Field measurements were carried out in the Tanabe bay by StUPA (Structure of Upper Ocean and Atmospheric Mixing) project in order to clarify structures in the upper ocean and the atmospheric surface layer. In this study the most important wave scale for the momentum transfer in the atmospheric surface layer over the bay with mixed states of developing wind-waves and swells is investigated. Momentum fluxes estimated by six empirical formulae for the drag coefficient and the roughness height with various wave scales are compared with measured ones. The results show that the saturation rate of wind-waves is most important index for the momentum transfer in the bay and there is a clear relationship between the drag coefficient and the saturation rate.
