The surface thermal signature and air–sea coupling over the Agulhas rings propagating in the South Atlantic Ocean interior

The surface signature of the Agulhas rings propagating across the South Atlantic Ocean is observed based on 3 independent datasets: TMI/AMSR-E satellite sea surface temperature, Argo profiling floats and a merged winds product derived from scatterometer observations and reanalysis results. A persistent pattern of cold (negative) SST anomalies in the eddy core, with warm (positive) anomalies at the boundary is revealed. This pattern contrasts with the classical idea of a warm core anti-cyclone. Taking advantage of a moving reference frame corresponding to the altimetry-detected Agulhas rings, modifications of the surface winds by the ocean induced currents and SST gradients are evaluated using satellite SST and wind observations. As obtained, the averaged stationary thermal expression and mean eddy-induced circulation are coupled to the marine atmospheric boundary layer, leading to surface wind anomalies. Consequently, an average Ekman pumping associated with these mean surface wind variations is consistently emerging. This average Ekman pumping is found to very well explain the SST anomaly signatures of the detected Agulhas rings. Particularly, this mechanism seems to be the key factor determining that these anti-cyclonic eddies exhibit stationary imprints of cold SST anomalies near their core centers. A residual phase with the maximum SSH anomaly and wind speed anomaly is found to the right of the mean wind direction, apparently maintaining a coherent stationary thermal expression coupled to the marine atmospheric boundary layer.