Heidelberg 2015 – wissenschaftliches Programm
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UP: Fachverband Umweltphysik
UP 16: Meßtechnik
UP 16.6: Vortrag
Freitag, 27. März 2015, 12:45–13:00, G/gHS
High-resolution 2-D fluorescence imaging of gas transfer at a free water surface — •Christine Kräuter1,2, Darya Trofimova1,2, Daniel Kiefhaber1,2, and Bernd Jähne1,2 — 1Institut für Umweltphysik, Heidelberg University, Germany — 2Interdisciplinary Center for Scientific Computing, Heidelberg University, Germany
Results from a first study with a novel 2-D fluorescence imaging technique to visualize gas exchange between air and water are presented. The invasion of ammonia into water leads to an increase in pH (starting from a value of 4), which is visualized by a fluorescent dye. Fluorescence is stimulated with high power LED arrays and observed with a low noise scientific CMOS camera. Thus, it is possible to visualize ammonia concentration differences in a thin layer (< 1 mm) at the water surface. By controlling the flux of ammonia, a fraction of the mass boundary layer at the water surface is controlled. In this way, processes from different depths are observed. In addition to the fluorescence measurements, collocated infrared imagery as well as wave slope measurements are available from an experiment at the large annular Aeolotron wind-wave facility at the Institute of Environmental Physics in Heidelberg. The measurements give a direct insight into the mechanisms of air-sea gas transfer. Langmuir circulations enhance gas transfer but do not change the Schmidt number exponent. With increasing frequency of microscale wave breaking, the Schmidt number exponent gradually changes from 2/3 to 1/2. Surface films significantly suppress the frequency of mircoscale wave breaking.