Hostname: page-component-8448b6f56d-c4f8m Total loading time: 0 Render date: 2024-04-18T16:06:02.878Z Has data issue: false hasContentIssue false
  • English
  • Français

Langmuir turbulence in shallow water. Part 1. Observations

Published online by Cambridge University Press:  28 March 2007

ANN E. GARGETT  and
JUDITH R. WELLS
ANN E. GARGETT
Affiliation:
Center for Coastal Physical Oceanography, Department of Ocean, Earth and Atmospheric Sciences, Old Dominion University, Norfolk, VA 23529, USA
JUDITH R. WELLS
Affiliation:
Center for Coastal Physical Oceanography, Department of Ocean, Earth and Atmospheric Sciences, Old Dominion University, Norfolk, VA 23529, USA
Get access Rights & Permissions [Opens in a new window]

Abstract

During extended deployment at an ocean observatory off the coast of New Jersey, a bottom-mounted five-beam acoustic Doppler current profiler measured large-scale velocity structures that we interpret as Langmuir circulations filling the entire water column. These circulations are the large-eddy structures of wind-wave-driven turbulent flows that occur episodically when a shallow water column experiences prolonged strong wind forcing. Many observational characteristics agree with former descriptions of Langmuir circulations in deep water. The three-dimensional velocity field reveals quasi-organized structures consisting of pairs of surface-intensified counter-rotating vortices, aligned approximately downwind. Maximum downward velocities are stronger than upward velocities, and the downwelling region of each cell, defined as a pair of vortices, is narrower than the upwelling region. Maximum downward vertical velocity occurs at or above mid-depth, and scales approximately with wind speed. The estimated crosswind scale of cells is roughly 3–6 times their vertical scale, set under these conditions by water depth. The long axis of the cells appears to lie at an angle ∼10°–20° to the right of the wind. A major difference from deep-water observations is strong near-bottom intensification of the downwind ‘jets’ found typically centred over downwelling regions. Accessible observational features such as cell morphology and profiles of mean velocities, turbulent velocity variances, and shear stress components are compared with the results of associated large-eddy simulations (reported in Part 2) of shallow water flows driven by surface stress and the Craik–Leibovich vortex forcing generally used to represent generation of Langmuir cells. A particularly sensitive diagnostic for identification of Langmuir circulations as the energy-containing eddies of the turbulent flow is the depth trajectory of invariants of the turbulent stress tensor, plotted in the Lumley ‘triangle’ corresponding to realizable turbulent flows. When Langmuir structures are present in the observations, the Lumley map is distinctly different from that of surface-stress-driven Couette flow, again in agreement with the large-eddy simulations (LES). Unlike the LES, observed velocity fields contain two distinct and significant scales of variability, documented by wavelet analysis of observational records of vertical velocity. Variability with periods of many minutes is that expected from Langmuir cells drifting past the instrument at the slowly time-varying crosswind velocity. Shorter period variability, of the order of 1–2 min, has roughly the observed periodicity of surface wave groups, suggesting a connection with the wave groups themselves and/or the wave breaking associated with them in high wind conditions.

Type
Papers
Information
Journal of Fluid Mechanics , Volume 576 , 10 April 2007 , pp. 27 - 61
Copyright
Copyright © Cambridge University Press 2007

