Beyond GOCE for the ocean circulation estimate: Synergetic use of altimetry, gravimetry, and in situ data provides new insight into geostrophic and Ekman currents

Abstract

Accurate estimate of ocean surface currents is both a challenging issue and a growing end-users requirement. In this paper ocean currents are calculated at two levels (surface and 15 m depth) as the sum of the geostrophic and Ekman components. First, a new, global, 14° Mean Dynamic Topography, called the CNES-CLS13 MDT, has been calculated and is now available for use by the oceanographic community. By exploiting information from surface drifters and Argo floats, the new MDT resolves spatial scales beyond the resolution permitted by the recent Gravity and Ocean Circulation Experiment (GOCE) geoid models (125 km). Associated mean geostrophic speeds in strong currents are increased by 200% on average compared to GOCE-based mean currents. In addition, for the first time, a two-level, monthly, empirical Ekman model that samples a spiral-like behavior is estimated. We show that combining both pieces of information leads to improved ocean currents compared to other existing observed products. Key Points New global Mean Dynamic Topography from GOCE, altimetry, and in situ dataNew two-level Ekman model from the joint analysis of Argo floats and SVP driftersNew ocean currents by combining geostrophy and Ekman at surface and 15m depth