Cavity and flow studies of reproducible bubble entrainment events associated with rain.

Rain contributes to the introduction of air into the sea by creating bubbles after impact. Some of these events, particularly from drops 0.8?1.2 mm in diameter, create bubbles reproducibly by a process called regular entrainment. To better understand the mechanics that creates the bubble, kinematic measurements of the cavities formed during regular entrainment events are examined from high-speed motion pictures and are compared with available computational methods. Experimental and numerical results agree with each other on the overall shape of the interface and the occurrence of bubble detachment. Measurements, however, show that the depth of the cavity stagnates before bubble entrapment in a manner that is unseen in the simulation. This stagnation appears to be caused by a counterbalance between surface tension and buoyancy at the bottom of the cavity and to result in the entrapment and eventual detachment of this portion to form the bubble.