%0 Generic
%A Schnieders, Jana
%C Heidelberg
%D 2015
%F heidok:18469
%R 10.11588/heidok.00018469
%T Analyzing the footprints of turbulence producing  mechanisms at the free water surface  
%U https://archiv.ub.uni-heidelberg.de/volltextserver/18469/
%X At the free wind-sheared water surface, various turbulence producing mechanisms contribute  significantly to enhanced transfer rates of heat and gas across the air-water boundary. As a result,  surface convergence and divergence form and can be visualized in infrared images of the water  surface. Within this work the footprints of turbulent processes in the surface temperature pattern  are analyzed. Image processing techniques, such as motion estimation and classification, are  adapted and applied to the infrared images of the water surface. Dense flow fields are estimated  without the suppression of surface divergence and up- and down-welling sites are identified.  Data from a range of laboratory facilities is evaluated with a focus on small spatial scales, low  to moderate wind stress and the impact of surfactants on the surface dynamics. In this wind  regime shear induced turbulence, small Langmuir circulations and microscale breaking waves are  identified as the dominant processes that drive heat exchange. The turbulent cell size is suggested  as a characteristic feature of shear and Langmuir turbulence and is related against friction  velocity and wave field. Within this work, a novel method is suggested to assess the impact  of individual processes on the overall heat transfer rate and tested on the measured laboratory  data also with respect to the influence of increasing wind stress and surfactant coverage. The  following key points are found: Shear induced turbulence is a major contributor to enhanced  transfer rates at low wind stress. Its relevance increases if the surface is covered by surfactants  as the onset of waves is delayed. Langmuir circulations play a major role at intermediate wind  stress and cause a significant increase of transfer rates. Surfactants on the water surface delay the  evolution of Langmuir circulation and intensity considerably. Microscale breaking is a dominant  contributor at moderate wind stress and is responsible for approximately 50% and more of the  transfer rate.