Modeling Bubbly Flows and Bubble-Mediated Gas Transfer in High Wind Conditions

在中等至极端风速下，海洋中的气泡是空气-海洋气体传输的关键组成部分。它们通过提供海洋表面以外的通道来提高气体传输速率。由于表面张力和施加在气泡上的静水压力，气体能够在过饱和条件下溶解。因此，由于海洋表面的脱气和内部通过气泡的溶解，海洋表面是过饱和的。本研究的主要目的是更好地了解强风下气泡和溶解气体的演化过程，并改进气泡介导的气体通量的参数化。本文将验证基于以往观测和理论研究的三个假设：(1)通过气泡的气体溶解对确定飓风下混合层溶解气体浓度很重要；(2)在大风条件下，气泡穿透和气泡介导的气体通量对风速的依赖性较小；(3)气泡增强的二甲基硫化物的有效溶解度和碳酸盐体系的动力学对这些气体的海气通量有重要影响。这些假设将使用耦合-大涡模拟-气泡种群-溶解气体浓度模型进行验证，该模型已被证明可以忠实地再现海洋表面边界层湍流，具有多种气体成分的多种尺寸气泡以及多种气体的溶解浓度之间的同时演化和相互作用。该模型还包括气泡诱导的极性气体DMS有效溶解度的增强和碳酸盐体系的化学反应。该模型将在飓风弗朗西斯（2004）的实际风和波条件下进行，其中湍流、溶解氧和氮的高质量海洋测量将用于衡量模型的真实性，以及稳定的风。知识价值：迄今为止，对地下气泡，特别是在大风条件下的地下气泡的了解还不够充分，气泡对海气总通量的贡献还没有得到充分的约束，尚未包括在任何现有的气候模拟或生物地球化学过程估计中。模拟和数据的综合将以高空间和时间分辨率提供控制气泡和溶解气体的过程的准确描述。这项研究的结果将为气泡分布和气泡介导的气体传递提供基本的理解和基于力学的参数化。它们也将适用于其他反应性和非反应性气体的海气输送。更广泛的影响：强风条件下气泡和海气传输的研究对海洋与大气的物理耦合和全球生物地球化学循环的地球系统的理解有广泛的贡献。大尺度和气候模式对气泡介导的气体通量进行更好的参数化，将显著改善对气候和环境具有重要意义的可溶气体（包括二氧化碳、氧气和二甲基硫化物）的模拟和预算估算。这项研究将提高我们预测未来环境和气候变化的能力，并将为政治和工业决策者在气候和能源等一系列问题上提供更好的科学依据。因此，它具有重要的经济和社会影响。虽然本研究侧重于气泡对海气传输的影响，但更好地描述地下气泡场也有助于更好地表征海洋表面的声光传播，有利于海洋工程界。这个项目将资助一名新的研究者。除了在评审期刊上发表论文外，PI还将积极参加由知名科学团体和学会组织的会议和研讨会，并与海气交换界的其他同事建立合作关系。科学成果也将在PI的网站上向公众展示。项目材料将被纳入华盛顿大学对当地学校、博物馆和社区团体的持续推广工作中。PI和co -PI将继续通过西雅图科学节和当地学校的其他志愿者活动参与外展活动。

Bubbles in the ocean are a key component of air-sea gas transfer at moderate to extreme wind speeds. They enhance gas transfer rate by providing a pathway in addition to the ocean surface. Due to surface tension and hydrostatic pressure exerted on bubbles, gases are able to dissolve at supersaturated conditions. The surface ocean is, therefore, supersaturated with outgassing at the ocean surface and interior dissolution through bubbles. The primary objectives of this study are to better understand processes governing the evolution of bubbles and dissolved gases under high winds and to improve parameterization for bubble-mediated gas flux. Three hypotheses, identified based on previous observational and theoretical studies, will be tested: (1) Gas dissolution through bubbles is important in determining mixed layer dissolved gas concentration under a hurricane; (2) Wind speed dependence for bubble penetration and bubble-mediated gas flux is smaller in high wind conditions; (3) Bubble-enhanced effective solubility for Dimethyl Sulfide and the kinetics of the carbonate system have substantial impacts on air-sea flux of these gases. The hypotheses will be tested using a coupled - large eddy simulation - bubble population - dissolved gas concentration model, which has been shown to faithfully reproduce the simultaneous evolution of and the interplay among oceanic surface boundary layer turbulence, bubbles of multiple sizes with multiple gas components, and the dissolved concentrations of multiple gases. The model also includes the bubble-induced enhancement in effective solubility for polar gas DMS and chemical reactions for the carbonate system. The model will be forced by realistic wind and wave conditions under hurricane Frances (2004), where high quality oceanic measurements of turbulence, dissolved oxygen and Nitrogen will be used to gauge the model realism, as well as steady winds.Intellectual Merit :Subsurface bubbles, especially in high wind conditions, are hitherto insufficiently understood, and the contributions of bubbles to the total air-sea gas flux are poorly constrained and have not yet been included in any existing climate simulations or biogeochemical process estimates. The synthesis of simulations and data will provide accurate description of processes governing bubbles and dissolved gases at high spatial and temporal resolutions. Results of this study will provide fundamental understanding of and mechanistically based parameterization for bubble distribution and bubble-mediated gas transfer. They will also be applicable to the air-sea transfer of other reactive and non-reactive gases.Broader Impacts :The research in bubbles and air-sea gas transfer in high wind conditions contributes broadly to the understanding of the earth system in terms of both the physical coupling of the ocean and atmosphere and the global biogeochemical cycling. Better parameterization of bubble-mediated gas flux for large scale and climate models will result in significant improvements in the modeling and budget estimate of climatically and environmentally important soluble gases including carbon dioxide, oxygen and Dimethyl Sulfide. This study will improve our capability to predict future environmental and climatic changes, and will provide better scientific basis for decision makers in politics and industry on a range of issues such as climate and energy. It, therefore, has important economic and societal implications. Although this study focuses on the impact of bubbles on air-sea gas transfer, better description of subsurface bubble fields also leads to better characterization of sound and light propagation at the surface ocean and benefits the ocean engineering community. The project will support a new investigator. Besides publishing in refereed journals, the PI will actively participate in conferences and workshops organized by established scientific groups and societies and will develop collaboration with other colleagues in the air-sea gas exchange community. Scientific results will also be presented to the general public on the PI's website. Project materials will be incorporated into the University of Washington's continual outreach effort to local schools, museums and community groups. The PI and Co-PIs will continue to be involved in outreach activities through the Seattle science festival and other volunteer activities at local schools.