The influence of subinertial internal tides on near-topographic turbulence at the Mendocino Ridge: Observations and modeling

R. C. Musgrave, J. A. MacKinnon, R. Pinkel, A. F. Waterhouse, J. Nash, S. M. Kelly

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Shipboard measurements of velocity and density were obtained in the vicinity of a small channel in the Mendocino Ridge, where flows were predominantly tidal. Measured daily inequalities in transport are much greater than those predicted by a barotropic tide model, with the strongest transport associated with full depth flows and the weakest with shallow, surface-confined flows. A regional numerical model of the area finds that the subinertial K1 (diurnal) tidal constituent generates topographically trapped waves that propagate anticyclonically around the ridge and are associated with enhanced near-topographic K1 transports. The interaction of the baroclinic trapped waves with the surface tide produces a tidal flow whose northward transports alternate between being surface confined and full depth. Full depth flows are associated with the generation of a large-amplitude tidal lee wave on the northward face of the ridge, while surface-confined flows are largely nonturbulent. The regional model demonstrates that, consistent with field observations, near-topographic dissipation over the entire ridge is diurnally modulated, despite the semidiurnal tidal constituent having larger barotropic velocities. It is concluded that at this location it is the bottom-trapped subinertial internal tide that governs near-topographic dissipation and mixing. The effect of the trapped wave on regional energetics is to increase the fraction of converted barotropic-baroclinic tidal energy that dissipates locally.

Original languageEnglish (US)
Pages (from-to)2139-2154
Number of pages16
JournalJournal of Physical Oceanography
Issue number8
StatePublished - 2017

Bibliographical note

Publisher Copyright:
© 2017 American Meteorological Society.


  • Bottom currents
  • Internal waves
  • Mixing
  • Tides
  • Topographic effects


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