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  • 1
    Online Resource
    Online Resource
    American Meteorological Society ; 2008
    In:  Journal of Physical Oceanography Vol. 38, No. 5 ( 2008-05-01), p. 1054-1072
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 38, No. 5 ( 2008-05-01), p. 1054-1072
    Abstract: This study makes direct measurements of turbulent fluxes in the mixed layer in order to close heat and momentum budgets across the air–sea interface and to assess the ability of rigid-boundary turbulence models to predict mean vertical gradients beneath the ocean’s wavy surface. Observations were made at 20 Hz at nominal depths of 2.2 and 1.7 m in ∼16 m of water. A new method is developed to estimate the fluxes and the length scales of dominant flux-carrying eddies from cospectra at frequencies below the wave band. The results are compared to independent estimates of those quantities, with good agreement between the two sets of estimates. The observed temperature gradients were smaller than predicted by standard rigid-boundary closure models, consistent with the suggestion that wave breaking and Langmuir circulation increase turbulent diffusivity in the upper ocean. Similarly, the Monin–Obukhov stability function ϕh was smaller in the authors’ measurements than the stability functions used in rigid-boundary applications of the Monin–Obukhov similarity theory. The dominant horizontal length scales of flux-carrying turbulent eddies were found to be consistent with observations in the bottom boundary layer of the atmosphere and from laboratory experiments in three ways: 1) in statically unstable conditions, the eddy sizes scaled linearly with distance to the boundary; 2) in statically stable conditions, length scales decreased with increasing downward buoyancy flux; and 3) downwind length scales were larger than crosswind length scales.
    Type of Medium: Online Resource
    ISSN: 1520-0485 , 0022-3670
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2008
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 2
    Online Resource
    Online Resource
    American Meteorological Society ; 2014
    In:  Journal of Physical Oceanography Vol. 44, No. 9 ( 2014-09), p. 2590-
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 44, No. 9 ( 2014-09), p. 2590-
    Type of Medium: Online Resource
    ISSN: 0022-3670 , 1520-0485
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2014
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 3
    Online Resource
    Online Resource
    American Meteorological Society ; 2013
    In:  Journal of Physical Oceanography Vol. 43, No. 8 ( 2013-08), p. 1589-1610
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 43, No. 8 ( 2013-08), p. 1589-1610
    Abstract: This study investigates the exchange of momentum between the atmosphere and ocean using data collected from four oceanic field experiments. Direct covariance estimates of momentum fluxes were collected in all four experiments and wind profiles were collected during three of them. The objective of the investigation is to improve parameterizations of the surface roughness and drag coefficient used to estimate the surface stress from bulk formulas. Specifically, the Coupled Ocean–Atmosphere Response Experiment (COARE) 3.0 bulk flux algorithm is refined to create COARE 3.5. Oversea measurements of dimensionless shear are used to investigate the stability function under stable and convective conditions. The behavior of surface roughness is then investigated over a wider range of wind speeds (up to 25 m s −1 ) and wave conditions than have been available from previous oversea field studies. The wind speed dependence of the Charnock coefficient α in the COARE algorithm is modified to , where m = 0.017 m −1 s and b = −0.005. When combined with a parameterization for smooth flow, this formulation gives better agreement with the stress estimates from all of the field programs at all winds speeds with significant improvement for wind speeds over 13 m s −1 . Wave age– and wave slope–dependent parameterizations of the surface roughness are also investigated, but the COARE 3.5 wind speed–dependent formulation matches the observations well without any wave information. The available data provide a simple reason for why wind speed–, wave age–, and wave slope–dependent formulations give similar results—the inverse wave age varies nearly linearly with wind speed in long-fetch conditions for wind speeds up to 25 m s −1 .
    Type of Medium: Online Resource
    ISSN: 0022-3670 , 1520-0485
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2013
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 4
    Online Resource
    Online Resource
    American Meteorological Society ; 2016
    In:  Journal of Atmospheric and Oceanic Technology Vol. 33, No. 5 ( 2016-05), p. 873-890
    In: Journal of Atmospheric and Oceanic Technology, American Meteorological Society, Vol. 33, No. 5 ( 2016-05), p. 873-890
    Abstract: Direct covariance flux (DCF) measurements taken from floating platforms are contaminated by wave-induced platform motions that need to be removed before computation of the turbulent fluxes. Several correction algorithms have been developed and successfully applied in earlier studies from research vessels and, most recently, by the use of moored buoys. The validation of those correction algorithms has so far been limited to short-duration comparisons against other floating platforms. Although these comparisons show in general a good agreement, there is still a lack of a rigorous validation of the method, required to understand the strengths and weaknesses of the existing motion-correction algorithms. This paper attempts to provide such a validation by a comparison of flux estimates from two DCF systems, one mounted on a moored buoy and one on the Air–Sea Interaction Tower (ASIT) at the Martha’s Vineyard Coastal Observatory, Massachusetts. The ASIT was specifically designed to minimize flow distortion over a wide range of wind directions from the open ocean for flux measurements. The flow measurements from the buoy system are corrected for wave-induced platform motions before computation of the turbulent heat and momentum fluxes. Flux estimates and cospectra of the corrected buoy data are found to be in very good agreement with those obtained from the ASIT. The comparison is also used to optimize the filter constants used in the motion-correction algorithm. The quantitative agreement between the buoy data and the ASIT demonstrates that the DCF method is applicable for turbulence measurements from small moving platforms, such as buoys.
    Type of Medium: Online Resource
    ISSN: 0739-0572 , 1520-0426
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2016
    detail.hit.zdb_id: 2021720-1
    detail.hit.zdb_id: 48441-6
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