Abstract
A self-contained 200-kHz inverted echo-sounder was deployed at Ocean Station Papa (NE Pacific, 1400 km west of Vancouver Is.) from 1 March to 20 May, 1996. The instrument operated continuously, recording calibrated volume scattering from near-surface bubbles with 3-s and 30-cm resolution. Average surface wind and significant wave height during this period were 7.5 m/s and 2.8 m, respectively. The data show the frequent occurrence of bubbles organized into vertical, plume-like structures, presumably drawn downward within the convergence zones of Langmuir circulation. Significant bubble plume activity (defined as average plume depth >3 m) was observed during 61% of the operating period. Average bubble plume penetrations of up to 15 m were observed, with maximum penetrations up to 25 m. Within the plumes, the backscatter cross section exhibited an exponential decay with depth, with e-folding scale in the range 0.5 to 2.5 m. Some implications of this plume-like structure for high-frequency sonar performance will be discussed.
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