Ambient and transient bubble spectral densities in quiescent seas and under spilling breakers
Ambient and transient bubble spectral densities in quiescent seas and under spilling breakers
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DOI：
10.1029/jc094ic09p12751
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发表时间：
1989-09
影响因子：
--
通讯作者：
H. Medwin;Nigel D. Breitz
中科院分区：
文献类型：
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作者：
H. Medwin;Nigel D. Breitz
最近发表的在海洋表面附近使用激光全息术进行的观测表明，在静止海洋表面3米范围内，10至15微米半径气泡的密度可高达106(每微米半径增量每立方米)，从而支持20年前从声学角度得出的值。累积的证据表明，加州海岸外的这些静止微泡密度与半径范围为10&60微米的−为4和较大气泡的−为2.5成正比。一个经过校准的浮动多频声学谐振器现在已经被用来获得9个半径的气泡谱，范围从30到240微米，在公海破碎的海浪下25厘米。在这个深度，大于60微米的气泡与半径的关系约为−2.5，而较小的气泡密度的变化约为a−4。我们的密度与最近发表的气泡实验室研究很好地一致，使用的是表面摩擦速度U*大致相同的风吹表面下的激光散射。在海洋深度75厘米处，较老的照片得出的密度仅在有限的50至100微米范围内与新数据接近。过去声学结果和光学结果之间的不一致显然是由于一些光学技术无法在困难的海洋环境中识别小气泡。
Recently published observations, using laser holography near the ocean surface, have shown that the densities of 10 to 15 micron radius bubbles can be as high as 106 (per cubic meter per micron radius increment) within 3 m of the surface of quiescent seas, thereby supporting the acoustically derived values of two decades ago. The accumulated evidence suggests that these quiescent microbubble densities off the coast of California are proportional to a−4 for radius range 10 < a < 60 microns and a−2.5 for larger bubbles. A calibrated, floating, multi-frequency, acoustical resonator has now been used to obtain the bubble spectrum for 9 radii from 30 to 240 microns, 25 cm under breaking waves in the open sea. At this depth, bubbles larger than 60 microns have a radius dependence approximately a−2.5 and smaller bubble densities vary approximately as a a−4. Our densities are in good agreement with recently published laboratory studies of bubbles, using laser scattering under wind-blown surfaces with about the same surface frictional velocity U*. Older, photographically derived densities at ocean depth 75 cm are close to the new data only over the limited range 50 to 100 microns. Past inconsistencies between acoustical results and optical results were apparently due to an inability of some optical techniques to identify small bubbles in the difficult ocean environment.