Henderson Stephen M.

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Henderson
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Stephen M.
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  • Article
    Nonlinear generation and loss of infragravity wave energy
    (American Geophysical Union, 2006-12-08) Henderson, Stephen M. ; Guza, R. T. ; Elgar, Steve ; Herbers, T. H. C. ; Bowen, A. J.
    Nonlinear energy transfers with sea and swell (frequencies 0.05–0.40 Hz) were responsible for much of the generation and loss of infragravity wave energy (frequencies 0.005–0.050 Hz) observed under moderate- and low-energy conditions on a natural beach. Cases with energetic shear waves were excluded, and mean currents, a likely shear wave energy source, were neglected. Within 150 m of the shore, estimated nonlinear energy transfers to (or from) the infragravity band roughly balanced the divergence (or convergence) of the infragravity energy flux, consistent with a conservative energy equation. Addition of significant dissipation (requiring a bottom drag coefficient exceeding about 10−2) degraded the energy balance.
  • Article
    Refraction of surface gravity waves by shear waves
    (American Meteorological Society, 2006-04) Henderson, Stephen M. ; Guza, R. T. ; Elgar, Steve ; Herbers, T. H. C.
    Previous field observations indicate that the directional spread of swell-frequency (nominally 0.1 Hz) surface gravity waves increases during shoreward propagation across the surf zone. This directional broadening contrasts with the narrowing observed seaward of the surf zone and predicted by Snell’s law for bathymetric refraction. Field-observed broadening was predicted by a new model for refraction of swell by lower-frequency (nominally 0.01 Hz) current and elevation fluctuations. The observations and the model suggest that refraction by the cross-shore currents of energetic shear waves contributed substantially to the observed broadening.