Heidelberg 2015 – scientific programme
UP 16.3: Invited Talk
Friday, March 27, 2015, 11:45–12:15, G/gHS
Air-Sea Gas Exchange: from Empiric Wind Speed Relations to Regimes and Ranges — •Bernd Jähne — Institut für Umweltphysik, Universität Heidelberg — HCI, Universität Heidelberg
Even after more than thirty years of intensive research on air-water gas transfer (the 1st symposium on Gas Transfer at Water Surfaces took place in 1983), no satisfactory physically-based model of gas transfer is available. Consequently, semi-empirical relationships between the gas transfer velocity k and wind speed at 10 m height, U10, are still state-of-the-art — and (too) many of them are available.
However, measured transfer velocities show significant deviations from a such a simple relationship. This variability is obviously caused by different conditions at the water surface at the same wind speed such as atmospheric stability, water temperature, different degrees of contamination by surface active material, and the sea state — but a comprehensive model will need further years of research.
Given this unsatisfactory situation, a better alternative to empirical wind speed relations is proposed: the definition of upper and lower limits in different wind speed regimes both for the gas transfer velocity and its dependency on the Schmidt number. This approach is possible by a combined analysis including theoretical considerations and available laboratory and field data. In this way, modelers get clear evidence about the range of possible gas transfer velocities in different wind speed ranges.