Editorial Type:
Article
Article Type:
Research Article

Can Drake Passage Observations Match Ekman's Classic Theory?

Jeff A. Polton National Oceanography Centre, Liverpool, United Kingdom

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Yueng-Djern Lenn School of Ocean Sciences, Bangor University, Menai Bridge, United Kingdom

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Shane Elipot Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida

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Teresa K. Chereskin Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California

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Janet Sprintall Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California

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Print Publication:
01 Aug 2013
DOI:
https://doi.org/10.1175/JPO-D-13-034.1
Page(s):
1733–1740
Restricted access

Abstract

Ekman's theory of the wind-driven ocean surface boundary layer assumes a constant eddy viscosity and predicts that the current rotates with depth at the same rate as it decays in amplitude. Despite its wide acceptance, Ekman current spirals are difficult to observe. This is primarily because the spirals are small signals that are easily masked by ocean variability and cannot readily be separated from the geostrophic component. This study presents a method for estimating ageostrophic currents from shipboard acoustic Doppler current profiler data in Drake Passage and finds that observations are consistent with Ekman's theory. By taking into account the sampling distributions of wind stress and ageostrophic velocity, the authors find eddy viscosity values in the range of 0.08–0.12 m2 s−1 that reconcile observations with the classic theory in Drake Passage. The eddy viscosity value that most frequently reconciles observations with the classic theory is 0.094 m2 s−1, corresponding to an Ekman depth scale of 39 m.

Denotes Open Access content.

Corresponding author address: J. Polton, NOC, 6 Brownlow Street, Liverpool L3 5DA, United Kingdom. E-mail: jelt@noc.ac.uk

Abstract

Ekman's theory of the wind-driven ocean surface boundary layer assumes a constant eddy viscosity and predicts that the current rotates with depth at the same rate as it decays in amplitude. Despite its wide acceptance, Ekman current spirals are difficult to observe. This is primarily because the spirals are small signals that are easily masked by ocean variability and cannot readily be separated from the geostrophic component. This study presents a method for estimating ageostrophic currents from shipboard acoustic Doppler current profiler data in Drake Passage and finds that observations are consistent with Ekman's theory. By taking into account the sampling distributions of wind stress and ageostrophic velocity, the authors find eddy viscosity values in the range of 0.08–0.12 m2 s−1 that reconcile observations with the classic theory in Drake Passage. The eddy viscosity value that most frequently reconciles observations with the classic theory is 0.094 m2 s−1, corresponding to an Ekman depth scale of 39 m.

Denotes Open Access content.

Corresponding author address: J. Polton, NOC, 6 Brownlow Street, Liverpool L3 5DA, United Kingdom. E-mail: jelt@noc.ac.uk
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  • Atlas, R., R. N. Hoffman, J. Ardizzone, S. M. Leidner, J. C. Jusem, D. K. Smith, and D. Gombos, 2011: A cross-calibrated, multiplatform ocean surface wind velocity product for meteorological and oceanographic applications. Bull. Amer. Meteor. Soc., 92, 157–174.

    • Search Google Scholar
    • Export Citation

  • Chereskin, T. K., 1995: Direct evidence for an Ekman balance in the California Current. J. Geophys. Res., 100 (C9), 18 261–18 269.

  • Chereskin, T. K., and D. Roemmich, 1991: A comparison of measured and wind-derived Ekman transport at 11°N in the Atlantic Ocean. J. Phys. Oceanogr., 21, 869–878.

    • Search Google Scholar
    • Export Citation

  • Ekman, V. W., 1905: On the influence of the Earth's rotation on ocean-currents. Ark. Mat. Astron. Fys.,2, 1–52.

  • Elipot, S., and S. T. Gille, 2009: Ekman layers in the Southern Ocean: Spectral models and observations, vertical viscosity and boundary layer depth. Ocean Sci., 5, 115–139.

    • Search Google Scholar
    • Export Citation

  • Firing, E., J. Hummon, and T. Chereskin, 2012: Improving the quality and accessibility of current profile measurements in the Southern Ocean. Oceanography,25, 164–165, doi:10.5670/oceanog.2012.91.

  • Firing, Y. L., T. K. Chereskin, and M. R. Mazloff, 2011: Vertical structure and transport of the Antarctic Circumpolar Current in Drake Passage from direct velocity observations. J. Geophys. Res., 116, C08015, doi:10.1029/2011JC006999.

