Generation and Propagation of Near-Inertial Waves in a Baroclinic Current on the Tasmanian Shelf

Tamara L. Schlosser Oceans Graduate School and the Ocean Institute, University of Western Australia, Crawley, Western Australia, Australia

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Nicole L. Jones Oceans Graduate School and the Ocean Institute, University of Western Australia, Crawley, Western Australia, Australia

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Cynthia E. Bluteau Institut des Sciences de la Mer, Université du Québec à Rimouski, Rimouski, Quebec, Canada

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Matthew H. Alford Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California

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Gregory N. Ivey Oceans Graduate School and the Ocean Institute, University of Western Australia, Crawley, Western Australia, Australia

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Andrew J. Lucas Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California

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Abstract

Near-inertial waves (NIWs) are often an energetic component of the internal wave field on windy continental shelves. The effect of baroclinic geostrophic currents, which introduce both relative vorticity and baroclinicity, on NIWs is not well understood. Relative vorticity affects the resonant frequency feff, while both relative vorticity and baroclinicity modify the minimum wave frequency of freely propagating waves ωmin. On a windy and narrow shelf, we observed wind-forced oscillations that generated NIWs where feff was less than the Coriolis frequency f. If everywhere feff > f then NIWs were generated where ωmin < f and feff was smallest. The background current not only affected the location of generation, but also the NIWs’ propagation direction. The estimated NIW energy fluxes show that NIWs propagated predominantly toward the equator because ωmin > f on the continental slope for the entire sample period. In addition to being laterally trapped on the shelf, we observed vertically trapped and intensified NIWs that had a frequency ω within the anomalously low-frequency band (i.e., ωmin < ω < feff), which only exists if the baroclinicity is nonzero. We observed two periods when ωmin < f on the shelf, but the relative vorticity was positive (i.e., feff > f) for one of these periods. The process of NIW propagation remained consistent with the local ωmin, and not feff, emphasizing the importance of baroclinicity on the NIW dynamics. We conclude that windy shelves with baroclinic background currents are likely to have energetic NIWs, but the current and seabed will adjust the spatial distribution and energetics of these NIWs.

© 2019 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Tamara Schlosser, tamaralschlosser@gmail.com

Abstract

Near-inertial waves (NIWs) are often an energetic component of the internal wave field on windy continental shelves. The effect of baroclinic geostrophic currents, which introduce both relative vorticity and baroclinicity, on NIWs is not well understood. Relative vorticity affects the resonant frequency feff, while both relative vorticity and baroclinicity modify the minimum wave frequency of freely propagating waves ωmin. On a windy and narrow shelf, we observed wind-forced oscillations that generated NIWs where feff was less than the Coriolis frequency f. If everywhere feff > f then NIWs were generated where ωmin < f and feff was smallest. The background current not only affected the location of generation, but also the NIWs’ propagation direction. The estimated NIW energy fluxes show that NIWs propagated predominantly toward the equator because ωmin > f on the continental slope for the entire sample period. In addition to being laterally trapped on the shelf, we observed vertically trapped and intensified NIWs that had a frequency ω within the anomalously low-frequency band (i.e., ωmin < ω < feff), which only exists if the baroclinicity is nonzero. We observed two periods when ωmin < f on the shelf, but the relative vorticity was positive (i.e., feff > f) for one of these periods. The process of NIW propagation remained consistent with the local ωmin, and not feff, emphasizing the importance of baroclinicity on the NIW dynamics. We conclude that windy shelves with baroclinic background currents are likely to have energetic NIWs, but the current and seabed will adjust the spatial distribution and energetics of these NIWs.

© 2019 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Tamara Schlosser, tamaralschlosser@gmail.com
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  • Alessi, C. A., and Coauthors, 1985: CODE-2: Moored array and large-scale data report. CODE Tech. Rep. 38/WHOI Tech. Rep. 85-35, 234 pp., https://doi.org/10.1575/1912/1641.

