On the use of the active infrared technique to infer heat and gas transfer velocities at the air‐water free surface

Atmane, Mohamed A.; Asher, William E.; Jessup, Andrew T.

doi:10.1029/2003jc001805

Cited by 42 publications

(64 citation statements)

References 23 publications

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“…[33] An alternative explanation for the mismatch between k G (660) and k H (660) is provided by the results of Atmane et al [2004], who proposed that surface penetration theory [Harriott, 1962] provides a more accurate conceptual model for air-sea exchange than surface renewal theory. Although similar to surface renewal, surface penetration models differ from surface renewal models in that the eddies in the former are not required to completely replace the water surface with water from the bulk phase.…”

Section: Discussionmentioning

confidence: 99%

“…The plots of the normalized average patch temperature versus time in Figure 3 shows that patches during FAIRS and GasEx-01 were imaged for their entire lifetime. The ACFT analysis technique developed by Atmane et al [2004] was used to calculate a temperature decay curve for each patch in a image sequence. These decay curves were then averaged together to form a composite curve for the 300 s (GasEx-01) or 120 s (FAIRS) data record.…”

Section: Acft Experimental Overviewmentioning

confidence: 99%

“…A surface renewal model that assumes Å(t) is given by an exponential distribution is used to generate a simulated decay curve. The simulated curve is fit to the experimentally observed temperature decay curve by adjusting t AVG [Atmane et al, 2004]. Then, since the underlying distribution for Å(t) is an exponential distribution, k H is calculated from equation (2), assuming a = 1.…”

Section: Acft Experimental Overviewmentioning

confidence: 99%

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Oceanic application of the active controlled flux technique for measuring air‐sea transfer velocities of heat and gases

2004

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[1] Detailed understanding of the hydrodynamic mechanisms controlling the air-sea exchange of heat and gas requires a method for rapid measurement of the associated transfer velocities. The active controlled flux technique (ACFT), where the temperature decay of a small patch of water heated by an infrared laser is tracked using an infrared imager, has been proposed as a method for making these fast noninvasive measurements of the heat and gas transfer velocities. Here, we report on ACFT measurements of the transfer velocity of heat, k H , made in the ocean during the Fluxes, Air-sea Interactions and Remote Sensing (FAIRS) experiment (September/October, 2000) and GasEx-01 (January/ February, 2001). The results for k H from both FAIRS and GasEx-01 compare favorably when plotted versus wind speed. However, when scaled to a Schmidt number of 660, the measured k H values were found to be a factor of two larger than gas transfer velocities measured during GasEx-01. The ACFT-derived k H values were combined with direct measurements of the bulk-skin oceanic temperature difference to calculate net air-sea heat fluxes during both experiments. Comparison of these values with heat fluxes determined by direct measurements of the latent, sensible, and radiative heat fluxes showed that the ACFT measurements are a factor of seven larger than the direct measurements. One possible theory explaining both the overprediction of the gas transfer velocities and the scale factor between the measured and calculated net heat fluxes is that air-sea exchange is best described by surface penetration rather than surface renewal.

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Section: Discussionmentioning

confidence: 99%

Section: Acft Experimental Overviewmentioning

confidence: 99%

Section: Acft Experimental Overviewmentioning

confidence: 99%

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Oceanic application of the active controlled flux technique for measuring air‐sea transfer velocities of heat and gases

2004

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“…The passive SR method may underestimate k(600) derived from SF 6 because the resolution of the IR imager used during Bio2 RainX II is large relative to the smallest scale fluctuations, i.e., surface renewal. The SR method may be improved by increasing the resolution of the IR imagery to capture the smallest scales of turbulence affecting the air-water interface, and by implementing the active controlled flux technique [e.g., Jähne and Haußecker, 1998;Asher et al, submitted;Atmane et al, 2004;Zappa et al, 2003Zappa et al, , submitted manuscript, 2004. While the DR method captures the variability of k(600) comparable to the SR method, the SR method may prove to be more powerful since it directly measures surface renewal using IR imagery of the air-water interface.…”

