Structure of the airflow above surface gravity waves

Abstract eng:
The exchanges of momentum and scalars between the atmosphere and the oceans are influenced by the small-scale dynamics at the wavy air-sea interface. We present 2D PIV measurements of the kinematics in the airflow as low as 100 ,am above the water surface for different wind-wave conditions (wave ages Op /usr between 1.4 and 66.7). Laboratory data were obtained at University of Delaware’s (42-m long) wind-wave-current facility, using a multi-camera multi-laser setup that combines PIV with laser induced fluorescence. Field PIV measurements are also reported. We observe coherent turbulent structures in the airflow, including ejections of low velocity fluid away from the surface and downward sweeps of higher velocity fluid. Wave-phase-resolved quadrant analysis suggests that these events are modulated by the waves. Airflow separation occurs past young wave crests (Op/114* < 3.7), producing intense phase-locked turbulence. When Op /usr = 6.5, the mean wave-coherent airflow is qualitatively consistent with linear critical layer theory.

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