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| Titel |
Gas transfer under high wind and its dependence on wave breaking and sea state |
| VerfasserIn |
Sophia Brumer, Christopher Zappa, Christopher Fairall, Byron Blomquist, Ian Brooks, Mingxi Yang |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250130662
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| Publikation (Nr.) |
 EGU/EGU2016-10951.pdf |
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| Zusammenfassung |
| Quantifying greenhouse gas fluxes on regional and global scales relies on parameterizations
of the gas transfer velocity K. To first order, K is dictated by wind speed (U) and is typically
parameterized as a non-linear functions of U. There is however a large spread in K predicted
by the traditional parameterizations at high wind speed. This is because a large variety of
environmental forcing and processes (Wind, Currents, Rain, Waves, Breaking, Surfactants,
Fetch) actually influence K and wind speed alone cannot capture the variability of air-water
gas exchange.
At high wind speed especially, breaking waves become a key factor to take into
account when estimating gas fluxes. The High Wind Gas exchange Study (HiWinGS)
presents the unique opportunity to gain new insights on this poorly understood
aspects of air-sea interaction under high winds. The HiWinGS cruise took place in
the North Atlantic during October and November 2013. Wind speeds exceeded
15 m s−1 25% of the time, including 48 hrs with U10 > 20 m s−1. Continuous
measurements of turbulent fluxes of heat, momentum, and gas (CO2, DMS, acetone and
methanol) were taken from the bow of the R/V Knorr. The wave field was sampled
by a wave rider buoy and breaking events were tracked in visible imagery was
acquired from the port and starboard side of the flying bridge during daylight hours at
20Hz.
Taking advantage of the range of physical forcing and wave conditions sampled during
HiWinGS, we test existing parameterizations and explore ways of better constraining K based
on whitecap coverage, sea state and breaking statistics contrasting pure windseas to swell
dominated periods. We distinguish between windseas and swell based on a separation
algorithm applied to directional wave spectra for mixed seas, system alignment is considered
when interpreting results.
The four gases sampled during HiWinGS ranged from being mostly waterside controlled
to almost entirely airside controlled. While bubble-mediated transfer appears to be small for
moderately soluble gases like DMS, the importance of wave breaking turbulence transport
has yet to be determined for all gases regardless of their solubility. This will be addressed by
correlating measured K to estimates of active whitecap fraction (WA) and turbulent kinetic
energy dissipation rate (ε). WA and ε are estimated from moments of the breaking
crest length distribution derived from the imagery, focusing on young seas, when it
is likely that large-scale breaking waves (i.e., whitecapping) will dominate the ε. |
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