Mean Dynamic Ocean Topography in the Southern Ocean from GRACE and GOCE and Multi-mission Altimeter Data

Abstract

The ocean north of the Antarctic continent is one of the most dynamic ocean areas on our globe. It is also critical for the regulation of the global climate. We compute a high resolution mean dynamical ocean topography (MDT) using geodetic data and derive a detailed model of the global ocean circulation in this crucial area. The MDT is determined using multimission altimeter data and the GRACE/GOCE gravity model GOCO2s. The mean sea surface is observed from joint cross-over adjustment of 17 years of satellite altimetry. The two geodetic gravity missions GRACE and GOCE allow the computation of a global geoid with unprecedented accuracy and spatial resolution. While GRACE greatly improved the accuracy and global consistency of gravity models at long to medium wavelengths, GOCE is adding highly accurate geoid information in the medium wavelength range. The geoid and mean sea surface have been made consistent by a spectral filter. The MDT is represented as a spherical harmonic expansion. This allows us to analyze the oceanographic content in different wavelength bands. In order to assess properties of the MDT and of the derived geostrophic velocity field, velocities are compared with independent data from satellite tracked surface drifters in the area of the Antarctic Circumpolar Current (ACC). The RMS of the differences is less than 9 cm/s even if shortest scales (100 km) are considered. Our study shows that, with just 6 months of GOCE data, we are able to improve significantly the geodetic MDT.