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| Titel |
Directional short wind wave spectra derived from the sea surface photography |
| VerfasserIn |
Vladimir Dulov, Maria Yurovskaya, Bertrand Chapron, Vladimir Kudryavtsev |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250088230
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| Publikation (Nr.) |
 EGU/EGU2014-2317.pdf |
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| Zusammenfassung |
| New field measurements of 2-D wave number short wind wave spectra in the wavelength
range from few millimeters to few decimeters are reported and discussed. The measurement
method proposed by [Kosnik and Dulov, 2011] is based on stereophotography and image
brightness contrast processing. The method strongly builds on the brightness cross-spectral
analysis to reduce the noise within this short wave gravity and capillary range. Field
measurements of wind wave spectra are still rare, and the reported data thus provide valuable
information to bring new evidences on the 2-D spectral distribution of short wind waves in
the wavelength range from decimeters to millimeters.
As found, the folded spectra of decimeter waves are very weakly dependent on the wind
speed and its direction. Wind speed and direction sensitivity only starts to appear in the short
wavelength range, more precisely in the vicinity of the wave number 100 rad/m, where the
wind exponent grows from 0.5 to 1.5–2.5 at 800 rad/m, and angular anisotropy parameter
introduced by [Elfouhaily et al., 1997] amounts the value of 0.5. These aspects are consistent
with other previously reported optical and radar data. For the latter, we solely extracted the
polarization sensitivity to best isolate the contribution associated to the wave saturation
spectrum around the Bragg resonant wave number. For the former, mean-squared
slope statistics were used to assess the integrated shortscale directional spectral
properties.
As revealed, observed direction spectral distributions are significantly different from
those previously suggested [Elfouhaily et al., 1997; Kudryavtsev et al., 2003, 2005]. On the
basis of these new in situ measurements, we then propose to revise the semiempirical
analytical model of short wind wave spectra developed by [Kudryavtsev et al., 2003, 2005].
In this model the key parameter is exponent n governing the nonlinear dissipation rate as
D ~ Bn+1, where B is saturation spectrum. Accordingly, new additional constraints are used
to refine the dependence of the n on dimensionless wave number to match the inferred wind
exponent data. As appeared, such a constraint is a key to refine the directional spectrum. The
mean saturation spectrum is further adjusted to be consistent with the robust Cox and
Munk [1954] dependence of mean-square slope on wind speed. As developed, the
proposed two-dimensional wave number spectrum is valid over the ultragravity and
capillary large wave numbers, and is analytically amenable to different usage. This
revised model can readily be implemented in other studies (radar scattering, air-sea
interaction issues, etc.), where detailed knowledge of short wind wave spectra is
crucial.
The core support of this work was provided by the mega grant of the Russian Federation
Government under grant 11.G34.31.0078, and IFREMER-DVS contracts 2011 2 20712376
and 2012 2 20712805. The research leading to these results has also received funding from
the European Community’s Seventh Framework Programme (FP7/2007–2013) under grant
Agreement 287844 for the project COCONET, the Russian Federal Programme under
contracts N14.B37.21.0619 and N2012-1.2.1–12-000–2007-078 and Ukrainian State
Agency of Science, Innovations and Information under contracts F53/117-2013 and
M/281-2013. Authors gratefully acknowledge continuing support of these foundations. |
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