Publications

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2006
Thomson, J, Elgar S, Raubenheimer B, Herbers THC, Guza RT.  2006.  Tidal modulation of infragravity waves via nonlinear energy losses in the surfzone. Geophysical Research Letters. 33   10.1029/2005gl025514   AbstractWebsite

The strong tidal modulation of infragravity (200 to 20 s period) waves observed on the southern California shelf is shown to be the result of nonlinear transfers of energy from these low-frequency long waves to higher-frequency motions. The energy loss occurs in the surfzone, and is stronger as waves propagate over the convex low-tide beach profile than over the concave high-tide profile, resulting in a tidal modulation of seaward-radiated infragravity energy. Although previous studies have attributed infragravity energy losses in the surfzone to bottom drag and turbulence, theoretical estimates using both observations and numerical simulations suggest nonlinear transfers dominate. The observed beach profiles and energy transfers are similar along several km of the southern California coast, providing a mechanism for the tidal modulation of infragravity waves observed in bottom-pressure and seismic records on the continental shelf and in the deep ocean.

Henderson, SM, Guza RT, Elgar S, Herbers THC, Bowen AJ.  2006.  Nonlinear generation and loss of infragravity wave energy. Journal of Geophysical Research-Oceans. 111   10.1029/2006jc003539   AbstractWebsite

[1] 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.

2002
Sheremet, A, Guza RT, Elgar S, Herbers THC.  2002.  Observations of nearshore infragravity waves: Seaward and shoreward propagating components. Journal of Geophysical Research-Oceans. 107   10.1029/2001jc000970   AbstractWebsite

[1] The variation of seaward and shoreward infragravity energy fluxes across the shoaling and surf zones of a gently sloping sandy beach is estimated from field observations and related to forcing by groups of sea and swell, dissipation, and shoreline reflection. Data from collocated pressure and velocity sensors deployed between 1 and 6 m water depth are combined, using the assumption of cross-shore propagation, to decompose the infragravity wave field into shoreward and seaward propagating components. Seaward of the surf zone, shoreward propagating infragravity waves are amplified by nonlinear interactions with groups of sea and swell, and the shoreward infragravity energy flux increases in the onshore direction. In the surf zone, nonlinear phase coupling between infragravity waves and groups of sea and swell decreases, as does the shoreward infragravity energy flux, consistent with the cessation of nonlinear forcing and the increased importance of infragravity wave dissipation. Seaward propagating infragravity waves are not phase coupled to incident wave groups, and their energy levels suggest strong infragravity wave reflection near the shoreline. The cross-shore variation of the seaward energy flux is weaker than that of the shoreward flux, resulting in cross-shore variation of the squared infragravity reflection coefficient (ratio of seaward to shoreward energy flux) between about 0.4 and 1.5.

1999
Sheremet, A, Guza RT.  1999.  A weakly dispersive edge wave model. Coastal Engineering. 38:47-52.   10.1016/s0378-3839(99)00022-8   AbstractWebsite

We derive a general linear, weakly dispersive, Boussinesq-type equation that can be used to study edge waves on beaches with slow cross-shore variation of the depth and the alongshore current. The equation is more accurate than the non-dispersive shallow water equations and simpler than the fully dispersive elliptic mild slope equation (especially for a non-zero alongshore current). The improved performance of the new Boussinesq-type model is demonstrated using analytic solutions for edge waves on a plane beach with zero alongshore current. (C) 1999 Elsevier Science B.V. All rights reserved.

1992
Elgar, S, Herbers THC, Okihiro M, Oltmanshay J, Guza RT.  1992.  Observations of Infragravity Waves. Journal of Geophysical Research-Oceans. 97:15573-15577.   10.1029/92jc01316   AbstractWebsite

Infragravity-wave (periods of one-half to a few minutes) energy levels observed for about 1 year in 8-water depth in the Pacific and in 8- and 13-m depths in the Atlantic are highly correlated with energy in the swell-frequency band (7- to 20-s periods), suggesting the infragravity waves were generated locally by the swell. The amplification of infragravity-wave energy between 13- and 8-m depth (separated by 1 km in the cross shore) is about 2, indicating that the observed infragravity motions am dominated by free waves, not by group-forced bound waves, which in theory are amplified by an order of magnitude in energy between the two locations. However, bound waves am more important for the relatively few cam with very energetic swell, when the observed amplification between 13- and 8-m depth of infragravity-wave energy was sometimes 3 times greater than expected for free waves. Bispectra are consistent with increased coupling between infragravity waves and groups of swell and sea for high-energy incident waves.

Okihiro, M, Guza RT, Seymour RJ.  1992.  Bound Infragravity Waves. Journal of Geophysical Research-Oceans. 97:11453-11469.   10.1029/92jc00270   AbstractWebsite

Model predictions of bound (i.e. nonlinearly forced by and coupled to wave groups) infragravity wave energy are compared with about 2 years of observations in 8- to 13-m depths at Imperial Beach. California, and Barbers Point. Hawaii. Frequency-directional spectra of free waves at sea and swell frequencies, estimated with a small array of four pressure sensors, are used to predict the bound wave spectra below 0.04 Hz. The predicted total bound wave energy is always less than the observed infragravity energy, and the underprediction increases with increasing water depth and especially with decreasing swell energy. At most half, and usually much less, of the observed infragravity energy is bound. Bound wave spectra am also predicted with data from a single wave gage in 183-m depth at Point Conception, California, and the assumption of unidirectional sea and swell. Even with energetic swell, less than 10% of the total observed infragravity energy in 183-m depth is bound. Free waves, either leaky or edge waves, are more energetic than bound waves at both the shallow and deep sites. The low level of infragravity energy observed in 183-m depth compared with 8- to 13-m depths, with similarly moderate sea and swell energy, suggests that leaky (and very high-mode edge) waves contribute less than 10% of the infragravity energy in 8-13 m. Most of the free infragravity energy in shallow water is refractively trapped and does not reach deep water.