Search

A variety of physical mechanisms are jointly responsible for facilitating air‐sea gas transfer through turbulent processes at the atmosphere‐ocean interface. The nature and relative importance of these mechanisms evolves with increasing wind speed. Theoretical and modeling approaches are advancing, but the limited quantity of observational data at high wind speeds hinders the assessment of these efforts. The HiWinGS project successfully measured gas transfer coefficients (k660) with coincident wave statistics under conditions with hourly mean wind speeds up to 24 m s−1and significant wave heights to 8 m. Measurements of k660for carbon dioxide (CO2) and dimethylsulfide (DMS) show an increasing trend with respect to 10 m neutral wind speed (U10N), following a power law relationship of the form: k660CO2∼U10N1.68and k660dms∼U10N1.33. Among seven high wind speed events, CO2transfer responded to the intensity of wave breaking, which depended on both wind speed and sea state in a complex manner, with k660CO2increasing as the wind sea approaches full development. A similar response is not observed for DMS. These results confirm the importance of breaking waves and bubble injection mechanisms in facilitating CO2transfer. A modified version of the Coupled Ocean‐Atmosphere Response Experiment Gas transfer algorithm (COAREG ver. 3.5), incorporating a sea state‐dependent calculation of bubble‐mediated transfer, successfully reproduces the mean trend in observed k660with wind speed for both gases. Significant suppression of gas transfer by large waves was not observed during HiWinGS, in contrast to results from two prior field programs. Large data set of coincident gas transfer and wave measurements under high wind conditionsCOAREG bulk gas transfer model simulates observed gas transfer coefficientsNo evidence for significant suppression of gas transfer in the presence of large waves

AutoFlux is an autonomous system for making direct measurements of the air-sea exchanges of CO2, momentum and heat. Such measurements are usually restricted to short, dedicated air-sea interaction cruises on research ships which last only a few weeks. In contrast, AutoFlux was recently deployed continuously on the RRS Discoveryfor two years and is now currently part of a three year measurement programme on the Norwegian weather ship Polarfront. The instrumentation on Polarfrontalso includes two different wave measurement systems and digital cameras. The various systems are described and initial results presented.

A large dataset of wind stress estimates, covering a wide range of wind speed and stability conditions, was obtained during three cruises of the RRS Discoveryin the Southern Ocean. These data were used by Yelland and Taylor to determine the relationship between 10-m height, neutral stability values for the drag coefficient, and the wind speed, and to devise a new formulation for the nondimensional dissipation function under diabatic conditions. These results have been reevaluated allowing for the airflow distortion caused by the ship. The acceleration and vertical displacement of the flow have been modeled in three dimensions using computational fluid dynamics (CFD). The CFD modeling was tested, first by comparison with wind tunnel measurements on models of two Canadian research ships and second, by analysis of data from four anemometers on the foremast of the RRS Charles Darwin.Originally, the four anemometers gave drag coefficient values that differed by up to 20 from one to another and were all unexpectedly high. The CFD results showed that the airflow had been decelerated by 4–14 and displaced vertically by about 1 m. These effects caused the original drag coefficient results to be overestimated by up to 60. After correcting for flow distortion effects, the results from the different anemometers became consistent, which gave confidence in the quantitative CFD-derived corrections.