| In recent years, air flow separation over the waves has received much attention due to its importance in the parameterization of the exchanges of various fluxes (heat, gas, momentum) between ocean and atmosphere. Despite of the numerous experimental (Banner & Melville, 1976; Kawai, 1982; Kawamura & Toba, 1988; Banner, 1990; Reul et al., 1999) and computational (Sullivan, 2000; Shen et al., 2003) studies, the understanding of the air flow dynamics above the wind generated waves is still rather poor. Most of the experimental studies are based on mechanical waves, in which case the waves are not directly dependent on the wind stress, hence the air flow dynamics near the surface is still unresolved.; The current research mainly focuses on the air flow dynamics within a few millimeters above the wind generated water waves. In this study Particle Image Velocimetry (PIV) is employed in a controlled laboratory setting to study the air flow dynamics over the wind generated waves. We first have tackled one of the most neglected problems of surface detection in the PIV images. We have discussed three different texture based algorithms to automate the process of surface detection.; We employed a robust pyramid base PIV algorithm to estimate the instantaneuos velocity field above the waves from the pair of PIV images. We have shown the presence of air flow separation over wind generated waves from moderate to high wind speeds. We have also found that the air flow separation significantly affects the air flow dynamics.; In this study, the surface following ensemble averages of the PIV realization has been analyzed. Prior to the current research there has not been any experimental work which could resolve the structures of different physical quantities within the viscous boundary layer. We have shown significant variation of different quantities within that layer, including a direct measurement of the surface viscous stress.; We also designed and implemented a phasemean algorithm over the PIV realizations which could enable us to analyze the phase dependence of the air flow dynamics above the waves. Here we have examined the phase dependence variation of different quantities within the viscous and the buffer layer and have shown well structured phase dependent variations of different quantities with this thin layer. For example, we could see a downward horizontal momentum flux prior to the crest and could note the signatures of upward momentum flux just after the crest. The reporting of such results over the wind generated waves, to the best of authors' knowledge, are one of its kind. |
