Oceanography The Official Magazine of
The Oceanography Society
Volume 32 Issue 04

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Volume 32, No. 4
Pages 102 - 109

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Turbulence and Vorticity in the Wake of Palau

By Louis St. Laurent , Takashi Ijichi, Sophia T. Merrifield, Justin Shapiro, and Harper L. Simmons 
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Article Abstract

The interaction of flow with steep island and ridge topography at the Palau island chain leads to rich vorticity fields that generate a cascade of motions. The energy transfer to small scales removes energy from the large-scale mean flow of the equatorial current systems and feeds energy to the fine and microstructure scales where instability mechanisms lead to turbulence and dissipation. Until now, direct assessments of the turbulence associated with island wakes have received only minimal attention. Here, we examine data collected from an ocean glider equipped with microstructure sensors that flew in the island wake of Palau. We use a combination of submesoscale modeling and direct observation to quantify the relationship between vorticity and turbulence levels. We find that direct wind-driven mixing only accounts for about 10% of the observed turbulence levels, suggesting that most of the energy for mixing is extracted from the shear associated with the vorticity field in the island’s wake. Below the surface layer, enhanced turbulence correlates with the phase and magnitude of the relative vorticity and strain levels of the mesoscale flow.

Citation

St. Laurent, L., T. Ijichi, S.T. Merrifield, J. Shapiro, and H.L. Simmons. 2019. Turbulence and vorticity in the wake of Palau. Oceanography 32(4):102–109, https://doi.org/10.5670/oceanog.2019.416.

References

Boccaletti, G., R. Ferrari, and B. Fox-Kemper. 2007. Mixed layer instabilities and restratification. Journal of Physical Oceanography 37(9):2,228–2,250, https://doi.org/10.1175/JPO3101.1.

Callies, J., G. Flierl, R. Ferrari, and B. Fox-Kemper. 2016. The role of mixed-layer instabilities in submesoscale turbulence. Journal of Fluid Mechanics 788:5–41, https://doi.org/10.1017/jfm.2015.700.

Chang, M.-H., T.Y. Tang, C.-R. Ho, and S.-Y. Chao. 2013. Kuroshio-induced wake in the lee of Green Island off Taiwan. Journal of Geophysical Research 118(3):1,508–1,519, https://doi.org/10.1002/jgrc.20151.

Colin, P.L. 2018. Ocean warming and the reefs of Palau. Oceanography 31(2):126–135, https://doi.org/​10.5670/oceanog.2018.214.

Cummings, J.A., and O.M. Smedstad. 2013. Variational data assimilation for the global ocean. Pp. 303–343 in Data Assimilation for Atmospheric, Oceanic and Hydrologic Applications, vol. II. S.K. Park and L. Xu, eds, Springer-Verlag Berlin Heidelberg.

Fairall, C.W., E.F. Bradley, J.E. Hare, A.A. Grachev, and J.B. Edson. 2003. Bulk parameterization of air-sea fluxes: Updates and verification for the COARE algorithm. Journal of Climate 16:571–591, https://doi.org/10.1175/1520-0442(2003)016​<0571:BPOASF>2.0.CO;2.

Gregg, M.C., E.A. D’Asaro, J.J. Riley, and E. Kunze. 2019. Mixing efficiency in the ocean. Annual Review of Marine Science 10:443–473, https://doi.org/​10.1146/annurev-marine-121916-063643.

Hasegawa, D., H. Yamazaki, R.G. Lueck, and L. Seuront. 2004. How islands stir and fertilize the upper ocean. Geophysical Research Letters 31, L16303, https://doi.org/10.1029/2004GL020143.

Hasegawa, D., M.R. Lewis, and A. Gangopadhyay. 2009. How islands cause phytoplankton to bloom in their wakes. Geophysical Research Letters 36(20), https://doi.org/​10.1029/​2009GL039743.

Ijichi, T., and T. Hibiya. 2018. Observed variations in turbulent mixing efficiency in the deep ocean. Journal of Physical Oceanography 48:1,815–1,830, https://doi.org/10.1175/JPO-D-17-0275.1.

Johnston, T.M.S., J.A. MacKinnon, P.L. Colin, P.J. Haley Jr., P.F.J. Lermusiaux, A.J. Lucas, M.A. Merrifield, S.T. Merrifield, C. Mirabito, J.D. Nash, and others. 2019. Energy and momentum lost to wake eddies and lee waves generated by the North Equatorial Current and tidal flows at Peleliu, Palau. Oceanography 32(4):110–125, https://doi.org/10.5670/oceanog.2019.417.

