The observed signature of mesoscale eddies in sea surface temperature and the associated heat transport

Abstract

An estimate of the signature of mesoscale motions in sea surface temperature (SST) is provided for the North Atlantic and the Southern Ocean by analysing the relationship between satellite microwave SST and multi-altimeter sea surface height (SSH) observations. After a preliminary analysis at fixed location, the study focuses on the SST/SSH relationship following eddy tracks.At fixed location, the clearest signature of mesoscale motions in SST is found in regions of large SSH variability, roughly coincident with the major fronts of the Gulf Stream and the Antarctic Circumpolar Current (ACC). Large-scale, likely atmospherically forced, variability masks a major part of the mesoscale signature in SST in more quiescent parts of the World Ocean.Following eddy tracks allows us to detect the signature of mesoscale motions in SST even in regions of weak SSH variability. The track-following analysis reveals robust westward phase shifts of the eddies' SST anomalies with respect to their rotating cores in all regions. In energetic regions, the observed intense warm-top anticyclones and cold-top cyclones are only nearly in-phase, whereas in quiet regions, weaker SST signatures are almost in quadrature with the eddies' SSH.Propagating eddies are found to flux heat poleward in the mixed-layer over a broad range of oceanic regimes and the size of this heat transport is particularly significant in the ACC region (≥0.2PW). Although eddy shedding from major currents is appealing as a mechanism for heat transport (“drift” heat transport), we find that the poleward (equatorward) motion of warm anticyclones (cold cyclones) produces a much weaker poleward heat transport in the mixed layer than that resulting from the westward phase shift between SST and SSH fluctuations (“swirl” heat transport). Associated diffusivities, modest in quiescent interiors (κ<1000m2s−1), intermediate in the ACC (1200m2s−1) and large in the Gulf Stream (≃3000m2s−1), thus primarily reflect the eddy swirl heat transport.