    • Crossref
    • Export Citation
  • Alford, M. H., 2003: Redistribution of energy available for ocean mixing by long-range propagation of internal waves. Nature, 423, 159162, https://doi.org/10.1038/nature01628.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Alford, M. H., and M. Whitmont, 2007: Seasonal and spatial variability of near-inertial kinetic energy from historical moored velocity records. J. Phys. Oceanogr., 37, 20222037, https://doi.org/10.1175/JPO3106.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Alford, M. H., J. A. MacKinnon, H. L. Simmons, and J. D. Nash, 2016: Near-inertial internal gravity waves in the ocean. Annu. Rev. Mar. Sci., 8, 95123, https://doi.org/10.1146/annurev-marine-010814-015746.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Baines, P. G., 1982: On internal tide generation models. Deep-Sea Res. 29A, 307338, https://doi.org/10.1016/0198-0149(82)90098-X.

  • Chant, R., 2001: Evolution of near-inertial waves during an upwelling event on the New Jersey inner shelf. J. Phys. Oceanogr., 31, 746764, https://doi.org/10.1175/1520-0485(2001)031<0746:EONIWD>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Chapman, D. C., 1982: Nearly trapped internal edge waves in a geophysical ocean. Deep-Sea Res., 29A, 525533, https://doi.org/10.1016/0198-0149(82)90074-7.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Dale, A. C., J. M. Huthnance, and T. J. Sherwin, 2001: Coastal-trapped waves and tides at near-inertial frequencies. J. Phys. Oceanogr., 31, 29582970, https://doi.org/10.1175/1520-0485(2001)031<2958:CTWATA>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • D’Asaro, E. A., 1985: The energy flux from the wind to near-inertial motions in the surface mixed layer. J. Phys. Oceanogr., 15, 10431059, https://doi.org/10.1175/1520-0485(1985)015<1043:TEFFTW>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • D’Asaro, E. A., 1989: The decay of wind-forced mixed layer inertial oscillations due to the β effect. J. Geophys. Res., 94, 20452056, https://doi.org/10.1029/JC094iC02p02045.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Davies, A. M., and J. Xing, 2005: The effect of a bottom shelf front upon the generation and propagation of near-inertial internal waves in the coastal ocean. J. Phys. Oceanogr., 35, 976990, https://doi.org/10.1175/JPO2732.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Federiuk, J., and J. S. Allen, 1996: Model studies of near-inertial waves in flow over the Oregon continental shelf. J. Phys. Oceanogr., 26, 20532075, https://doi.org/10.1175/1520-0485(1996)026<2053:MSONIW>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Gill, A. E., 1982: Atmosphere-Ocean Dynamics. International Geophysics Series, Vol. 30, Academic Press, 662 pp.

  • Kunze, E., 1985: Near-inertial wave propagation in geostrophic shear. J. Phys. Oceanogr., 15, 544565, https://doi.org/10.1175/1520-0485(1985)015<0544:NIWPIG>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lee, D.-K., and P. P. Niiler, 1998: The inertial chimney: The near-inertial energy drainage from the ocean surface to the deep layer. J. Geophys. Res., 103, 75797591, https://doi.org/10.1029/97JC03200.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lerczak, J. A., M. C. Hendershott, and C. D. Winant, 2001: Observations and modeling of coastal internal waves driven by a diurnal sea breeze. J. Geophys. Res., 106, 19 71519 729, https://doi.org/10.1029/2001JC000811.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lerczak, J. A., C. D. Winant, and M. C. Hendershott, 2003: Observations of the semidiurnal internal tide on the southern California slope and shelf. J. Geophys. Res. Oceans, 108, 3068, https://doi.org/10.1029/2001JC001128.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lilly, J. M., 2017: jLab: A data analysis package for Matlab. Version 1.6.3, http://www.jmlilly.net/jmlsoft.html.

  • Lucas, A. J., G. C. Pitcher, T. A. Probyn, and R. M. Kudela, 2014: The influence of diurnal winds on phytoplankton dynamics in a coastal upwelling system off southwestern Africa. Deep-Sea Res. II, 101, 5062, https://doi.org/10.1016/j.dsr2.2013.01.016.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • MacKinnon, J. A., and M. C. Gregg, 2005: Near-inertial waves on the New England Shelf: The role of evolving stratification, turbulent dissipation, and bottom drag. J. Phys. Oceanogr., 35, 24082424, https://doi.org/10.1175/JPO2822.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Mooers, C. N. K., 1975: Several effects of a baroclinic current on the cross-stream propagation of inertial-internal waves. Geophys. Fluid Dyn., 6, 245275, https://doi.org/10.1080/03091927509365797.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Oliver, E. C. J., M. Herzfeld, and N. J. Holbrook, 2016: Modelling the shelf circulation off eastern Tasmania. Cont. Shelf Res., 130, 1433, https://doi.org/10.1016/j.csr.2016.10.005.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Pettigrew, N. R., 1981: The dynamics and kinematics of the coastal boundary layer off Long Island. Ph.D. thesis, Massachusetts Institute of Technology, 262 pp.

