Mean surface topography of the northwest Atlantic: Comparison of estimates based on satellite, terrestrial gravity, and oceanographic observations

Abstract

The accuracy of a new mean sea surface topography (MSST) of the northwest Atlantic is assessed. The MSST is estimated from 12 years of altimeter observations referenced with respect to a new regional geoid based on a blend of Gravity Recovery and Climate Experiment (GRACE), terrestrial, and altimeter-derived gravity data. The new MSST is first compared to a recently published mean surface topography calculated using an eddy-permitting model of the North Atlantic. Geostropic currents calculated from the GRACE-based MSST are next compared to mean surface currents in the northwest Atlantic estimated from the motion of near-surface drifters corrected for surface Ekman effects. Finally, the mean path of the Gulf Stream is compared to the line of zero skewness of sea level variability which provides a measure of the mean path of unstable, intense ocean currents. Overall the agreement amongst the various estimates of surface topography and circulation is excellent. There are, however, some significant differences that can be separately attributed to problems with the MSST and, in some cases, with the ocean model (in particular the ocean climatology to which it was nudged).