Ocean bubbles under high wind conditions - Part 1: Bubble distribution and development
Ocean bubbles under high wind conditions - Part 1: Bubble distribution and development
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DOI：
10.5194/os-18-565-2022
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发表时间：
2022-05-03
期刊：
影响因子：
3.2
通讯作者：
Blomquist, Byron
中科院分区：
文献类型：
--
作者：
Czerski, Helen;Brooks, Ian M.;Blomquist, Byron
由于破波产生的气泡对海气传输、气溶胶产生以及海洋上层光学和声学的影响，因此具有相当大的科学意义。然而，对产生更深气泡羽流（延伸到海洋表面以下2-10米）的过程及其对海气交换的意义仍然缺乏详细的了解。在这里，我们介绍了2013年在北大西洋进行的HiWinGS探险的气泡测量结果，这些测量结果是在风速为10-27 m s（-1）的几场风暴中收集的。一套仪器被用来测量气泡从一个自定向的自由浮动的柱形浮标：一个专门的气泡相机，声学谐振器，和一个向上指向的声纳。本文的重点是气泡空隙率和羽流结构。结果是一致的存在一个不均匀的浅气泡层占据的顶部1-2米的海洋，这是定期补充破碎波，和更深的羽流，只形成从浅层的朗缪尔环流的收敛区。这些平流事件并不直接连接到表面破碎。在2 m深度处的空隙率分布显示，即使在最高风速下，空隙率也在10（-4.5）处出现急剧截止，这意味着存在限制接近表面的空隙率的机制。在风速为16 m/s（-1）或风浪雷诺数为R-Hw = 2 x 10（6）的情况下，2 m深度处的空隙率概率分布在所有条件下都非常相似，但在两个阈值以上显著增加。在风的上升和下降期间，空隙率有显着不同，但与波龄没有区别。有一个复杂的近地表流动结构，由于朗缪尔环流，斯托克斯漂移，风引起的电流剪切，影响顶部几米内的气泡的空间分布。我们没有看到泡沫缓慢溶解的证据，因为泡沫被向下携带，这意味着崩溃是更可能的终止过程。我们的结论是，浅和深气泡层需要同时进行研究，将它们与海洋顶部几米处的三维流动模式联系起来。关于深气泡羽流对海气输送的贡献程度，仍有许多悬而未决的问题。一篇配套论文（Czerski等人，2022）解决了观察到的气泡尺寸分布和负责它们的过程。
The bubbles generated by breaking waves are of considerable scientific interest due to their influence on air- sea gas transfer, aerosol production, and upper ocean optics and acoustics. However, a detailed understanding of the processes creating deeper bubble plumes (extending 2-10 m below the ocean surface) and their significance for air-sea gas exchange is still lacking. Here, we present bubble measurements from the HiWinGS expedition in the North Atlantic in 2013, collected during several storms with wind speeds of 10-27 m s(-1). A suite of instruments was used to measure bubbles from a self-orienting free-floating spar buoy: a specialised bubble camera, acoustical resonators, and an upward-pointing sonar. The focus in this paper is on bubble void fractions and plume structure. The results are consistent with the presence of a heterogeneous shallow bubble layer occupying the top 1-2 m of the ocean, which is regularly replenished by breaking waves, and deeper plumes which are only formed from the shallow layer at the convergence zones of Langmuir circulation. These advection events are not directly connected to surface breaking. The void fraction distributions at 2 m depth show a sharp cut-off at a void fraction of 10(-4.5) even in the highest winds, implying the existence of mechanisms limiting the void fractions close to the surface. Below wind speeds of 16 m s(-1) or a wind-wave Reynolds number of R-Hw = 2 x 10(6) , the probability distribution of void fraction at 2 m depth is very similar in all conditions but increases significantly above either threshold. Void fractions are significantly different during periods of rising and falling winds, but there is no distinction with wave age. There is a complex near-surface flow structure due to Langmuir circulation, Stokes drift, and wind-induced current shear which influences the spatial distribution of bubbles within the top few metres. We do not see evidence for slow bubble dissolution as bubbles are carried downwards, implying that collapse is the more likely termination process. We conclude that the shallow and deeper bubble layers need to be studied simultaneously to link them to the 3D flow patterns in the top few metres of the ocean. Many open questions remain about the extent to which deep bubble plumes contribute to air-sea gas transfer. A companion paper (Czerski et al., 2022) addresses the observed bubble size distributions and the processes responsible for them.