Presenter: Rosemary Morrow (LEGOS / OMP)

Description:
Gridded altimetric maps of sea surface height (SSH) and geostrophic currents have allowed significant progress in our understanding of ocean dynamics on spatial scales larger than 150 km in wavelength. The future SWOT mission will allow us to explore spatial scales down to 14-40 km in wavelength depending on the sea state conditions. Here we perform an analysis of horizontal geostrophic eddy diagnostics in the Agulhas Current region, to evaluate the contribution of these scales as observed with altimetry today (> 150 km) and potentially with SWOT (< 150 km). We use “pseudo” altimetric sea surface height fields based on a MITGCM SSH fields including realistic atmospheric and tidal forcing, that have been corrected for high-frequency motions of barotropic tides and the Dynamical Atmospheric Corrections. These corrected SSH fields are filtered temporally (at 48h to remove the residual high-frequencies) and spatially (to separate today’s observable scales > 150 km from the SWOT scales < 150 km). Geostrophic currents are then derived, and higher order eddy diagnostics of eddy kinetic energy, strain and barotropic eddy-mean energy transfers. These eddy diagnostics show the strong contribution of the finer scales in the Agulhas region. EKE, strain and eddy-mean transfers dominate at finer scales along the continental slope for the Agulhas Current, and within the core of the meandering current after the Retroflection. The fine-scale strain (<150 km) is a factor of 3 greater than the larger mesoscale strain (> 150 km) observed with altimetry today. The observability of these processes with SWOT is further explored with the SWOT ocean simulator, to evaluate the impact of spatio-temporal sampling and errors on these diagnostics, and to observe their detection in the Cape Cauldron region, where in-situ deployments are planned during the 1-day repeat CalVal phase of SWOT.