Dooley
Ciara J.
Dooley
Ciara J.
No Thumbnail Available
Search Results
Now showing
1 - 3 of 3
-
ArticleObservations of two-dimensional turbulence in the surfzone(American Institute of Physics, 2023-08-30) Elgar, Steve ; Dooley, Ciara ; Gorrell, Levi ; Raubenheimer, BrittLow-frequency, many-minute-period horizontal surfzone eddies are an important mechanism for the dispersion of material, transporting larvae, pollutants, sediment, and swimmers both across and along the nearshore. Previous numerical, laboratory, and field observations on alongshore uniform bathymetry with no or roughly uniform mean background flows suggest that the low-frequency eddies may be the result of a two-dimensional inverse energy cascade that transfers energy from relatively small spatial-scale vorticity injected by depth limited breaking waves to larger and larger spatial scales. Here, using remotely sensed high-spatial resolution estimates of currents, those results are extended to surfzones with strong complex mean circulation patterns [flows O(1 m/s)] owing to nonuniform bathymetry. Similar to previous results, wavenumber spectra and second-order structure functions calculated from the observations are consistent with a two-dimensional inverse energy cascade. The size of the largest eddies is shown to depend on the surfzone width and the spatial scales of the mean currents. Third-order structure functions also are consistent with an inverse cascade for spatial scales greater than ∼50 m. At smaller scales, the third-order structure functions suggest a mixture of inverse and forward cascades.
-
ThesisObservations of surfzone vorticity using optical remote sensing(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2025-02) Dooley, Ciara J. ; Elgar, Steve ; Raubenheimer, BrittThe surfzone is the dynamic interface between the land and ocean, where waves shoal and break as they reach shallow water near the shore. Currents and circulation patterns in the surfzone transport sediment, nutrients, pollutants, and other materials along and across the coast, and can create hazardous conditions for swimmers (rip currents). However, understanding of the strength and structure of eddies and vortices in the flow field primarily remains limited to numerical models and theory. Here, novel observations of surfzone vorticity at small [O(10m)] and large [O(100m)] spatial scales are presented and related to incident wave conditions and the measured underlying bathymetry. Field experiments were conducted at a sandy beach on the Atlantic Ocean, and nearshore flows were observed using optical remote sensing (coastal imaging) and in situ sensors. Remote sensing algorithms are expanded from previous applications to estimate high spatial resolution two-dimensional surface flows by tracking the motion of naturally occurring foam throughout the surfzone. Estimated currents are correlated with in situ flow measurements, and errors increase as the sea-surface viewing angle becomes more oblique and image quality decreases. Large spatial-scale vorticity estimated using remotely sensed flows increases with alongshore bathymetric inhomogeneity, and complex circulation patterns corresponding to holes and channels in the seafloor persist for days at a time. Small spatial-scale vorticity estimated from a 5-m diameter ring of 14 current meters increases with the directional spread of the incident wave field, consistent with increased vorticity injection from the crest-ends of breaking waves. Small spatial-scale vorticity estimated using remotely sensed flows is spatially variable and correlated with the amount of wave breaking observed at a given location. Enhanced vorticity at large and small spatial scales occurs in the inner surfzone, and virtual drifters released into the remotely sensed flow fields demonstrate cross-shore variability in dispersion and mixing. This thesis expands the understanding of vorticity dynamics in the surfzone through unique field observations and provides new tools for coastal research and monitoring through development of remote sensing techniques.
-
ArticleField observations of surfzone vorticity(American Geophysical Union, 2024-10-28) Dooley, Ciara J. ; Elgar, Steve ; Raubenheimer, BrittIn the surfzone, breaking-wave generated eddies and vortices transport material along the coast and offshore to the continental shelf, providing a pathway from land to the ocean. Here, surfzone vorticity is investigated with unique field observations obtained during a wide range of wave and bathymetric conditions on an Atlantic Ocean beach. Small spatial-scale [O(10 m)] vorticity estimated with a 5 m diameter ring of 14 current meters deployed in ∼2 m water depth increased as the directional spread of the wave field increased. Large spatial-scale [O(100 m)] vorticity calculated from remote sensing estimates of currents across the surfzone along 200 m of the shoreline increased as alongshore bathymetric variability (channels, bars, bumps, holes) increased. For all bathymetric conditions, large-scale vorticity in the inner surfzone was more energetic than in the outer surfzone.