Sea Surface Height Signals as Indicators for Oceanic Meridional Mass Transports

Numerical models are used to test whether the sea surface height (SSH) can be used as an indicator for thevariability of Atlantic meridional oceanic mass transports. The results suggest that if the transports over thewestern boundary current region and those in the eastern part of the basin are considered separately, significantcorrelations (0.3–0.9) are found between zonal SSH differences and the meridional transports in the top1100 m. Much weaker correlations are found for the basinwide transport, which corresponds to the surfacebranch of the meridional overturning circulation (MOC). For the eastern and western branches of the meridionaltransport, combining the SSH signal with the baroclinic structure obtained from Rossby wave theoryenables calculation of a quantitative estimate of the transport variability in the top 1100 m. The results of themethod are less convincing for the variability of the MOC. The reason for this is that even small relative errorsin the variability of the eastern and western branches can be large compared with the MOC variability. Theseerrors project onto the sum of the eastern and western transports and therefore onto the surface branch of theMOC. Nevertheless, being able to infer transport anomalies from SSH signals in the eastern and western partsof the Atlantic might prove useful in interpreting MOC observations from the U.K. Natural EnvironmentResearch Council Rapid Climate Change (RAPID) mooring array at 268N, which show a large subannualvariability that is mainly due to changes at the western boundary. Transports inferred from the SSH could helpto identify the origin of this variability and whether transport anomalies propagate into the western boundaryregion from the basin interior or from other latitudes