On the investigations of micro turbulence at the water surface using infrared imaging

Laboratory studies in the circular Heidelberg wind wave flume and a field study during the 1997 CoOP (Coastal Ocean Processes) experiment in the Atlantic Ocean have been conducted to investigate the relationship between air-sea gas transfer and the micro-scale temperature fluctuations at the water surface. The controlled flux technique (CFT) uses heat as a proxy tracer for gases to measure the gas transfer velocity. The gas transfer rates derived from the experiments agree with the wind speed dependence of the Wanninkhof relationship. Surface renewal events were observed at different spatial scales and at all wind speeds conditions. The investigations suggest that surface renewal is the dominant process in effecting transport across the aqueous boundary layer. Furthermore, infrared image sequences of the water surface allow a detailed study of near surface turbulence with respect to scale and orientation. The micro-scale temperature fluctuations associated with the turbulent transfer at the interface show the same behavior in the field and laboratory. At low wind speed the large scales are dominant, whereas at high wind speeds the small scales dominate the transport at the interface.