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

在中等到极端风速下，海洋中的气泡是海-气转移的关键组成部分。它们除了在海洋表面外，还提供了一条途径，从而提高了气体的传输速度。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，表层海洋是过饱和的，海洋表面放出气体，内部通过气泡溶解。这项研究的主要目的是更好地了解大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。根据以前的观测和理论研究确定的三个假设将得到检验：(1)气体通过气泡的溶解对于确定飓风下混合层的溶解气体浓度是重要的；(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很大影响。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检验，该模型已被证明真实地再现了海洋表面边界层湍流、具有多种气体成分的多种尺寸的气泡以及多种气体的溶解浓度之间的同时演变和相互作用。该模型还考虑了气泡诱导的极性气体DMS有效溶解度的增加和碳酸盐体系的化学反应。模型将受到飓风France(2004)下的实际风和波浪条件的影响，其中将使用高质量的湍流、溶解氧和氮的海洋测量来衡量模型的现实性，以及稳定的风。智力上的优点：到目前为止，对次表层气泡，特别是在大风条件下，了解得还不够充分，而且气泡对海-气总通量的影响限制很差，还没有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管理气泡和溶解气体的过程的准确描述。这一研究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法。它们还将适用于其他反应性和非反应性气体的海-气转移。辐射影响：对大风条件下气泡和海-气转移的研究有助于从海洋和大气的物理耦合和全球生物地球化学循环两方面广泛理解地球系统。对于大尺度和气候模型，气泡介导的气体通量的更好的参数化将导致对包括二氧化碳、氧气和二甲基硫化物在内的气候和环境重要的可溶气体的建模和预算估计的显著改进。这项研究将提高我们预测未来环境和气候变化的能力，并将为政界和工业界在气候和能源等一系列问题上的决策者提供更好的科学依据。因此，它具有重要的经济和社会影响。虽然本研究的重点是气泡对海-气传输的影响，但更好地描述次表层气泡场也有助于更好地描述表层海洋中的声和光传播，并有利于海洋工程界。该项目将支持一名新的调查员。除了在被引用的期刊上发表文章外，PI还将积极参加由现有科学团体和学会组织的会议和研讨会，并将与海空气体交换界的其他同事发展合作。科学成果也将在国际和平研究所的网站上向公众公布。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外展努力。PI和共同PIS将继续通过西雅图科学节和当地学校的其他志愿活动参与外联活动。

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.