Large, W.G., J.C. McWilliams, and S.C. Doney. 1994. Oceanic vertical mixing: A review and a model with a nonlocal boundary layer parameterization. Reviews of Geophysics 32:363–403, https://doi.org/​10.1029/94RG01872.

Lombardo, C., and M.C. Gregg. 1989. Similarity scaling of viscous and thermal dissipation in a convecting surface boundary layer. Journal of Geophysical Research 94(C5):6,273–6,284, https://doi.org/​10.1029/JC094iC05p06273.

MacKinnon, J.A., M.H. Alford, G. Voet, K. Zeiden, T.M.S. Johnston, M. Siegelman, S. Merrifield, and M. Merrifield. 2019. Eddy wake generation from broadband currents near Palau. Journal of Geophysical Research 124:4,891–4,903, https://doi.org/​10.1029/2019JC014945.

Merrifield, S.T., P.L. Colin, T. Cook, C. Garcia-Moreno, J.A. MacKinnon, M. Otero, T.A. Schramek, M. Siegelman, H.L. Simmons, and E.J. Terrill. 2019. Island wakes observed from high-frequency current mapping radar. Oceanography 32(4):92–101, https://doi.org/10.5670/oceanog.2019.415.

Merrifield, S.T., T.A. Schramek, S. Celona, A.B. Villas Bôas, P.L. Colin, and E.J. Terrill. 2019. Typhoon-forced waves around a western Pacific island nation. Oceanography 32(4):56–65, https://doi.org/​10.5670/​oceanog.2019.411.

Munk, W. 1981. Internal waves and small-scale mixing processes. Pp. 264–290 in Evolution of Physical Oceanography. B.A. Warren and C. Wunsch, eds, MIT Press.

Osborn, T.R. 1980. Estimates of the local rate of vertical diffusion from dissipation measurements. Journal of Physical Oceanography 10(1):83–89, https://doi.org/10.1175/1520-0485(1980)010<0083:​EOTLRO>2.0.CO;2.

Schofield, O., J. Kohut, D. Aragon, L. Creed, J. Graver, C. Haldeman, J. Kerfoot, H. Roarty, C. Jones, D. Webb, and S. Glenn. 2007. Slocum gliders: Robust and ready. Journal of Field Robotics 24(6):473–485, https://doi.org/10.1002/rob.20200.

Schönau, M.C., and D.L. Rudnick. 2015. Glider observations of the North Equatorial Current in the western tropical Pacific. Journal of Geophysical Research 120:3,586–3,605, https://doi.org/​10.1002/2014JC010595.

Simmons, H.L., B.S. Powell, S.T. Merrifield, S.E. Zedler, and P.L. Colin. 2019. Dynamical downscaling of equatorial flow response to Palau. Oceanography 32(4):84–91, https://doi.org/​10.5670/oceanog.2019.414.

St. Laurent, L., and C. Garrett. 2002. The role of internal tides in mixing the deep ocean. Journal of Physical Oceanography 32:2,882–2,899, https://doi.org/10.1175/1520-0485(2002)032​<2882:TROITI>2.0.CO;2.

St. Laurent, L., and H. Simmons. 2006. Estimates of power consumed by mixing in the ocean interior. Journal of Climate 19:4,877–4,890, https://doi.org/​10.1175/JCLI3887.1.

St. Laurent, L., and S. Merrifield. 2017. Measurements of near-surface turbulence and mixing from autonomous ocean gliders. Oceanography 30(2):116–125, https://doi.org/10.5670/oceanog.2017.231.

Thomas, L., A. Tandon, and A. Mahadevan. 2008. Submesoscale ocean processes and dynamics. Pp. 17–38 in Ocean Modeling in an Eddying Regime. M. Hecht and H. Hasume, eds, Geophysical Monograph 177, American Geophysical Union, Washington, DC.

Webb, D.C., P.J. Simonetti, and C.P. Jones. 2001. SLOCUM: An underwater glider propelled by environmental energy. IEEE Journal of Oceanic Engineering 26(4):447–452, https://doi.org/​10.1109/48.972077.

Webb, D.J. 2018. On the role of the North Equatorial Counter Current during a strong El Niño. Ocean Science 14:633–660, https://doi.org/10.5194/os-14-633-2018.

Weller, R.A., and A.J. Pleuddemann. 1996. Observations of the vertical structure of the oceanic boundary layer. Journal of Geophysical Research 101:8,789–8,806, https://doi.org/​10.1029/96JC00206.

Wolk, F., R.G. Lueck, and L. St. Laurent. 2009. Turbulence measurements from a glider. Pp. 1–6 in Marine Technology for Our Future: Global and Local Challenges. MTS/IEEE.

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