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  • Author or Editor: R. A. Antonia x
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A. J. Chambers
and
R. A. Antonia

Abstract

The influence of surface waves on the Reynolds shear stress and the heat flux, measured in the atmospheric surface layer ∼5 m above the ocean, is discussed using the method of Lu and Willmarth (1973). During the observational period, the phase velocity C associated with the dominant wave frequency is 33–80 times larger than the friction velocity u *. When contributions to the momentum flux − uw are sorted out into the four quadrants of the (u,w) plane, the contribution from the interaction quadrants (u>0, w>0; u<0, w<0) increases as C/u * increases. The contributions to the heat flux are not appreciably affected by C/u *. While the probability that sweep and ejection quadrants associated with instantaneous shear-stress and heat-flux fluctuations occur at the same time is large and approximately independent of C/u *, the probability of simultaneous occurrence of interaction events increases as C/u * increases. The period between ejection events also increases with C/u *.

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R. A. Antonia
and
A. J. Chambers

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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R. A. Antonia
,
A. J. Chambers
,
S. Rajagopalan
,
K. R. Sreenivasan
, and
C. A. Friehe

Abstract

Measurements of turbulent momentum, heat and moisture fluxes have been made in Bass Strait from a stable platform, at a height of approximately 5 m above water. Direct measurements of these fluxes are compared with estimates obtained from spectra of velocity, temperature and humidity fluctuations with the use of the inertial dissipation technique. Directly measured momentum and moisture flux values are in reasonable agreement with inertial dissipation values. The sensible heal flux obtained by the inertial dissipation technique is about twice as large as the directly measured heat flux. The dependence on wind speed of bulk transfer coefficients of momentum, heat and moisture and of variances of velocity and scalar fluctuations is discussed and compared with available data.

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