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UP: Umweltphysik

UP 1: Hydrosph
äre

UP 1.4: Fachvortrag

Montag, 13. März 2006, 15:00–15:15, A

Gas Exchange Measurements: Transition of the boundary conditions from a flat to a rough water surface. — •Kai Armin Degreif and Bernd Jähne — Interdisziplinäres Zentrum für Wissenschaftliches Rechnen, Im Neuenheimer Feld 368, D-69120 Heidelberg

The oceans can act as a source or sink for climate relevant gases such as carbon dioxide, methane or dimethyl sulphide. Because the hydrodynamics at the free ocean surface is poorly understood, the estimation of total flux rates of those gases has to rely on empiric parameterisation. Laboratory measurements can help to get a better understanding of the gas transfer rates dependence on hydrodynamic and tracer parameters.

The No-dqcontrolled-leakageNo-dq-technique, a novel approach for measurements of time resolved gas transfer rates at the water surface in laboratory experiments is presented. Transfer velocitities are calculated by the temporal change of the air-sided concentrations in an evasion experiment. The high temporal resolution of only a few minutes permits systematic studies of gas exchange rates under different conditions within short measurement cycles. By using UV-spectroscopy, simultaneous concentration measurements of volatile aromatics in the air and water phases verified the results obtained by the presented technique.

Measurements from a small annular facility with carefully cleaned water surfaces show that the transition of the Schmidt number exponent from a flat to a rough water surface begins at unexpected low wind speeds and extends over a wide range of wind speeds. The transition can be modelled by a facet model.