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Wave induced wind in the marine boundary layer
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. (meteorologi, awep)
Norwegian meteorological Institute.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. (meteorologi, awep)
Finnish Institute of Marine Research.
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2009 (English)In: Journal of Atmospheric Sciences, ISSN 0022-4928, E-ISSN 1520-0469, Vol. 66, no 8, 2256-2271 p.Article in journal (Refereed) Published
Abstract [en]

Recent field observations and large-eddy simulations have shown that   the impact of fast swell on the marine atmospheric boundary layer  (MABL) might be stronger than previously assumed. For low to moderate   winds blowing in the same direction as the waves, swell propagates   faster than the mean wind. The momentum flux above the sea surface will   then have two major components: the turbulent shear stress, directed   downward, and the swell-induced stress, directed upward. For sufficiently high wave age values, the wave-induced component becomes   increasingly dominant, and the total momentum flux will be directed   into the atmosphere. Recent field measurements have shown that this   upward momentum transfer from the ocean into the atmosphere has a   considerable impact on the surface layer flow dynamics and on the   turbulence structure of the overall MABL. The vertical wind profile   will no longer exhibit a logarithmic shape because an acceleration of   the airflow near the surface will take place, generating a low-level  wave-driven wind maximum (a wind jet). As waves propagate away from   their generation area as swell, some of the wave momentum will be   returned to the atmosphere in the form of wave-driven winds.   A model that qualitatively reproduces the wave-following atmospheric   flow and the wave-generated wind maximum, as seen from measurements, is   proposed. The model assumes a stationary momentum and turbulent kinetic   energy balance and uses the dampening of the waves at the surface to   describe the momentum flux from the waves to the atmosphere. In this   study, simultaneous observations of wind profiles, turbulent fluxes,   and wave spectra during swell events are presented and compared with   the model. In the absence of an established model for the linear   damping ratio during swell conditions, the model is combined with   observations to estimate the wave damping. For the cases in which the   observations showed a pronounced swell signal and almost no wind waves,   the agreement between observed and modeled wind profiles is remarkably   good. The resulting attenuation length is found to be relatively short,   which suggests that the estimated damping ratios are too large. The authors attribute this, at least partly, to processes not accounted for   by the model, such as the existence of an atmospheric background wind. In the model, this extra momentum must be supplied by the waves in   terms of a larger damping ratio.

Place, publisher, year, edition, pages
2009. Vol. 66, no 8, 2256-2271 p.
National Category
Natural Sciences
Research subject
URN: urn:nbn:se:uu:diva-115546DOI: 10.1175/2009JAS3018.1ISI: 000268751700007OAI: oai:DiVA.org:uu-115546DiVA: diva2:295534
Available from: 2010-02-17 Created: 2010-02-17 Last updated: 2013-04-22Bibliographically approved

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Rutgersson, Anna
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