocean, and contribute to the vertical mixing, driving global upward vertical transport.
Small mesoscale and submesoscale features, smaller than 100 km and composed by eddies, filaments and fronts, drive strong vertical velocities, up to one order of magnitude higher than at the mesoscales, extending well below the mixed layer.  However, direct measurement of vertical mixing is challenging, and generally in-situ observations are limited in space and time. Satellite altimeters observe the surface ocean topography, and traditionally cannot resolve these small scales.Swot brings a whole new capability of observing small ocean structures of 5–10 km with a time coverage of the order of a few days - or better at high latitudes.

A recent work has focused on the Southern Ocean region south of Tasmania, across the Polar Front. The area has strong water mass variations across the Polar front, energetic mesoscale   dynamics, while, due to the east-west flow direction of the Antarctic Circumpolar Current, no strong north-south mean current carry heat poleward in the upper 2,000 m.
Instead, heat fluxes are carried by mesoscale eddies across the Antarctic Circumpolar Current, thus making their knowledge crucial for the understanding of transport in the area.
Here, Swot surface observations have been used to reconstruct the vertical dynamics using an effective Surface Quasi Geostrophy (eSQG) methodology. Estimating the vertical velocities under Swot tracks gives promising results. Effective Surface Quasi Geostrophy methodology is able to estimate the majority or the vertical velocities’ amplitude (up to 70-90% depending on the depth) at scales down to 30-70 km depending on the depth.

This should provide us with realistic estimates of the vertical mixing in the region, and thus better estimates of heat and nutrient transports.