Resolving the ubiquitous small-scale semi-permanent features of the general ocean circulation: a multiplatform observational approach

Abstract

Based on 20 years of Argo and ship/animal-borne/glider hydrographic profile data, we derive a new high-resolution hydrographic Atlas and associated circulation field for the oceans above 2000 dbar. Satellite altimetric observations are used to explicitly regress out eddy noise in the fit, greatly reducing one of the major sources of noise. Geostrophic shears are found from the fitted geopotential anomaly fields. Ekman velocities are estimated using satellite wind stresses. Both Argo trajectory observations at 1000 dbar and surface drifter observations are used to reference geostrophic shears derived from the Atlas hydrography. Surface drifter velocities are analyzed with an additional wind friction term to remove the wind-related flow. Agreement between the surface geostrophic (referenced to Argo trajectories) and drifter-based surface velocity is high at both large scales and mesoscales, lending confidence to the derived geostrophic circulation fields. The Atlas reveals standing mesoscale eddies and meanders in western boundary systems and the braided jet structure of the Antarctic Circumpolar Current. In the interior, the upper-ocean flow consists of a highly baroclinic large-scale Sverdrup flow and smaller-scale (∼200-km width) semizonal jets, which are more barotropic (low vertical shear) and have an average zonal width of around 5000 km. These semizonal jets are globally ubiquitous—found in all basins pole to pole. The many permanent mesoscale features of the mean general circulation contrast with that predicted by theories of the large-scale flow in simplified flat-bottomed domains. The Atlas presents a new opportunity to benchmark modern high-resolution ocean and climate models.