The new CNES-CLS18 Global Mean Dynamic Topography

Abstract. The Mean Dynamic Topography (MDT) is a key reference surface for altimetry. It is needed for the calculation of the ocean absolute dynamic topography, and under the geostrophic approximation, the estimation of surface currents. CNES-CLS Mean Dynamic Topography (MDT) solutions are calculated by merging information from altimeter data, GRACE and GOCE gravity field and oceanographic in-situ measurements (drifting buoy velocities, hydrological profiles). The objective of this paper is to present the newly updated CNES-CLS18 MDT. The main improvement compared to the previous CNES-CLS13 solution is the use of updated input datasets: the GOCO05S geoid model is used based on the complete GOCE mission (November 2009–October 2013) and 10.5 years of GRACE data, together with all drifting buoy velocities (SVP-type and Argo floats) and hydrological profiles (CORA database) available from 1993–2017 (instead of 1993–2012). The new solution also benefits from improved data processing – in particular a new wind-driven current model has been developed to extract the geostrophic component from the buoy velocities; and methodology – in particular the computation of the medium scale GOCE-based MDT first guess and the correlation scales used for the multivariate mapping have been revised. An evaluation of the new solution compared to the previous version and to other existing MDT show significant improvements both in strong currents and coastal areas.