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Observations of the Bottom Boundary Layer beneath the World's Largest Internal Solitary Waves
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  • John H Trowbridge,
  • Karl R. Helfrich,
  • D. Benjamin Reeder,
  • Grace Medley,
  • Ming-Huei Chang,
  • Sen Jan,
  • Steven Richard Ramp,
  • Yiing Jang Yang
John H Trowbridge
Woods Hole Oceanographic Institution

Corresponding Author:[email protected]

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Karl R. Helfrich
WHOI
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D. Benjamin Reeder
Naval Postgraduate School
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Grace Medley
Woods Hold group, Inc
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Ming-Huei Chang
National Taiwan University
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Sen Jan
National Taiwan University
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Steven Richard Ramp
Soliton Oceans Services, LLC
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Yiing Jang Yang
National Taiwan University
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Abstract

Measurements in the South China Sea reveal the structure of the bottom boundary layer beneath onshore propagating highly nonlinear internal solitary waves of depression. Offshore directed free stream velocities beneath thirteen waves with durations of 10-20 minutes and velocities up to 1.4 m/s are consistent with the solitary wave solution to the Korteweg de Vries equation, as are phase velocities estimated from pressures and free stream velocities. The measurements indicate a thin layer during free stream acceleration, a thicker layer with an inflected velocity during deceleration, and a long lived sediment laden wake, after wave passage in the free stream, with velocities opposite those at maximum flow strength. Reynolds averaged Navier Stokes simulations with the k-ε turbulence model reproduce the measured velocities and turbulent Reynolds shear stresses accurately during acceleration and early deceleration. However, differences between the simulations and the measurements during late deceleration and in the wake suggest energetic large scale turbulence not represented by the simulations. This turbulence might be similar in origin to coherent vortices that have been observed in laboratory experiments and direct numerical simulations at much smaller Reynolds numbers, which have been attributed to absolute and global instabilities resulting from inflected velocity profiles.