Ocean Surface Wave-Current Signatures From Satellite Altimeter Measurements

Ocean currents can strongly impact the propagation of swell systems. Satellite altimetry routinely provides measurements of ocean surface significant wave heights (Hs). A self-consistent space-scale decomposition is applied to Hs measurements obtained from different altimeters. This method helps reveal overlooked statistical properties at scales less than 100km, where mesoscale and submesoscale upper ocean circulation drives a significant part of the variability in the coupled ocean-atmosphere system. In particular, systematic signatures related to wave-current interactions are clear at global and regional scales. In the Agulhas current system, the proposed space-scale decomposition further reveals organized and persistent patterns. To leading order, the redistribution of swell energy follows the cumulative impact of the large-scale current vorticity field on wave train kinematics. This relationship causes significant swell ray deflection and localized trapping phenomena, which are adequately captured by altimeter measurements. Plain Language Summary Long and energetic surface waves radiating from distant storms may eventually cover a full ocean basin with a lifetime that can extend over a few weeks. Chances are that these swell fields will propagate over regions characterized by strong ambiant upper ocean currents. Resulting interactions can then trigger sea state variability, including the formation of severe crossing sea conditions. To better document these anticipated effects at global and regional scales, a new methodology is applied to best exploit multisatellite altimeter measurements. As obtained, the resulting augmented data sets provide an unprecedented evidence of the co-variability of surface waves and currents over all ocean basins. More regionally, the analysis shows that persistent and localized sea state anomalies in the Agulhas current region are well explained by swell refraction and focusing effects in the variable current stream. The proposed methodology opens new perspectives for studies and applications combining numerical modeling and satellite observations.