WHOI PO

Title: Assessing submesoscale sea surface height signals from the SWOT mission

Abstract:

The Surface Water and Ocean Topography mission, launched in December 2022, maps out the elevation of the sea surface at a greatly improved precision. We here analyze the data that the wide-swath altimeter collected during the one-day repeat phase of the mission. We estimate along-track wavenumber spectra of sea surface height variance for the global ocean. In regions with an energetic mesoscale eddy field, the spectra have a mesoscale plateau, a steep drop-off due to balanced submesoscale turbulence, and a much flatter power-law tail at small scales. We characterize these spectra by fitting a spectral model. For the balanced signal, this fit yields a power-law exponent between −4 and −6 for most regions, broadly consistent with expectations and previous observations. The amplitude of the distinct small-scale signal, which typically dominates at wavelengths less than 30 to 50 km, is strongly correlated in time and space with the height of surface gravity waves, suggesting aliased wave signals as the most likely source. We propose a simple method to isolate the balanced signal in regions with negligible internal tides. Maps of the balanced signal in the Antarctic Circumpolar Current show compact cyclones with geostrophic relative vorticities frequently in excess of the local planetary vorticity, challenging the quasi-geostrophic framework commonly used to interpret altimetric data.