Modeling of very low frequency motions during RIPEX

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Author
Reniers, A.J.H.M.
MacMahan, J.H.
Thornton, E.B.
Stanton, Timothy P.
Date
2007Metadata
Show full item recordAbstract
Numerical computations are used to explain the presence of Very Low Frequency
motions (VLF's), with frequencies less than 0:004 Hz, in the rip current velocity
signals observed during the RIPEX ¯eld experiment. Observations show that the
VLF-motions are most intense within the surfzone and then quickly taper o® in the
o®shore direction. By comparing computed VLF-intensity (Urms;vlf ) distributions in
both the cross-shore and alongshore direction with observations in a qualitative sense,
the most important contributions to the VLF-dynamics are established. VLF-motions
at neighboring rip-channels are seen to interact in the computations, with stronger
surfzone intensity for increasing bathymetric variation. The intermittent forcing by
spatially varying wave-groups is essential in obtaining the correct Urms;vlf distribution
in the cross-shore direction suggesting this is the predominant mechanism responsible
for the generation of the VLF-motions observed during RIPEX. Computations also
suggest that VLF-motions can occasionally propagate o®shore but are mostly con¯ned
to the surfzone corresponding to surfzone eddies.
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