Coral reef drag coefficients—surface gravity wave enhancement
Lentz, Steven J.
Churchill, James H.
Davis, Kristen A.
MetadataShow full item record
A primary challenge in modeling flow over shallow coral reefs is accurately characterizing the bottom drag. Previous studies over continental shelves and sandy beaches suggest surface gravity waves should enhance the drag on the circulation over coral reefs. The influence of surface gravity waves on drag over four platform reefs in the Red Sea is examined using observations from 6-month deployments of current and pressure sensors burst sampling at 1Hz for 4–5min. Depth-average current fluctuations U0 within each burst are dominated by wave orbital velocities uw that account for 80%–90%of the burst variance and have a magnitude of order 10 cm s21, similar to the lower-frequency depth-average current Uavg. Previous studies have shown that the cross-reef bottom stress balances the pressure gradient over these reefs. A bottom stress estimate that neglects the waves (rCdaUavgjUavgj, where r is water density and Cda is a drag coefficient) balances the observed pressure gradient when uw is smaller than Uavg but underestimates the pressure gradient when uw is larger than Uavg (by a factor of 3–5 when uw 5 2Uavg), indicating the neglected waves enhance the bottom stress. In contrast, a bottom stress estimate that includes the waves [rCda(Uavg 1 U0)jUavg 1 U0j)] balances the observed pressure gradient independent of the relative size of uw and Uavg, indicating that this estimate accounts for the wave enhancement of the bottom stress. A parameterization proposed by Wright and Thompson provides a reasonable estimate of the total bottom stress (including the waves) given the burst-averaged current and the wave orbital velocity.
Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018): 1555-1566, doi:10.1175/JPO-D-17-0231.1.
Suggested CitationJournal of Physical Oceanography 48 (2018): 1555-1566
Showing items related by title, author, creator and subject.
Lentz, Steven J.; Fewings, Melanie R.; Howd, Peter A.; Fredericks, Janet J.; Hathaway, Kent (American Meteorological Society, 2008-11)Onshore volume transport (Stokes drift) due to surface gravity waves propagating toward the beach can result in a compensating Eulerian offshore flow in the surf zone referred to as undertow. Observed offshore flows indicate ...
Pressure field induced in the water column by acoustic-gravity waves generated from sea bottom motion Oliveira, Tiago C. A.; Kadri, Usama (John Wiley & Sons, 2016-10-24)An uplift of the ocean bottom caused by a submarine earthquake can trigger acoustic-gravity waves that travel at near the speed of sound in water and thus may act as early tsunami precursors. We study the spatiotemporal ...
Luther, Douglas S. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1980-02)The existence of resonant, baroclinic, equatorially-trapped inertia-gravity waves (discovered by Wunsch and Gill (1976)) is confirmed in the mid-Pacific by spectral analysis of long sea level records. The energy of the ...