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Ocean Surface Topography from Space
Altimetric Studies of Ocean Surface Tides and Internal Tides
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Richard Ray
(NASA/Goddard Space Flight Center)

Gary Egbert
(Oregon State University)
Edward Zaron
(Portland State University)


This research uses satellite altimetry and other data to study both surface and internal ocean tides. Special emphasis is given to the study of open-ocean internal tides, their variability and energetics, and the improved determination of shallow-water tides. Owing in part to our previous investigations, internal tides are thought to play an important role in deep ocean turbulence, diapycnal mixing, and the maintenance of abyssal stratification. A precise account of the energy fluxes to these processes, however, is far from clear. Studies of internal-tide generation, propagation, dissipation, and variability should shed much light on the question, and altimetry provides an invaluable dataset for obtaining global and quantitative constraints. Moreover, the question of variability of low-mode internal tides has important implications especially for future wide-swath altimeter missions; it determines whether the altimetry can be corrected for internal tides by using swath data themselves, or must be left uncorrected (but allowed for). We use a combination of approaches involving 3D modeling, empirical mapping, model/data comparisons, and data assimilation to address these problems. In addition, because we have recently developed useful techniques for mapping compound tides, we are continuing that work, which will lead to improved surface tide models, particularly in shallow seas. This, of course, benefits all users of altimetry, as well as significant portions of the entire geophysical community. We also believe it is timely to revisit the small fortnightly Mf tide, since this tide has just recently (in June 2006) reached its 18.6-year maximum amplitude, leading to much improved signal:noise in our data. Our previous work with Mf led to an understanding of its basin-wide characteristics in terms of simple kinematics and geostrophy, but an improved mapping may lead to better understanding of frictional and dissipative effects. Finally, in order to contribute to the OSTST's calibration activities for Jason-2, we will compare the significant wave height data against buoy data and other altimetry, and to untangle some previously published, but contradictory, results involving Jason-1.

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