||The circulation of the North Atlantic Ocean from altimetry and the GRACE geoid
We discuss the ocean circulation derived from the temporal-averaged sea surface height, which is referenced to the recently released geoid (GGM02) from the Gravity Recovery And Climate Experiment (GRACE) mission. The creation of a precise, independent geoid allows for the calculation of the reference gravitational potential undulation surface, which is associated with the resting-ocean surface height. This reference height is then removed from the temporal-averaged sea surface height, leaving the dynamic ocean topography. At its most basic level, the dynamic ocean topography can be related to the ocean's surface circulation through geostrophy. This has previously been impracticable due to large uncertainties in previous estimates of the Earth's geoid. Prior geoids included the temporal-averaged sea surface from altimeters as a proxy for the geoid, and therefore were unsuitable for calculations of the ocean's circulation.
Geoid undulations are calculated from the GRACE geoid and compared to those from the EGM96 geoid. Error estimates are made to assess the accuracy of the new geoid. The deep ocean pressure field is also estimated by combining the calculated dynamic ocean topography with hydrography. Finally, the derived circulation is compared to independent observations of the circulation from sea surface drifters and subsurface floats. It is shown that the GRACE GGM02 geoid is significantly more accurate for use in estimating the ocean's circulation.