HR: 16:00h
AN: OS14B-01    [Abstracts]
TI: Observations of Wave Reflection from a Submarine Canyon
AU: * Thomson, J
EM: jthomson@whoi.edu
AF: MIT-WHOI Joint Program, Woods Hole Oceanographic Institution, MS 9, Woods Hole, MA 02543 United States
AU: Elgar, S
EM: elgar@whoi.edu
AF: Applied Ocean Physics & Engineering, Woods Hole Oceanographic Institution, MS 11, Woods Hole, MA 02543 United States
AU: Herbers, T
EM: thherber@nps.edu
AF: Department of Oceanography, Naval Postgraduate School, Monterey, CA 93943-5122 United States
AB: Observations in 20-m water depth near the sides of the steep-walled (350-m wide, 120-m deep) La Jolla submarine canyon suggest abrupt shallow-water bathymetry can reflect surface-gravity waves. Reflection coefficients estimated by applying a newly developed inverse algorithm to observations of pressure and velocity at each side of the canyon are consistent with theoretical predictions of reflection by a rectangular canyon in shallow water [Kirby and Dalrymple, {\it J. Fluid Mech.}, {\bf 133}, 1983]. The inverse algorithm estimates reflection as a function of the frequency and directional spectrum of the incident waves. Here, analysis was restricted to infragravity frequencies (periods of order one minute, wavelengths of several hundred meters), because predicted reflection is maximized for wavelengths similar to the canyon width. For the rarely observed cases of normally incident (relative to the canyon axis) waves with narrow directional spread, the observations agree well with theory, including the absence of reflection for wavelengths that are integer multiples of the canyon width. In the more commonly observed cases of obliquely incident waves with large directional bandwidth, the observed reflection is less than predicted, and the complete reflection hypothesized to occur for highly oblique waves is not observed. When averaged over all observed wave conditions, La Jolla Canyon reflected more than half of the incident infragravity energy, and thus may be important to infragravity motions at the nearby shoreline. Supported by the Office of Naval Research and the National Science Foundation.
DE: 4546 Nearshore processes
DE: 4560 Surface waves and tides (1255)
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting