Toward a method to estimate geostrophic transport from along-track coastal altimetry on shelf and shelf-break regions
Event: 2020 Ocean Surface Topography Science Team Meeting (virtual)
Session: Coastal Altimetry
Presentation type: Type Forum
Since 2009, the Meridional Overturning Circulation (MOC) in the South Atlantic has been observed with an array of in situ moorings on each side of the basin at 34.5°S, the South Atlantic MOC Basin-wide Array (SAMBA). To date, the meridional transport inshore of the shallowest SAMBA moorings (inshore of the 1300 m isobaths) on either side of the basin has been estimated using a time-mean from an ocean model simulation, due to lack of better observations. However, because the nearest shore moorings are offshore of the shelf break, the portion of the transport that is not directly observed is significant and represents 3 to 4 Sv out of the ~18 Sv total MOC transport at 34.5°S, i.e. ~20%. We aim to use along-track coastal altimetry, combined with existing in situ data, to estimate the inshore component of the transport at 34.5S unobserved by the SAMBA array, and so refine the MOC estimates. This requires designing a method to estimate the geostrophic transport based on surface altimetry data. Such a method necessitates estimating both the barotropic and baroclinic components of the flow. We present here an initial analysis of the vertical ocean structure on the South American side of the SAMBA array, using available in situ observations. At the location of the most inshore Pressure-equipped Inverted Echo Sounder (PIES) mooring of the SAMBA array, located on the ~1300 m isobath, the sea level variability is largely dominated by baroclinic variability. Further inshore, on the ~400 m isobath, data from a moored Acoustic Doppler Current Profiler (ADCP) show that the barotropic component is dominant. On the shelf itself, lowered ADCP data collected during various research cruises suggest a large variability in the current structure. These various data sets will allow us to estimate the vertical structure of the flow across different regimes on the shelf and the shelf break, which we will use to derive our method to estimate the altimetry-derived geostrophic currents and determine the associated transports.