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  • Author or Editor: Christopher W. Fairall x
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Gary A. Wick
,
J. Carter Ohlmann
,
Christopher W. Fairall
, and
Andrew T. Jessup

Abstract

The oceanic near-surface temperature profile must be accurately characterized to enable precise determination of air–sea heat exchange and satellite retrievals of sea surface temperature. An improved solar transmission parameterization is integrated into existing models for the oceanic warm layer and cool skin within the Tropical Ocean and Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) bulk flux model to improve the accuracy of predictions of the temperature profile and corresponding heat flux components. Application of the revised bulk flux model to data from 12 diverse cruises demonstrates that the improved parameterization results in significant changes to the predicted cool-skin effect and latent heat fluxes at low wind speeds with high solar radiation due to reduced absorption of solar radiation just below the surface. Daytime skin-layer cooling is predicted to increase by 0.03 K on average but by more than 0.25 K for winds below 1 m s−1 and surface irradiance exceeding 900 W m−2. Predicted changes to the warm-layer correction were smaller but exceeded 0.1 K below 1 m s−1. Average latent and sensible heat fluxes changed by 1 W m−2, but the latent flux decreased by 5 W m−2 near winds of 0.5 m s−1 and surface irradiance of 950 W m−2. Comparison with direct observations of skin-layer cooling demonstrated, in particular, that use of the improved solar transmission model resulted in the reduction of previous systematic overestimates of diurnal skin-layer warming. Similar results can be achieved using a simplified treatment of solar absorption with an appropriate estimate of the fraction of incident solar radiation absorbed within the skin layer.

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Sophia E. Brumer
,
Christopher J. Zappa
,
Ian M. Brooks
,
Hitoshi Tamura
,
Scott M. Brown
,
Byron W. Blomquist
,
Christopher W. Fairall
, and
Alejandro Cifuentes-Lorenzen

Abstract

Concurrent wavefield and turbulent flux measurements acquired during the Southern Ocean (SO) Gas Exchange (GasEx) and the High Wind Speed Gas Exchange Study (HiWinGS) projects permit evaluation of the dependence of the whitecap coverage W on wind speed, wave age, wave steepness, mean square slope, and wind-wave and breaking Reynolds numbers. The W was determined from over 600 high-frequency visible imagery recordings of 20 min each. Wave statistics were computed from in situ and remotely sensed data as well as from a WAVEWATCH III hindcast. The first shipborne estimates of W under sustained 10-m neutral wind speeds U 10N of 25 m s−1 were obtained during HiWinGS. These measurements suggest that W levels off at high wind speed, not exceeding 10% when averaged over 20 min. Combining wind speed and wave height in the form of the wind-wave Reynolds number resulted in closely agreeing models for both datasets, individually and combined. These are also in good agreement with two previous studies. When expressing W in terms of wavefield statistics only or wave age, larger scatter is observed and/or there is little agreement between SO GasEx, HiWinGS, and previously published data. The wind speed–only parameterizations deduced from the SO GasEx and HiWinGS datasets agree closely and capture more of the observed W variability than Reynolds number parameterizations. However, these wind speed–only models do not agree as well with previous studies than the wind-wave Reynolds numbers.

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James B. Edson
,
Venkata Jampana
,
Robert A. Weller
,
Sebastien P. Bigorre
,
Albert J. Plueddemann
,
Christopher W. Fairall
,
Scott D. Miller
,
Larry Mahrt
,
Dean Vickers
, and
Hans Hersbach

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.

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James B. Edson
,
Venkata Jampana
,
Robert A. Weller
,
Sebastien P. Bigorre
,
Albert J. Plueddemann
,
Christopher W. Fairall
,
Scott D. Miller
,
Larry Mahrt
,
Dean Vickers
, and
Hans Hersbach
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