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Abstract
Geostrophic surface velocity anomalies, inferred from the tandem Jason-1- TOPEX/Poseidon (JTP) altimeter mission, are used to analyze space-time variations of eddy kinetic energy (EKE), eddy momentum, and heat transports in the subpolar North Atlantic. The geostrophic currents are estimated using the “parallel-track approach” with a 10 km along-track resolution. The analysis covers the entire three-year period of the tandem mission (109 repeat cycles) from September 2002 to September 2005. In this paper, we used the three-year record of geostrophic surface velocities available from the JTP tandem mission to estimate eddy transport processes in the subpolar North Atlantic and interpret them in combination with similar results available from a high-resolution numerical simulation of the North Atlantic with a 1/12° horizontal resolution for a 25-year period. Due to the sampling characteristics of the JTP tandem mission, only transports of large-scale eddies can be observed. Moreover, the time series are too short to get statistically stable estimates of eddy processes. Nevertheless, distinct estimates of spatially varying eddy processes can be diagnosed from the novel data set, especially when interpreted in combination with the longer model results. Results suggest that eddy forces accelerate the mean flow over large fractions of the subpolar North Atlantic. There is valuable information present in the JTP velocity time series that contribute to an enhanced understanding of eddy dynamics and the representation of eddy heat and momentum transports in numerical models.
Acknowledgements
We thank Carl Wunsch for helpful comments on an earlier version of the manuscript. Charmaine King (MIT) helped with the processing of the T/P and Jason-1 altimeter data. This work was supported in part by the DFG (project SFB 512, TP E1 and project STA410/7-1) as well as by the BMBF (project “Nordatlantik”, TP 4.1). The altimeter products were produced by Salto/Duacs and distributed by AVISO (http://www.aviso.oceanobs.com/duacs/), with support from CNES.