Abstract
Abstract. A comparative study of simultaneous heat and gas exchange measurements was performed in the large annular Heidelberg Air–Sea Interaction Facility, the Aeolotron, under homogeneous water surface conditions. The use of two gas tracers, N2O and C2HF5, resulted not only in gas transfer velocities, but also in the measurement of the Schmidt number exponent n with a precision of ±0.025. The original controlled flux, or active thermographic, technique proposed by Jähne et al. (1989) was applied by heating a large patch at the water surface to measure heat transfer velocities. Heating a large patch, the active thermography technique is laterally homogeneous, and problems of lateral transport effects are avoided. Using the measured Schmidt number exponents, the ratio of the scaled heat transfer velocities to the measured gas transfer velocities is 1.046 ± 0.040, a good agreement within the limits of experimental uncertainties. This indicates the possibility to scale heat transfer velocities measured by active thermography to gas transfer velocities, provided that the Schmidt number exponent is known and that the heated patch is large enough to reach the thermal equilibrium.
Highlights
In 1989 Jähne et al (1989) proposed to use heat as a proxy tracer for gas transfer velocities, called the “controlled flux technique” (CFT)
A comparative study of simultaneous heat and gas exchange measurements was performed in the large annular Heidelberg Air–Sea Interaction Facility, the Aeolotron, under homogeneous water surface conditions
Using the measured Schmidt number exponents, the ratio of the scaled heat transfer velocities to the measured gas transfer velocities is 1.046 ± 0.040, a good agreement within the limits of experimental uncertainties. This indicates the possibility to scale heat transfer velocities measured by active thermography to gas transfer velocities, provided that the Schmidt number exponent is known and that the heated patch is large enough to reach the thermal equilibrium
Summary
In 1989 Jähne et al (1989) proposed to use heat as a proxy tracer for gas transfer velocities, called the “controlled flux technique” (CFT). Haußecker et al (1995) developed a method based on a surface renewal model to track the decay of a small heated spot and applied this technique during the Office of Naval Research (ONR) Marine Boundary Layer Accelerated Research Initiative (MBL ARI) cruise This modification was not verified by independent laboratory measurements by directly comparing gas transfer and heat transfer velocities. By heating a large patch, the active thermography technique is laterally homogeneous – provided the patch is large enough – and all problems with lateral transport effects are avoided This investigation aims to answer the question of whether it is possible to scale heat transfer measurements performed with the CFT to gas transfer measurements without any model assumptions, provided the Schmidt number exponent n is known
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