An Estimate of Tidal Energy Lost to Turbulence at the Hawaiian Ridge

DOI PDF 5 Citations
  • Jody M. Klymak
    Scripps Institution of Oceanography, La Jolla, California
  • James N. Moum
    College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon
  • Jonathan D. Nash
    College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon
  • Eric Kunze
    Applied Physics Laboratory, and School of Oceanography, University of Washington, Seattle, Washington
  • James B. Girton
    Applied Physics Laboratory, and School of Oceanography, University of Washington, Seattle, Washington
  • Glenn S. Carter
    Applied Physics Laboratory, and School of Oceanography, University of Washington, Seattle, Washington
  • Craig M. Lee
    Applied Physics Laboratory, and School of Oceanography, University of Washington, Seattle, Washington
  • Thomas B. Sanford
    Applied Physics Laboratory, and School of Oceanography, University of Washington, Seattle, Washington
  • Michael C. Gregg
    Applied Physics Laboratory, and School of Oceanography, University of Washington, Seattle, Washington

Abstract

<jats:title>Abstract</jats:title> <jats:p>An integrated analysis of turbulence observations from four unique instrument platforms obtained over the Hawaiian Ridge leads to an assessment of the vertical, cross-ridge, and along-ridge structure of turbulence dissipation rate and diffusivity. The diffusivity near the seafloor was, on average, 15 times that in the midwater column. At 1000-m depth, the diffusivity atop the ridge was 30 times that 10 km off the ridge, decreasing to background oceanic values by 60 km. A weak (factor of 2) spring–neap variation in dissipation was observed. The observations also suggest a kinematic relationship between the energy in the semidiurnal internal tide (E) and the depth-integrated dissipation (D), such that D ∼ E1±0.5 at sites along the ridge. This kinematic relationship is supported by combining a simple knife-edge model to estimate internal tide generation, with wave–wave interaction time scales to estimate dissipation. The along-ridge kinematic relationship and the observed vertical and cross-ridge structures are used to extrapolate the relatively sparse observations along the length of the ridge, giving an estimate of 3 ± 1.5 GW of tidal energy lost to turbulence dissipation within 60 km of the ridge. This is roughly 15% of the energy estimated to be lost from the barotropic tide.</jats:p>

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