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFERENCES

Assaf, G., Gerard, R. & Gordon, A. L. 1971 Some mechanisms of oceanic mixing revealed in aerial photographs. J. Geophys. Res. 76, 6550–6572.CrossRefGoogle Scholar
Checkley, D. M., Raman, S., Maillet, G. L. & Mason, K. M. 1988 Winter storm effects on the spawning and larval drift of a pelagic fish. Nature 335, 346–348.CrossRefGoogle Scholar
Craik, A. D. D. & Leibovich, S. 1976 A rational model for Langmuir circulations. J. Fluid. Mech. 73, 401–426.CrossRefGoogle Scholar
D'Asaro, E. A. 2001. Turbulent vertical kinetic energy in the ocean mixed layer. J. Phys. Oceanogr. 31, 3530–3537.2.0.CO;2>CrossRefGoogle Scholar
Faller, A. J. 1964 The angle of windrows in the ocean. Tellus 16, 363–370.CrossRefGoogle Scholar
Faller, A. J. & Caponi, E. A. 1978 Laboratory studies of wind-driven Langmuir circulation. J. Geophys. Res. 83, 3617–3633.CrossRefGoogle Scholar
Gnanadesikan, A. 1996 Mixing driven by vertically variable forcing: an application to the case of Langmuir Circulation. J. Fluid Mech. 322, 81–107.CrossRefGoogle Scholar
Gargett, A., Wells, J., Tejada-Martínez, A. E. & Grosch, C. E. 2004 Langmuir supercells: a mechanism for sediment resuspension and transport in shallow seas. Science 306, 1925–1928.Google Scholar
Hunter, R. E. & Hill, G. W. 1980 Near-shore current pattern off south Texas: an interpretation from aerial photographs. Remote Sensing Environ. 10, 115–134.CrossRefGoogle Scholar
Kim, J., Moin, P. & Moser, R. 1987 Turbulence statistics in fully developed channel flow at low Reynolds number. J. Fluid Mech. 177, 133–166.CrossRefGoogle Scholar
Kohut, J. T., Glenn, S. M. & Chant, R. J. 2004 Seasonal current variability on the New Jersey inner shelf. J. Geophys. Res. 109, C07S07. doi:10.1029/2003JC001963.Google Scholar
Langmuir, I. 1938 Surface motion of water induced by wind. Science 87, 119–123.CrossRefGoogle ScholarPubMed
Leibovich, S. 1983 The form and dynamics of Langmuir circulations. Annu. Rev. Fluid Mech. 15, 391–427.CrossRefGoogle Scholar
Lenschow, D. H., Mann, J. & Kristensen, L. 1994 How long is long enough when measuring fluxes and other turbulence statistics? J. Atmos. Ocean. Technol. 11, 661–673.2.0.CO;2>CrossRefGoogle Scholar
Li, M. & Garrett, C. 1995 Is Langmuir circulation driven by surface waves or surface cooling? J. Phys. Oceanogr. 25, 64–76.2.0.CO;2>CrossRefGoogle Scholar
Li, M. & Garrett, C. 1997 Mixed layer deepening due to Langmuir circulation. J. Phys. Oceanogr. 27, 121–132.2.0.CO;2>CrossRefGoogle Scholar
Li, M., Garrett, C. & Sykllingstad, E. 2005 A regime diagram for classifying turbulent eddies in the upper ocean. Deep-Sea Res. I 52, 259–278. doi:10.1016/j.dsr.2004.09.004.CrossRefGoogle Scholar
Lohrmann, A., Hackett, B. & Roed, L. P. 1990 High resolution measurements of turbulence, velocity, and stress using a pulse-to-pulse coherent sonar. J. Atmos. Ocean. Tech. 7, 19–37.2.0.CO;2>CrossRefGoogle Scholar
Lumley, J. L. 1978 Computational modelling of turbulent flow. J. Geophys. Res. 88, 123–176.Google Scholar
McWilliams, J. C., Sullivan, P. P. & Moeng, C.-H. 1997 Langmuir turbulence in the ocean. J. Fluid Mech. 334, 1–30.CrossRefGoogle Scholar
Marmorino, G. O., Smith, G. B. & Lindemann, G. J. 2004 Infrared imagery of large-aspect-ratio Langmuir circulation. Contl. Shelf Res. 25, 1–6. doi:10.1016/j.csr.2004.08.002.Google Scholar
Münchow, A. & Chant, R. J. 2000 Kinematics of inner shelf motions during the summer stratified season off New Jersey. J. Phys. Oceanogr. 30, 247–268.Google Scholar
Nezu, I. & Nakagawa, H. 1993 Turbulence in Open Channel Flows}. International Association for Hydraulic Research Monograph Series. Balkema, A. A., Rotterdam.Google Scholar
Plueddemann, A. J., Smith, J. A., Farmer, D. Weller, M., Crawford, R. A., Pinkel, W. R., Vagle, R., , S. & Gnanadesikan, A. 1996 Structure and variability of Langmuir circulation during the surface waves processes program. J. Geophys. Res. 101, 3525–3543.CrossRefGoogle Scholar
Pollard, R. T. 1976 Observations and theories of Langmuir circulations and their role in ocean mixing. In A Voyage of Discovery, George Deacon 70th Anniversary Vol., Deep-Sea Res (Suppl.), pp. 235–251.Google Scholar
Pope, S. B. 2000 Turbulent Flows. Cambridge University Press.CrossRefGoogle Scholar
Skyllingstad, E. D. & Denbo, D. W. 1995 An ocean large-eddy simulation of Langmuir circulations and convection in the surface mixed layer. J. Geophys. Res. 100, 8501–8522.Google Scholar
Smith, J., Pinkel, R. & Weller, R. A. 1987 Velocity structure in the mixed layer during MILDEX. J. Phys. Oceanogr. 17, 425–439.Google Scholar
Smith, J. A. 1992 Observed growth of Langmuir circulation. J. Geophys. Res. 97, 5651–5664.CrossRefGoogle Scholar
Tejada-Martínez, A. & Grosch, C. E. 2007 Langmuir turbulence in shallow water. Part 2. Large-eddy simulations. J Fluid Mech. 576, 63–108.CrossRefGoogle Scholar
Tennekes, H. & Lumley, J. L. 1972 A First Course in Turbulence}. The MIT Press, Cambridge MA.CrossRefGoogle Scholar
Thorpe, S. A. 1992 Bubble clouds and the dynamics of the upper ocean. Q. J. R. Met. Soc. 118, 1–22.CrossRefGoogle Scholar
Thorpe, S. A. 2004 Langmuir circulation. Annu. Rev. Fluid Mech. 36, 55–79.CrossRefGoogle Scholar
Thorpe, S. A. & Hall, A. J. 1983 The characteristics of breaking waves, bubble clouds, and near-surface currents observed using side-scan sonar. Continent. Shelf Res. 1, 353–384.CrossRefGoogle Scholar
Trowbridge, J. H. & Agrawal, Y. C. 1995 Glimpses of a wave boundary layer. J. Geophys. Res. 100, 20 729–20 743.CrossRefGoogle Scholar
Van, S traaten, L. M. J. U. 1950 Periodic patterns of rippled and smooth areas on water surfaces, induced by wind action. Koninklijke Ned. Akad. van Wetenschappen Proc. 53, 1217–1227.Google Scholar
Weller, R. A. & Price, J. F. 1988 Langmuir circulation within the oceanic mixed layer. Deep-Sea Res. 35, 711–747.CrossRefGoogle Scholar
Zedel, L. & Farmer, D. M. 1991 Organized structures in subsurface bubble clouds: Langmuir circulation in the open ocean. J. Geophys. Res. 96, 8889–8900.CrossRefGoogle Scholar