Direct Breaking of the Internal Tide near Topography: Kaena Ridge, Hawaii
Journal of Physical Oceanography (2008)
- ISSN: 00223670
- DOI: 10.1175/2007JPO3728.1
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Direct Breaking of the Internal Tide near Topography: Kaena Ridge, Hawaii
Direct breaking of the internal tide near topography:
Kaena Ridge, Hawaii
JODY M. KLYMAK1, ROBERT PINKEL2, AND LUC RAINVILLE3
1University of Victoria, Victoria, B.C.
2Scripps Institution of Oceanography, La Jolla CA
3Woods Hole Oceanographic Institution, Woods Hole MA
Submitted, Journal of Physical Oceanography, April 17, 2007
April 17, 2007
Corresponding author address:
J. Klymak, School of Earth and Ocean Sciences, University of Victoria, P.O. Box 3055
STN CSC, Victoria, B.C., Canada, V8W 3P6, jklymak@uvic.ca
1
Kaena Ridge, Hawaii
JODY M. KLYMAK1, ROBERT PINKEL2, AND LUC RAINVILLE3
1University of Victoria, Victoria, B.C.
2Scripps Institution of Oceanography, La Jolla CA
3Woods Hole Oceanographic Institution, Woods Hole MA
Submitted, Journal of Physical Oceanography, April 17, 2007
April 17, 2007
Corresponding author address:
J. Klymak, School of Earth and Ocean Sciences, University of Victoria, P.O. Box 3055
STN CSC, Victoria, B.C., Canada, V8W 3P6, jklymak@uvic.ca
1
Page 2
2 JOURNAL OF PHYSICAL OCEANOGRAPHY VOLUME
ABSTRACT
Barotropic to baroclinic conversion and attendant phenomena were recently exam-
ined at the Kaena Ridge as an aspect of the Hawaii Ocean Mixing Experiment. Two
distinct mixing processes appear to be at work in the waters above the 1100-m deep
ridge crest. At mid-depths, above 800 m, mixing events resemble their open ocean
counterparts. There is no apparent modulation of mixing rates with the fortnightly
cycle and they are well-modeled by standard open-ocean parameterizations. Nearer
to the topography, there is quasi-deterministic breaking associated with each baro-
clinic crest passage. Large amplitude small-scale internal waves are triggered by
tidal forcing, consistent with lee wave formation at the ridge-break. These waves
have vertical wavelengths on the order of 400-m. During spring tides the waves are
non-linear and exhibit convective instabilities on their leading edge. Dissipation
rates exceed those predicted by the open-ocean parameterizations by up to a factor
of 100, with the disparity increasing as the seafloor is approached.
These observations are based on a set of repeated CTD and microconductivity pro-
files obtained from the R/P FLIP which was tri-moored over the southern edge of
the ridge crest. Ocean velocity and shear was resolved to 4-m vertical scale by
a suspended Doppler sonar. Dissipation was estimated both by measuring over-
turn displacements and from microconductivity wavenumber spectra. The methods
agreed deeper than 200 m where sensor resolution limitations do not limit the tur-
bulence estimates. At intense mixing sites new phenomena await discovery and
existing parameterizations cannot be expected to work.
ABSTRACT
Barotropic to baroclinic conversion and attendant phenomena were recently exam-
ined at the Kaena Ridge as an aspect of the Hawaii Ocean Mixing Experiment. Two
distinct mixing processes appear to be at work in the waters above the 1100-m deep
ridge crest. At mid-depths, above 800 m, mixing events resemble their open ocean
counterparts. There is no apparent modulation of mixing rates with the fortnightly
cycle and they are well-modeled by standard open-ocean parameterizations. Nearer
to the topography, there is quasi-deterministic breaking associated with each baro-
clinic crest passage. Large amplitude small-scale internal waves are triggered by
tidal forcing, consistent with lee wave formation at the ridge-break. These waves
have vertical wavelengths on the order of 400-m. During spring tides the waves are
non-linear and exhibit convective instabilities on their leading edge. Dissipation
rates exceed those predicted by the open-ocean parameterizations by up to a factor
of 100, with the disparity increasing as the seafloor is approached.
These observations are based on a set of repeated CTD and microconductivity pro-
files obtained from the R/P FLIP which was tri-moored over the southern edge of
the ridge crest. Ocean velocity and shear was resolved to 4-m vertical scale by
a suspended Doppler sonar. Dissipation was estimated both by measuring over-
turn displacements and from microconductivity wavenumber spectra. The methods
agreed deeper than 200 m where sensor resolution limitations do not limit the tur-
bulence estimates. At intense mixing sites new phenomena await discovery and
existing parameterizations cannot be expected to work.
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