Relationship of oceanic whitecap coverage to wind speed and wind history

Callaghan, Adrian H.; Leeuw, G. de; Cohen, Leo H.; O’Dowd, Colin

doi:10.1029/2008gl036165

Cited by 133 publications

(222 citation statements)

References 27 publications

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“…2a). The whitecap vs. wind speed relationship for Knorr_11 is similar in shape to recently published windspeed-based whitecap parameterisations (Callaghan et al, 2008;Schwendeman and Thomson, 2015). At intermediate wind speeds the Knorr_11 whitecap data are lower than the parameterisations (Fig.…”

Section: Whitecapssupporting

confidence: 47%

“…Callaghan et al, 2008;Schwendeman and Thomson, 2015). Bubble-mediated gas transfer is the only viable explanation for the magnitude and wind speed dependence of k w .…”

Section: Discussionmentioning

confidence: 99%

“…Whitecaps were observed during Knorr_11 when wind speeds exceeded 4.5 m s −1 , a typical wind speed threshold for whitecap formation in the open ocean (Callaghan et al, 2008;Schwendeman and Thomson, 2015). Whitecap areal fraction is a strong, non-linear function of wind speed (Fig.…”

Section: Whitecapsmentioning

confidence: 99%

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Estimation of bubble-mediated air–sea gas exchange from concurrent DMS and CO<sub>2</sub> transfer velocities at intermediate–high wind speeds

et al. 2017

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Abstract. Simultaneous air-sea fluxes and concentration differences of dimethylsulfide (DMS) and carbon dioxide (CO 2 ) were measured during a summertime North Atlantic cruise in 2011. This data set reveals significant differences between the gas transfer velocities of these two gases ( k w ) over a range of wind speeds up to 21 m s −1 . These differences occur at and above the approximate wind speed threshold when waves begin breaking. Whitecap fraction (a proxy for bubbles) was also measured and has a positive relationship with k w , consistent with enhanced bubble-mediated transfer of the less soluble CO 2 relative to that of the more soluble DMS. However, the correlation of k w with whitecap fraction is no stronger than with wind speed. Models used to estimate bubble-mediated transfer from in situ whitecap fraction underpredict the observations, particularly at intermediate wind speeds. Examining the differences between gas transfer velocities of gases with different solubilities is a useful way to detect the impact of bubble-mediated exchange. More simultaneous gas transfer measurements of different solubility gases across a wide range of oceanic conditions are needed to understand the factors controlling the magnitude and scaling of bubble-mediated gas exchange.

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Section: Whitecapssupporting

confidence: 47%

“…Callaghan et al, 2008;Schwendeman and Thomson, 2015). Bubble-mediated gas transfer is the only viable explanation for the magnitude and wind speed dependence of k w .…”

Section: Discussionmentioning

confidence: 99%

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Estimation of bubble-mediated air–sea gas exchange from concurrent DMS and CO<sub>2</sub> transfer velocities at intermediate–high wind speeds

et al. 2017

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“…The SEASAW whitecap parameterization is very similar to that of Callaghan et al (2008a) in the wind speed range 8 to 17 m s −1 but drops off faster at lower wind speeds. Both are systematically lower than Monahan and O'Muircheartaigh (1980) as are most of the whitecap fraction estimates observed over the last 10 yr .…”

Section: Whitecap Coveragementioning

confidence: 61%

“…Figure 7 shows the Monahan and O'Muircheartaigh (1980) parameterisation (Eq. 1) along with that of Callaghan et al (2008a) and one derived from the measurements obtained during the SEASAW cruises following the method of Monahan and Lu (1990):…”

