GOCINA products of relevance for GOCE validation and calibration

While variations in the sea surface height and thus in the ocean currents can be derived directly from satellite altimeter data, an assessment of the absolute value of the ocean dynamic topography (and hence the absolute surface circulation) requires that the elevation of a hypothetical ocean at rest, i.e., the geoid , be subtracted from the altimetric mean sea surface height. The typical elevation scale of the dynamic topography is of the order of 0.1 to 1 m. The dilemma is that the precision of present geoid models is of the same size on the scale of many ocean-circulation features. Hence, the calculation of the mean dynamic topography using mean sea surface height and geoid information can not be satisfactory performed for wavelengths less than about 1000 km. In that spatial domain, the geoid model error becomes equal to or larger than the dynamic topography signals. The application of imprecise geoid models to the determination of dynamic topography at shorter spatial-scales can consequently result in the computation of false topographic signals (< 1m) which, in turn, correspond to erroneous transport calculations of several Sv (where 1 Sv = 10 m/s). Transport uncertainties of this magnitude are of significance in climate studies. In this context the Gravity and Ocean Circulation Explorer (GOCE) mission planned for launch in early 2007 is therefore considered to be of significant importance. 1) Also at The University of Bergen, Geophysical Institute, Bergen, Norway