    • Crossref
    • Export Citation
  • Pinkel, R., M. A. Goldin, J. A. Smith, O. M. Sun, A. A. Aja, M. N. Bui, and T. Hughen, 2011: The Wirewalker: A vertically profiling instrument carrier powered by ocean waves. J. Atmos. Oceanic Technol., 28, 426435, https://doi.org/10.1175/2010JTECHO805.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Pinkel, R., and Coauthors, 2015: Breaking internal tides keep the ocean in balance. Eos, Trans. Amer. Geophys. Union, 96, https://doi.org/10.1029/2015EO039555.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Pollard, R., 1970: On the generation by winds of inertial waves in the ocean. Deep-Sea Res. Oceanogr. Abstr., 17, 795812, https://doi.org/10.1016/0011-7471(70)90042-2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Rayson, M. D., G. N. Ivey, N. L. Jones, R. J. Lowe, G. W. Wake, and J. D. McConochie, 2015: Near-inertial ocean response to tropical cyclone forcing on the Australian North-West Shelf. J. Geophys. Res. Oceans, 120, 77227751, https://doi.org/10.1002/2015JC010868.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Ridgway, K. R., 2007: Long-term trend and decadal variability of the southward penetration of the East Australian Current. Geophys. Res. Lett., 34, L13613, https://doi.org/10.1029/2007GL030393.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Schlosser, T. L., N. L. Jones, R. C. Musgrave, C. E. Bluteau, G. N. Ivey, and A. J. Lucas, 2019: Observations of diurnal coastal-trapped waves with a thermocline-intensified velocity field. J. Phys. Oceanogr., 49, 19731994, https://doi.org/10.1175/JPO-D-18-0194.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Shearman, R. K., 2005: Observations of near-inertial current variability on the New England shelf. J. Geophys. Res., 110, C02012, https://doi.org/10.1029/2004JC002341.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Smith, S. D., 1988: Coefficients for sea surface wind stress, heat flux, and wind profiles as a function of wind speed and temperature. J. Geophys. Res., 93, 15 46715 472, https://doi.org/10.1029/JC093iC12p15467.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Spigel, R. H., and J. Imberger, 1980: The classification of mixed-layer dynamics of lakes of small to medium size. J. Phys. Oceanogr., 10, 11041121, https://doi.org/10.1175/1520-0485(1980)010<1104:TCOMLD>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Tort, M., and K. B. Winters, 2018: Poleward propagation of near-inertial waves induced by fluctuating winds over a baroclinically unstable zonal jet. J. Fluid Mech., 834, 510530, https://doi.org/10.1017/jfm.2017.698.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • van der Lee, E. M., and L. Umlauf, 2011: Internal wave mixing in the Baltic Sea: Near-inertial waves in the absence of tides. J. Geophys. Res., 116, C10016, https://doi.org/10.1029/2011JC007072.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Weller, R. A., 1982: The relation of near-inertial motions observed in the mixed layer during the JASIN (1978) experiment to the local wind stress and to the quasi-geostrophic flow field. J. Phys. Oceanogr., 12, 11221136, https://doi.org/10.1175/1520-0485(1982)012<1122:TRONIM>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Whitt, D. B., and L. N. Thomas, 2013: Near-inertial waves in strongly baroclinic currents. J. Phys. Oceanogr., 43, 706725, https://doi.org/10.1175/JPO-D-12-0132.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Whitt, D. B., and L. N. Thomas, 2015: Resonant generation and energetics of wind-forced near-inertial motions in a geostrophic flow. J. Phys. Oceanogr., 45, 181208, https://doi.org/10.1175/JPO-D-14-0168.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Wunsch, C., 1969: Progressive internal waves on slopes. J. Fluid Mech., 35, 131144, https://doi.org/10.1017/S0022112069001005.

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