Laboratory experiments on wind-wave breaking dynamics and the associated drops, bubbles, and underwater turbulence

Breaking waves influence the transfer of mass and momentum at the air-sea interface through air bubble entrainment and droplet production, which link the ocean and the atmosphere and affect the climate. To improve understanding of how wind and wave conditions affect entrainment and spray generation, an experiment was conducted at the University of Delaware Air-Sea Interaction Laboratory. Waves were produced by combining wind forcing at free-stream velocities of 9.7, 10.7, and 11.7 m/s with mechanically-generated waves with central frequencies of 1.0, 1.2, 1.4, 1.6, and 1.8 Hz and sidebands of ±0.05 Hz, in addition to wind-only forcing. Bubble entrainment in the bulk was captured with planar and stereoscopic shadowgraph techniques, and laser doppler velocimetry was used to characterize the state of underwater turbulence. On the surface, wave gauges and two white-light methods captured the wave state and surface bubbles. Measurements of droplets were made using an in-line holographic system and a shadowgraph technique with a telecentric lens. We discuss this experimental setup and the joint measurements of wind, wave, underwater turbulence, bubble entrainment, and drop generation.