Ridge waves
Citable URI
https://hdl.handle.net/1912/5685Location
Juan de Fuca RidgeIceland-Faeroe Ridge
DOI
10.1575/1912/5685Keyword
Ocean wavesAbstract
Second-class wave propagation along mid-ocean ridges is investigated in an effort to
explain subinertial peaks found in the velocity spectra over the Juan de Fuca Ridge
(JdFR, 4 days) and the Iceland-Faeroe Ridge (IFR, 1.8 days). Topographic cross
sections of the ridges are fit by a double-exponential depth profile and the linearized
shallow water equations are solved with the simplified topography. In the northern
hemisphere the western ridge flank supports an infinite set of modes for a topographically
trapped northward propagating wave and the eastern flank supports southward
propagating modes. The eigenfunctions are calculated and dispersion curves are examined
for a variety of ridge profiles. Increasing the slope of a ridge flank increases
the frequencies of the modes it supports. In addition, the waves travelling along the
flanks 'feel' the topography of the opposite side so t hat increasing the width or steepness
of the eastern slope decreases the frequencies of the modes supported by the
western side (and vice versa). The dispersion characteristics of the trapped nondivergent
oscillations allow a zero group velocity (ZGV) so that energy may accumulate
along the ridge as long as the ridge does not approach the isolated shelf profile. Including
divergence lowers the frequencies of the longest waves so that a ZGV may be
found for all ridge profiles. The nature of the effects of stratification, represented by
a two-layer model, are explored by a perturbation procedure for weak stratification.
The 0(1) barotropic basic state is accompanied by an 0(E2) baroclinic perturbation.
The frequencies of the barotropic modes are increased and the velocities are
bottom-trapped. For reasonable values of stratification, however, this effect is small.
Plugging the JdFR topography into the models produces an approximate 4-day ZGV
wave with wavelengths between 1500 and 4500 km. The IFR oscillation, however,
appears to be better modelled by a topographic-Rossby mode model. (Miller et al., 1996) The ridge wave models discussed here also predict the observed anticyclonic
velocity ellipses over the ridge and horizontal decay away from the ridge crest.
Description
Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 1997
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Suggested Citation
Thesis: Harrington, Stephanie A., "Ridge waves", 1997-06, DOI:10.1575/1912/5685, https://hdl.handle.net/1912/5685Related items
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