Balanced and unbalanced contributions to dynamically-inferred sea surface height data in the St. Lawrence estuary

Abstract:

The future Surface Water Ocean Topography (SWOT) wide-swath satellite altimeter is expected to provide mapped Sea Surface Height (SSH) observations with an effective resolution of ~15 km. This should allow characterizing the balanced ocean surface circulation down to the largest submesoscales. However, SSH observations are contaminated by unbalanced internal wave signals with spatial scales similar to those of the balanced processes, and the poor temporal resolution of SWOT will not allow to separate the balanced and unbalanced signals in the time domain. At present, and until the planned 2021 launch of SWOT, there is no practical way of obtaining direct SSH observations at submesoscale resolution. However, dynamically-inferred SSH can be obtained from High-Frequency Radar (HFR) measurements of surface currents. Seven years of hourly HFR data are available in the St. Lawrence Estuary, with a horizontal resolution of 2 km. This region features both strong internal tides and mesoscale and submesoscale variability. These HFR data are used to characterize the contribution of balanced and unbalanced processes to the spatial and temporal variations of SSH in the St. Lawrence Estuary.