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

海洋中的气泡是中等至极端风速下海气传输的关键组成部分。它们通过提供除了海洋表面之外的路径来提高气体传输速率。由于表面张力和静水压力施加在气泡上，气体能够在过饱和条件下溶解。因此，海洋表面由于海洋表面的释气和内部通过气泡的溶解而过饱和。本研究的主要目的是更好地了解过程中的气泡和溶解气体的演变大风和改善参数化气泡介导的气体通量。根据以往的观测和理论研究，将检验三个假设：（1）通过气泡的气体溶解在确定飓风下混合层溶解气体浓度方面很重要;（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）气泡增强的有效溶解度和碳酸盐体系的动力学对二甲基硫的海气通量有重要影响。将使用耦合-大涡模拟-气泡群-溶解气体浓度模型对假设进行测试，该模型已被证明能够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的同时演变和相互作用。该模型还包括极性气体DMS和碳酸盐体系的化学反应的有效溶解度的气泡诱导的增强。该模型将受飓风弗朗西斯（2004年）下的真实风和波浪条件的影响，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风。地下气泡，特别是在大风条件下，迄今为止还没有得到充分的了解，以及气泡对空气总量的贡献-海洋气体通量受到的限制很小，尚未纳入任何现有的气候模拟或地球化学过程估计。模拟和数据的合成将提供高空间和时间分辨率的气泡和溶解气体的过程的准确描述。这项研究的结果将提供基本的理解和机械为基础的参数化气泡分布和气泡介导的气体传输。更广泛的影响：在强风条件下对气泡和海气气体传输的研究有助于从海洋和大气的物理耦合以及全球地球化学循环的角度了解地球系统。更好的参数化气泡介导的气体通量的大规模和气候模式将导致显着改善气候和环境重要的可溶性气体，包括二氧化碳，氧气和二甲基硫的建模和预算估计。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。虽然这项研究的重点是气泡对空气-海洋气体传输的影响，但更好地描述地下气泡场也可以更好地表征海洋表面的声和光传播，并使海洋工程界受益。该项目将支持一名新的调查员。除了在权威期刊上发表论文外，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，并将与海气交换界的其他同事开展合作。科学结果也将在PI的网站上向公众展示。项目材料将纳入华盛顿大学对当地学校、博物馆和社区团体的持续宣传工作。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.