Section: Whitecap Coveragementioning

confidence: 99%

Near-surface measurements of sea spray aerosol production over whitecaps in the open ocean

et al. 2013

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Abstract. Simultaneous measurements of near-surface aerosol (0.12 < R < 9.25 µm) and bubble spectra (13 < R < 620 µm) were made during five buoy deployments in the open ocean of the North Atlantic and used to estimate aerosol fluxes per unit area of whitecap. The measurements were made during two cruises as part of the Sea Spray, Gas Flux, and Whitecaps (SEASAW) project, a UK contribution to the international Surface Ocean Lower Atmosphere Study (SOLAS) program. The mean bubble number concentrations for each deployment are in broad agreement with other open ocean spectra and are consistently one to two orders of magnitude lower than surf zone studies. Production fluxes per unit area of whitecap are estimated from the mean aerosol concentration for each buoy deployment. They are found to increase with wind speed, and span the range of values found by previous laboratory and surf-zone studies for particles with radius at 80 % relative humidity, R 80 < 1 µm, but to drop off more rapidly with increasing particle size for larger particles. Estimates of the mean sea spray flux were made by scaling the whitecap production fluxes with in situ estimates of whitecap fraction. The sea spray fluxes are also compared with simultaneous individual eddy covariance flux estimates, and with a sea spray source function derived from them.

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On the variability of whitecap fraction using satellite-based observations

Salisbury

Anguelova

Brooks

2013

J. Geophys. Res. Oceans

101

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[1] Despite decades of effort to accurately quantify whitecap fraction W using in situ photography of the ocean surface, there remains significant scatter in estimates for any given 10 m wind speed (U 10 ). It is believed that the resulting, commonly used, W(U 10 ) parameterizations do not fully account for the true variability in W, by failing to incorporate the impact of the wavefield and other environmental conditions. This paper attests to the variability in whitecap fraction attributed to these additional factors, by analyzing satellitederived W estimates over the globe for a full year. A comparison is made between the wind speed dependence of satellite estimates and three W(U 10 ) relationships formulated from in situ photographic data. The influence of various secondary factors on W is investigated once the dominant wind speed dependence is accounted for. The W retrieval's sensitivity to secondary forcings is dependent upon microwave frequency; at 37 GHz it varies by up to 25% of the mean at a given wind speed, while at 10 GHz it is a maximum of 8%. This results from a frequency-dependent sensitivity to foam depth; at 10 GHz predominantly foam from active breaking waves is detected, while at 37 GHz thin foam in residual whitecaps is also seen. Principal component analysis is used to rank variables by their success in accounting for variability in W. After wind speed, the most important secondary factor that accounts for variability in W is the wavefield. A wind-wave Reynolds number accounts for almost as much variability in W as wind speed.

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Relationship of oceanic whitecap coverage to wind speed and wind history

Cited by 133 publications

References 27 publications

Estimation of bubble-mediated air–sea gas exchange from concurrent DMS and CO<sub>2</sub> transfer velocities at intermediate–high wind speeds

Estimation of bubble-mediated air–sea gas exchange from concurrent DMS and CO<sub>2</sub> transfer velocities at intermediate–high wind speeds

Near-surface measurements of sea spray aerosol production over whitecaps in the open ocean

On the variability of whitecap fraction using satellite-based observations

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Relationship of oceanic whitecap coverage to wind speed and wind history

Cited by 133 publications

References 27 publications

Estimation of bubble-mediated air–sea gas exchange from concurrent DMS and CO&lt;sub&gt;2&lt;/sub&gt; transfer velocities at intermediate–high wind speeds

Estimation of bubble-mediated air–sea gas exchange from concurrent DMS and CO&lt;sub&gt;2&lt;/sub&gt; transfer velocities at intermediate–high wind speeds

Near-surface measurements of sea spray aerosol production over whitecaps in the open ocean

On the variability of whitecap fraction using satellite-based observations

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Resources

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Estimation of bubble-mediated air–sea gas exchange from concurrent DMS and CO<sub>2</sub> transfer velocities at intermediate–high wind speeds

Estimation of bubble-mediated air–sea gas exchange from concurrent DMS and CO<sub>2</sub> transfer velocities at intermediate–high wind speeds