Wind-Wave-Induced Disturbances in the Marine Surface Layer

R. A. Antonia Department of Mechanical Engineering, University of Newcastle, New South Wales 2308, Australia

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A. J. Chambers Department of Mechanical Engineering, University of Newcastle, New South Wales 2308, Australia

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Abstract

Measurements of velocity and scalar fluctuations were made using a stable platform in Bass Strait at a height of ∼5 m above the mean surface of the ocean. These measurements were obtained over a period of time where the wind velocity increased steadily before reaching an approximately constant value that was maintained for a duration of ∼10 h. During the initial period of the experiment, induced wave fluctuations, centered about the dominant wave frequency, are observed an spectra of the longitudinal u and vertical w velocity fluctuations, and on the uw cross spectrum. The cross spectrum indicates a relatively important transfer of momentum in the direction sea to air, at the wave frequency. No measurable wave influence is detected on either temperature θ or humidity q spectra, but wθ and wq cross spectra are either negligible or show a change of sign at the wave frequency. Although the effect on w persists, wave-induced disturbances on the cross spectra are small enough to be neglected when the ratio of wave phase speed to friction velocity becomes smaller than ∼40.

Abstract

Measurements of velocity and scalar fluctuations were made using a stable platform in Bass Strait at a height of ∼5 m above the mean surface of the ocean. These measurements were obtained over a period of time where the wind velocity increased steadily before reaching an approximately constant value that was maintained for a duration of ∼10 h. During the initial period of the experiment, induced wave fluctuations, centered about the dominant wave frequency, are observed an spectra of the longitudinal u and vertical w velocity fluctuations, and on the uw cross spectrum. The cross spectrum indicates a relatively important transfer of momentum in the direction sea to air, at the wave frequency. No measurable wave influence is detected on either temperature θ or humidity q spectra, but wθ and wq cross spectra are either negligible or show a change of sign at the wave frequency. Although the effect on w persists, wave-induced disturbances on the cross spectra are small enough to be neglected when the ratio of wave phase speed to friction velocity becomes smaller than ∼40.

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