New Global Mean Dynamic Topography CNES-CLS-22 Combining Drifters, Hydrography Profiles and High Frequency Radar Data

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 MDT solutions are calculated by merging information from altimeter data, GRACE, and GOCE gravity field and oceanographic in situ measurements (drifting buoy velocities, High Frequency radar surface velocities, hydrological profiles). The objective of this paper is to present the newly updated CNES-CLS22 MDT. The main improvement of this new CNES-CLS22 MDT over the previous CNES-CLS18 MDT is in the Arctic, with better coverage and a more physical solution (with the disappearance of artifacts from the previous version). This is due to the use of a new first guess estimated with the CNES-CLS22 MSS and the GOCO06s geoid to which optimal filtering has been applied, as well as Lagrangian filtering at the coast to reduce the intensity of currents normal to the coast. Improvements also include updating the drifting buoy and T/S profile databases, and processing to obtain synthetic mean geostrophic velocities and synthetic mean heights. In addition, a new data type, HF radar data, was processed to extract physical content consistent with MDT in the Mid Atlantic Bight of the northeast U.S. coastal region. The study of this region in particular has shown the improvements of the CNES-CLS22 MDT, though there is still work to be done to obtain a more physical solution over the continental shelf. The CNES-CLS22 MDT has been evaluated against independent height and velocity data in comparison with the previous version, the CNES-CLS18. The new solution presents slightly better results, although not identical in all regions of the globe.