    • Search Google Scholar
    • Export Citation

  • Gille, S. T., 2005: Statistical characterization of zonal and meridional wind stress. J. Atmos. Oceanic Technol., 22, 1353–1372.

  • Heinloo, J., and A. Toompuu, 2012: A modification of the classical Ekman model accounting for the Stokes drift and stratification effects. Environ. Fluid Mech., 12, 101–113.

    • Search Google Scholar
    • Export Citation

  • Lenn, Y.-D., and T. K. Chereskin, 2009: Observations of Ekman currents in the Southern Ocean. J. Phys. Oceanogr., 39, 768–779.

  • Lenn, Y.-D., T. K. Chereskin, J. Sprintall, and E. Firing, 2007: Mean jets, mesoscale variability and eddy momentum fluxes in the surface-layer of the Antarctic Circumpolar Current. J. Mar. Res., 65, 27–58.

    • Search Google Scholar
    • Export Citation

  • Lewis, D. M., and S. E. Belcher, 2004: Time-dependent, coupled, Ekman boundary layer solutions incorporating Stokes drift. Dyn. Atmos. Oceans, 37, 313–351.

    • Search Google Scholar
    • Export Citation

  • Madsen, O. S., 1977: A realistic model of the wind-induced Ekman boundary layer. J. Phys. Oceanogr., 7, 248–255.

  • McWilliams, J. C., and J. M. Restrepo, 1999: The wave-driven ocean circulation. J. Phys. Oceanogr., 29, 2523–2540.

  • McWilliams, J. C., and E. Huckle, 2006: Ekman layer rectification. J. Phys. Oceanogr., 36, 1646–1659.

  • McWilliams, J. C., E. Huckle, J.-H. Liang, and P. P. Sullivan, 2012: The wavy Ekman layer: Langmuir circulations, breaking waves, and Reynolds stress. J. Phys. Oceanogr., 42, 1793–1816.

    • Search Google Scholar
    • Export Citation

  • Polton, J. A., D. M. Lewis, and S. E. Belcher, 2005: The role of wave-induced Coriolis–Stokes forcing on the wind-driven mixed layer. J. Phys. Oceanogr., 35, 444–457.

    • Search Google Scholar
    • Export Citation

  • Price, J. F., and M. A. Sundermeyer, 1999: Stratified Ekman layers. J. Geophys. Res., 104 (C9), 20 467–20 494.

  • Price, J. F., R. A. Weller, and R. R. Schudlich, 1987: Wind-driven ocean currents and Ekman transport. Science, 238, 1534–1538.

  • Rudnick, D. L., P. Müller, and D. Henderson, Eds., 2003: Observations of momentum transfer in the upper ocean: Did Ekman get it right? Near-Boundary Processes and Their Parameterization: Proc. 13th ‘Aha Huliko ‘a Hawaiian Winter Workshop, Honolulu, HI, University of Hawai‘i at Mānoa, 163–170.

  • Smith, W. H. F., and D. T. Sandwell, 1997: Global sea floor topography from satellite altimetry and ship depth soundings. Science, 277, 1956–1962, doi:10.1126/science.277.5334.1956.

    • Search Google Scholar
    • Export Citation

  • Sprintall, J., 2003: Seasonal to interannual upper-ocean variability in the Drake Passage. J. Mar. Res., 61, 25–57.

  • Webb, A., and B. Fox-Kemper, 2011: Wave spectral moments and Stokes drift estimation. Ocean Modell., 40, 273–288, doi:10.1016/j.ocemod.2011.08.007.

    • Search Google Scholar
    • Export Citation

  • Wijffels, S., E. Firing, and H. Bryden, 1994: Direct observations of the Ekman balance at 10°N in the Pacific. J. Phys. Oceanogr., 24, 1666–1679.

    • Search Google Scholar
    • Export Citation

  • Yelland, M., and P. K. Taylor, 1996: Wind stress measurements from the open ocean. J. Phys. Oceanogr., 26, 541–558.

  • Zikanov, O., D. N. Slinn, and M. R. Dhanak, 2003: Large-eddy simulations of the wind-induced turbulent Ekman layer. J. Fluid Mech., 495, 343–368.

    • Search Google Scholar
    • Export Citation
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