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confidence: 99%

Influence of rain on air‐sea gas exchange: Lessons from a model ocean

Zappa

McGillis

et al. 2004

J. Geophys. Res.

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[1] Rain has been shown to significantly enhance the rate of air-water gas exchange in fresh water environments, and the mechanism behind this enhancement has been studied in laboratory experiments. In the ocean, the effects of rain are complicated by the potential influence of density stratification at the water surface. Since it is difficult to perform controlled rain-induced gas exchange experiments in the open ocean, an SF 6 evasion experiment was conducted in the artificial ocean at Biosphere 2. The measurements show a rapid depletion of SF 6 in the surface layer due to rain enhancement of air-sea gas exchange, and the gas transfer velocity was similar to that predicted from the relationship established from freshwater laboratory experiments. However, because vertical mixing is reduced by stratification, the overall gas flux is lower than that found during freshwater experiments. Physical measurements of various properties of the ocean during the rain events further elucidate the mechanisms behind the observed response. The findings suggest that short, intense rain events accelerate gas exchange in oceanic environments.

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“…Therefore, the Schmidt number effect is not discussed in this paper. Recently, the difference between the diffusivities of gas and heat has raised questions about the effect of penetration depth [Atmane et al, 2004], which led to renewed interest in the random eddy model of Harriott [1962]. An interesting observation from the current work is that the different free-surface boundary conditions for heat and gas also result in disparate behavior of the two, as will be illustrated next, which may add new insight into the physical problem.…”

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confidence: 74%

Surface age of surface renewal in turbulent interfacial transport

Kermani¹,

Shen²

2009

Geophysical Research Letters

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[1] We use direct numerical simulation to study characteristics of interfacial transfer of gas and heat in free-surface turbulence. Using Lagrangian tracing, we are able to directly quantify surface age of surface renewal for the first time. The physical meaning of surface renewal and various representations of surface age, including the use of heat as a proxy, are discussed. Results show that the Higbie penetration theory and the Danckwerts random surface renewal model are inappropriate for gas transfer. [2] Surface renewal is a critical process in turbulent interfacial transport that is important to many applications including sea surface temperature and atmosphere -ocean gas transfer. Scalar transport in the upper ocean is governed by the interplay of molecular diffusion at the sea surface and turbulent mixing underneath. When a surface renewal occurs, fluid is brought from the bulk towards the surface, the scalar is highly mixed, and the gradient of scalar concentration is increased at the surface to enhance interfacial diffusion.[3] An influential model of surface renewal is the penetration theory of Higbie [1935], which stated that the surface is intermittently exposed to turbulent upwelling flows. The turbulent mixing process was considered instant, with the scalar well mixed. After this surface renewal, molecular diffusion was assumed to dominate in the scalar boundary layer till the next surface renewal is generated by the turbulence below. Take gas as an example. Its concentration c is governed by the diffusion equation:2 ). Here D is the molecular diffusivity and z is the vertical coordinate. Subject to the boundary conditions at the surface c(z = 0, t) = c 0 and in the deep region c(z = À1, t) = c bulk , and the initial condition c(z, t = 0) = c bulk , the gas flux at the surface q g obtains asIn the above, the time elapsed since the surface renewal is called the surface age t.[4] Danckwerts [1951] elaborated the penetration theory in his random surface renewal model by assuming that the chance of a surface element being renewed by fresh fluid from the bulk flow is independent of its surface age. Therefore, the probability density function (pdf) of the surface age governed by dp(t)/dt = Às p(t), where p is the pdf and s is the fractional rate of surface elements being renewed (assumed to be constant by Danckwerts), has an exponential solution: p(t) = s exp(Àst). With this pdf, average surface age can be obtained as t = 1/s, and average gas flux at the surface is q g = (c 0 1951] did not account for effects of vertical turbulent advection after t = 0. Near the surface, the advection is in the form of upwelling and can be measured by surface divergency a = @u/@x + @v/@y = À@w/@z (so that w = Àaz), which was considered by Ledwell [1984] and Banerjee [1990]. The relative effects of diffusion and advection can be seen in the upwelling stagnation flow model of Chan and Scriven [1970], in which the advectiondiffusion equation @c/@t = az(@c/@z) + D(@ 2 c/@z 2 ) is solved to obtain the surface gas flux base...

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On the use of the active infrared technique to infer heat and gas transfer velocities at the air‐water free surface

Cited by 42 publications

References 23 publications

Oceanic application of the active controlled flux technique for measuring air‐sea transfer velocities of heat and gases

Oceanic application of the active controlled flux technique for measuring air‐sea transfer velocities of heat and gases

Influence of rain on air‐sea gas exchange: Lessons from a model ocean

Surface age of surface renewal in turbulent interfacial transport

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