More than two-thirds of the earth’s surface is covered by oceans. As the largest interface between the two most important compartments of the system earth – the ocean and the atmosphere – the ocean surface plays an eminent role. On both sides of it thin viscous, heat and mass boundary layers are formed, in which molecular diffusion is the dominant transport mechanism. The thickness of these layers controls the speed of exchange (transfer velocity) and depends on a multitude of factors and processes that cause near-surface turbulence. They are less than one millimeter in the air. In water it is even thinner, because molecular diffusion in liquids is much lower than in gases. Even after almost thirty years of intensive research on air-water gas transfer no satisfactory physically-based model of gas transfer is available.
Just recently, significant progress could be gained both in simulation and imaging of the small-scale transport processes at the wind-driven water surface undulated by waves. Firstly, Li-Ping Hung could port her DNS code for simulation of small-scale transport processes across the free air-water interface to the IWR Helix parallel computer (figure). Secondly, by a joint effort of many students within the joint DFG graduate college between Darmstadt and Heidelberg University RTG 1114 “Optical Techniques for Measurement of Interfacial Transport Phenomena”, a breakthrough could be achieved in the imaging of concentration fields in the vicinity of the water surface. For the first time, the thickness of the mass boundary layer can be made visible (video) in a large wind-wave facility, the Heidelberg Aeolotron (https://www.youtube.com/watch?v=UN0WLx9Ow9Q).
Our long-term vision is to establish a new approach to joint imaging and simulation for complex transport processes and to solve the problem of high Schmidt number transport processes at a free, wavy and wind-driven water surface, which cannot be solve with simulation alone. In order to achieve this, a large-scale European project will be established within the already existing ASIST network (http://cordis.europa.eu/project/rcn/109617_en.html). This will establish another bridge between the simulation groups and image processing groups at IWR and strongly enhance the collaboration between the IWR and Environmental Sciences.
Name and contact of project responsible(s):
Involved scientists and partners
Dr. F. Friedl (Interdisciplinary Center for Scientific Computing, Heidelberg University)
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