Model-data comparisons of shear waves in the nearshore
Loading...
Authors
Noyes, T. James
Guza, R. T.
Feddersen, Falk
Elgar, Steve
Herbers, T.H.C.
Subjects
Advisors
Date of Issue
2005-05-27
Date
Publisher
American Geophysical Union
Language
en_US
Abstract
Observations of shear waves, alongshore propagating meanders of the mean alongshore current with periods of a few minutes and alongshore wavelengths of a few hundred meters, are compared with model predictions based on numerical solutions of the nonlinear shallow water equations. The model (after Özkan-Haller and Kirby (1999)) assumes alongshore homogeneity and temporally steady wave forcing and neglects wave-current interactions, eddy mixing, and spatial variation of the (nonlinear) bottom drag coefficient. Although the shapes of observed and modeled shear wave velocity spectra differ, and root-mean-square velocity fluctuations agree only to within a factor of about 3, aspects of the cross-shore structure of the observed (∼0.5–1.0 m above the seafloor) and modeled (vertically integrated) shear waves are qualitatively similar. Within the surf zone, where the mean alongshore current (V) is strong and shear waves are energetic, observed and modeled shear wave alongshore phase speeds agree and are close to both V and C lin (the phase speed of linearly unstable modes) consistent with previous results. Farther offshore, where V is weak and observed and modeled shear wave energy levels decay rapidly, modeled and observed C diverge from C lin and are close to the weak alongshore current V. The simulations suggest that the alongshore advection of eddies shed from the strong, sheared flow closer to shore may contribute to the offshore decrease in shear wave phase speeds. Similar to the observations, the modeled cross- and alongshore shear wave velocity fluctuations have approximately equal magnitude, and the modeled vorticity changes sign across the surf zone.
Type
Article
Description
The article of record as published may be found at https://doi.org/10.1029/2004JC002541
Series/Report No
Department
Organization
Identifiers
NPS Report Number
Sponsors
This research was supported by the Office
of Naval Research, the National Oceanographic Partnership Program, and
the National Science Foundation.
Funder
Format
Citation
Journal of Geophysical Research 110 (2005): C05019, doi:10.1029/2004JC002541.
Journal of Geophysical Research 110 (2005): C05019
Journal of Geophysical Research 110 (2005): C05019