Photographic measurements of bubble populations from breaking wind waves at sea

Abstract

A photographic technique was used to measure bubble size spectra at depths of 0.5 – 2.0 m in wind speeds of 2–14 m s −1 . Sampled bubble populations were found to be highly variable with time. The bubble density was found to be a strong function of wind speed, W, varying as W 3.3 and few bubbles were found below 6 m s −1 . For wind speeds between 6 m s −1 and 14 m s −1 the total air volume entrained by bubbles increased as W 4.9 . The state of development of the wave height spectrum also appeared to influence the bubble density. Bubble size spectra varied with radius, r, on average, as r −4 . The more limited oceanic results of previous workers are compatible with these findings.