Study on Modelling the Air-Sea Boundary Processes in Unsteady and Non-Uniform Field by Expanding the TOHOKU Wave Model

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Modelling of the air-sea boundary processes in unsteady, non-uniform field is a fundamental task for the elucidation of large-scale air-sea interactions. Elements to be solved for this subject include (1) to elucidate the dependence of drag and other coefficients in Bulk formulas, or the air-flow roughness parameter, Z<@D20@>D2, on the sea state or wind wave conditions in addition to the wind conditions; (2) to include properly the effect of sea-water droplets in quantitative expressions of sea-surface evaporation and the heat exchange; (3) to establish the way of expression of broad-area distribution of air-sea fluxes by incorporating the above two items together with an appropreate wave prediction model. As to the item (1), detailed structure of the local equilibrium, or the relations among wind waves, turbulence, air and water friction velocity, has been elucidated for pure wind waves. By using the local equilibrium concept, applied to data under strong wind and wind-wave conditions in Bass Strait obtained by a Sydney University colleague, a strong support has been given for our earlier proposal of Z<@D20@>D1 = gamma u<@d2*@>d2/sigma<@d2p@>d2, where gamma = 0.025, u<@d2*@>d2 is the air friction velocity, and sigma<@d2p@>d2 the wind-wave spectral peak angular frequency. For item (2), a new formulation has been given for the rate of production and concentration near the sea surface of sea-water droplets from wind-wave surfaces. For item (3), some progress has been made for the application of our TOHOKU Wave Model to more complicated conditions.