Thornton Ed B.

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Thornton
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Ed B.
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  • Article
    Fortnightly tides and subtidal motions in a choked inlet
    (Elsevier, 2014-04-12) MacMahan, Jamie ; van de Kreeke, Jacobus ; Reniers, Ad ; Elgar, Steve ; Raubenheimer, Britt ; Thornton, Ed B. ; Weltmer, Micah ; Rynne, Patrick ; Brown, Jenna
    Amplitudes of semi-diurnal tidal fluctuations measured at an ocean inlet system decay nearly linearly by 87% between the ocean edge of the offshore ebb-tidal delta and the backbay. A monochromatic, dynamical model for a tidally choked inlet separately reproduces the evolution of the amplitudes and phases of the semi-diurnal and diurnal tidal constituents observed between the ocean and inland locations. However, the monochromatic model over-predicts the amplitude and under-predicts the lag of the lower-frequency subtidal and fortnightly motions observed in the backbay. A dimensional model that considers all tidal constituents simultaneously, balances the along-channel pressure gradient with quadratic bottom friction, and that includes a time-varying channel water depth, is used to show that that these model-data differences are associated with nonlinear interactions between the tidal constituents that are not included in non-dimensional, monochromatic models. In particular, numerical simulations suggest that the nonlinear interactions induced by quadratic bottom friction modify the amplitude and phase of the subtidal and fortnightly backbay response. This nonlinear effect on the low-frequency (subtidal and fortnightly) motions increases with increasing high-frequency (semi-diurnal) amplitude. The subtidal and fortnightly motions influence water exchange processes, and thus backbay temperature and salinity.
  • Preprint
    Estimating nearshore bedform amplitudes with altimeters
    ( 2005-01-14) Gallagher, E. L. ; Elgar, Steve ; Guza, R. T. ; Thornton, Ed B.
    Estimates of the heights of large (0.1-0.4 m heights and 1-10 m horizontal lengths) migrating bedforms on a sandy beach made with fixed, single-point altimeters are similar to heights estimated from profiles across the bedforms made with altimeters mounted on an amphibious vehicle that traversed the surf zone. Unlike many profiling systems, the robust, fixed altimeters can measure bedforms in bubbly, sediment-laden surfzone waters nearly continuously, including during storms, thus allowing investigation of the relationships between bedform heights and near-bottom velocities to be extended to a wide range of wave conditions. The fixed-altimeter observations of migrating bedforms suggest a sandy surfzone seafloor is not always smooth during energetic conditions with strong mean currents and large wave-orbital velocities.