A Mean Ocean Dynamic Topography Derived from Altimetry and the Latest GRACE Geoid Model
Saskia Esselborn(1) , Tilo Schöne(1) , and Roland Schmidt(1)
The determination of a precise mean ocean dynamic topography for the
estimation of oceanic transports and the assimilation into ocean circulation
models is still a challenge. For this study we have compiled a new
mean sea surface height model from reprocessed and harmonized
altimeter data (TOPEX, ERS-1 and ERS-2) and combined it with the
latest static satellite-only GRACE geoid model from GFZ Potsdam
(EIGEN-GRACE_03S). It can be shown that the resulting mean dynamic topography resolves signals down to 400-500km wavelength. For this resolution the derived geostrophic surface currents are still reliable - even for the more noisy meridional component.
The mean dynamic topography is further validated using the WOCE hydrographic climatology. The two data sets show a very good agreement for the resolved spatial scales. This includes the absolute ranges as well as the position of the main current systems. In addition, the satellite-derived data resolve details even on currents of smaller scale like the Gulf Stream Recirculation and the Azores Current. The differences between the two estimates help to identify regions with strong barotropic currents as well as regions where the geoid is not yet adequately determined.