Examinando por Autor "Parra S.M."

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    Coherence between infragravity waves and ambient water motions over cape-associated shoals
    (PERGAMON-ELSEVIER SCIENCE LTD, 2019-01-01) Paniagua-Arroyave J.F.; Valle-Levinson A.; Adams P.N.; Parra S.M.; Universidad EAFIT. Departamento de Geología; Ciencias del Mar
    Cross-shelf water motions influence fluxes of nutrients, larvae and sediments, which in turn affect nearshore morphodynamics. Among these motions are infragravity waves, which typically exhibit periodicities from 20 to 200 s, and originate from multiple sources including the superposition of incident wave fields. To examine how infragravity waves co-vary with water motions in an area of complex bathymetry, we analyzed measurements from acoustic Doppler current profilers around cape-associated shoals near Cape Canaveral, on the Florida (USA) Atlantic coast. Observations of water motions and infragravity wave heights at the outer and inner swales of two isolated shoals (Shoal E and Shoal D), located approximately 15 km offshore in ~ 14 m water depth, were subjected to squared coherency and wavelet coherence analyses. Coherences between infragravity wave heights and flow conditions were unsteady, i.e. variable over time, and exhibited differences between outer and inner swales. Subtidal flows (periods > 0.5 days) were sporadically coherent with the total and bound infragravity wave heights at both inner and outer swales. Tidal flows (~ 2 cycles/day) were coherent with the total infragravity wave heights only at outer swale locations. These results indicate that tidal motions may modulate the generation of free (directed both oppositely to and in the direction of short-wave propagation) infragravity waves by short-wave groups shoaling and by refractive trapping at shoals. Subtidal flows, on the other hand, may influence triad interactions that generate infragravity motions. © 2018 Elsevier Ltd
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    Observations of surface-gravity-wave scattering and dissipation by an isolated shoal related to a cuspate foreland
    (PERGAMON-ELSEVIER SCIENCE LTD, 2019-01-01) Paniagua-Arroyave J.F.; Adams P.N.; Parra S.M.; Valle-Levinson A.; Universidad EAFIT. Departamento de Geología; Ciencias del Mar
    Inner-shelf and shoreline morphology exert control on the variability of gravity waves. Although gravity waves can influence nearshore morphodynamics, their behavior is not well understood at inner-shelves close to cuspate forelands with complex bathymetry. In order to study the effects of cape shoals on gravity wave variability, water level and velocity data were collected during Fall 2013, Spring 2014, and Fall 2014 within the swales on either side of Shoal E, near Cape Canaveral, Florida. Short wave energy fluxes (periods from 3 to 20 s, or frequencies from 50 to ~300 mHz) were calculated from time series of spectral densities, whereas cross-shoal infragravity energy fluxes (periods from 20 to 500 s, or frequencies from 2 to 50 mHz) were calculated from cross-spectra of pressure and cross-shoal velocities. Ratios of short-gravity-wave energy fluxes between inner and outer swales of Shoal E ranged from 0.5 to 3. Values < 1 were typically associated to large (wave heights > 1 m) and short waves (periods < 5 s) likely related to dissipation. Ratios > 1 were exhibited by large and long (periods > 10 s) waves because of refraction. Values close to 1 were related to small waves regardless of the wavelength. In addition, infragravity reflection coefficients were quantified as the ratio of seaward to landward infragravity energy fluxes. Reflection coefficients and spatial variations in infragravity fluxes indicate that instruments were located in the shoaling zone during Fall 2013 and Fall 2014. Infragravity energy flux differences between inner and outer swales further suggest Shoal E may have acted as a source of infragravity energy. Differences in reflection between swales on either side of Shoal E could be attributed to asymmetric short-wave shoaling and breaking, partial infragravity reflection, and infragravity energy trapping near the shoal. However, instrument configuration did not allow for along-shoal calculations, which hindered resolution of edge waves that might develop over the shoal. Our results provide evidence, albeit incomplete, of surface-gravity-wave energy scattering and dissipation over cape-related shoals. Such wave transformations, including infragravity energy forcing, may provide a positive feedback for the long-term stability of cuspate forelands by preventing the full complement of deep water wave energy from reaching the shoreline. © 2018 Elsevier Ltd