The Relationship Between Breaking Waves And Gas Transfer Velocity

The gas transfer velocity is an important parameter for air-sea gas exchange, butits observations are indeed hard to get. Considering the close relationship between thegas transfer velocity and the wave energy dissipation, we try to express the gas transfervelocity with the dissipation rates of wind waves which are much easier to obtain. Thentwo approaches, concerning respectively buoy observation data and numerical modelingoutput, are used in the calculation of the wave energy dissipation in order to get the gastransfer velocity.Firstly some pre-processings are performed on the buoy data to convert the windmeasurement height to10m, and to remove irregular wave spectra. Thereafter the windwave dissipation rate is calculated following two theorotical models, namely the Hassel-mann’s model and the Phillips’ model. The relationships between the wind wave dissi-pation rate and four other parameters, i.e.,10m wind speed, friction velocity, significantwave height, wind-sea Reynold number, are studied based on the validated data. Com-parisions to literature results show a reasonable acceptance of the calculation here. Of thetwo theoretical models, the Phillips’ model is generally better. Additionally, the wind-seaReynoldnumberturnsouttobethebestparameterofthefourindescribingthewindwavedissipation.Subsequently, the relation between the dissipation rates of wind wave energy andturbulence kinetic energy is derived from dimensional analyses, which is then further ex-tendedtogivetherelationshipbetweenthewindwavedissipationrateandthegastransfervelocity, by means of substituting the1/4power law of the gas transfer velocity and tur-bulent dissipation rate. To determine the one empirical parameter involved, upper andlower limits of the gas transfer velocity found in literatures are used. Hence we explicitlygive a new formula of the gas transfer velocity as a function of the wind wave dissipationrate.Ideal numerical experiments are carried out by using both the WAVEWATCHIII andthe SWAN models, by which the model output wave energy dissipation rate is studied.Comparing with the buoy observation, model output wave energy dissipation rate evolves with wind speed similarly to literature result, but not as well as obervations. Of the twomodels, the WAVEWATCHIII simulates better wave energy dissipation rate.Last but not least, model output wave dissipation rate is utilized to determine the gastransfer velocity as well. The results present that the WAVEWATCHIII simulates a lesssteeper but still reasonable curve of the gas transfer velocity as a function of wind speed,comparing with literature results. Therefore a new numerical modeling approach of thegas transfer velocity is proposed in this study.