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Ocean Surface Topography from Space
An Investigation of Global Mesoscale Variability
Dudley Chelton
(Oregon State University)

Roger Samelson
(Oregon State University)
Representative maps of North Pacific SSH on 21 August 1996 constructed from T/P data alone (left) and
									from the merged T/P and ERS-1 data (right).
Larger image with caption


Extensive observational and theoretical work over the past decade has focused on dynamical interpretation of observations of SSH from the TOPEX/Poseidon (T/P) altimeter as linear Rossby waves modified by background mean currents and bottom topography. The doubling of resolution afforded by merging the measurements from two simultaneously operating altimeters reveals previously unresolved features that suggest a paradigm shift to a view of the ocean as being dominated by nonlinear eddies rather than Rossby waves. Altimetry is the only way to obtain essentially synoptic, global observations of the eddies.

The objective of this research is to validate and extend an automated eddy identification and tracking procedure and apply it globally to altimeter data and to the output of eddy-resolving ocean general circulation models (OGCMs), in order to investigate the dynamics of mesoscale variability. The procedure we are using is the fifth in a hierarchy of procedures that we have developed, each of which addressed issues of concern in previous versions. While we believe that our current procedure is robust and produces eddy trajectories that can be interpreted dynamically, continued testing and verification, and possible further refinements, will be conducted as part of this research. Application to the output of OGCMs allows quantification of the strengths and limitations of the procedure in the presence of known sampling errors and measurement noise in the altimeter data. The OGCMs also provide information about subsurface variability, which is essential to understanding some of the dynamical questions about mesoscale variability. An important aspect of this research is the investigation of the degree to which the subsurface characteristics of eddies can be inferred from SSH measurements alone. The host of dynamical questions to be addressed in this research will lead to a greatly improved understanding of mesoscale and large-scale ocean circulation.

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