Reconstructing the Ocean's Interior from Surface Data

A new method is proposed for extrapolating subsurface velocity and density fields from sea surface density and sea surface height (SSH). In this, the surface density is linked to the subsurface fields via the surface quasigeostrophic (SQG) formalism, as proposed in several recent papers. The subsurface field is augmented by the addition of the barotropic and first baroclinic modes, whose amplitudes are determined by matching to the sea surface height (pressure), after subtracting the SQG contribution. An additional constraint is that the bottom pressure anomaly vanishes. The method is tested for three regions in the North Atlantic using data from a high-resolution numericalsimulation. The decomposition yields strikinglyrealistic subsurfacefields. It is particularly successful in energetic regions like the Gulf Stream extension and at high latitudes where the mixed layer is deep, but it also works in less energetic eastern subtropics. The demonstration highlights the possibility of reconstructing three-dimensional oceanic flows using a combination of satellite fields, for example,seasurfacetemperature(SST)andSSH,andsparse(orclimatological)estimatesoftheregionaldepthresolveddensity.Themethodcouldbefurtherelaboratedtointegrateadditionalsubsurfaceinformation,such as mooring measurements.

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