CAREER: Mechanistic Modeling of Turbulent Bubbly Flows in the Ocean Surface Boundary Layer

海洋气泡在上层海洋动力学和海气交换中起着重要作用。该项目将研究它们在海洋表面附近的分布及其与湍流的相互作用，并改进它们对海洋和大气之间气体交换的影响在数值模式中的表示。随机分布的破碎波和小尺度海流是上层海洋中普遍存在的两个过程。它们在气泡动力学和气泡介导的气-海气体转移方面的作用从未被研究过，这可能是因为在这两个动力过程中观测和模拟气泡的挑战。利用先进的计算机模型模拟气泡和溶解气体这两个基于第一性原理的动力学过程的共同演化，这项研究将促进我们对上层海洋中气泡动力学及其与上层海洋动力学耦合的基本理解。它还将改进计算机模型中气泡介导的气体通量的表示。这项研究从上层海洋动力学和海洋生物地球化学循环两个方面加深了我们对地球系统的理解。它将减少氧气和二氧化碳等对气候和环境具有重要意义的可溶气体的建模和预算估计中的不确定性。它还将提高我们使用溶解气体，如氧气、氮气和氩的能力，这些气体的溶解浓度受气泡的影响，作为生物地球化学过程的示踪剂。预期结果还可用于理解和预测浮油和海洋塑料等海洋污染物。因此，这项研究将提高我们预测海洋环境和气候变化的能力，并将为政界和工业界的决策者在气候、环境、渔业、能源和海洋污染缓解等一系列问题上提供更好的科学依据。职业项目的教育部分包括为K-12教师开发一个为期两天的迷你讲习班，并为海洋建模实践活动创建一个互动网页，该网页将用于国际和平协会一直在教授的一个夏令营和一个非STEM学生的普通教育班。教育活动的目的是吸引当地的中学生进入海洋学领域，提高学生和公众对海洋重要性的认识，并进一步丰富路易斯安那州立大学的物理海洋学课程。本项目的主要研究目标是更好地了解海洋表面边界层中气泡的分布以及气泡与海洋湍流之间的耦合，并更准确地将气泡介导的气-海气体通量参数化。根据以前的研究和初步结果确定的两个假设将得到检验：(1)随机破碎波通过改变海洋边界层湍流并在下行流中产生气泡，影响气泡轨迹和气泡中介气体通量；(2)亚中尺度流通过与海洋边界层湍流的相互作用改变气泡轨迹和气泡中介气体通量。这些假设将使用最先进的大涡模拟建模框架进行测试。耦合建模框架由模拟随机分布破碎波冲击的海洋表面边界层湍流的大涡模拟(LES)模型、跟踪气泡和气泡特性的拉格朗日粒子模型以及溶解气体的欧拉浓度模型组成。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Oceanic bubbles play important roles in upper ocean dynamics and in air-sea gas exchange. This project will study their distribution near the ocean surface and their interaction with turbulence, and improve the representation in numerical models of their impact on the exchange of gases between the ocean and atmosphere. Randomly-distributed breaking waves and small- scale currents are two ubiquitous processes in the upper ocean. Their roles on bubble dynamics and bubble-mediated air-sea gas transfer have never been studied due likely to the challenges in observing and modeling of gas bubbles in those two dynamical processes. Utilizing state-of-the-art computer models that simulate the co-evolution of the two dynamical processes, gas bubbles, and dissolved gases based on first principles, this study will advance our fundamental understanding of bubble dynamics in the upper ocean and its coupling with upper ocean dynamics. It will also improve representation of bubble-mediated gas fluxes in computer models. This research improves our understanding of the earth system in terms of both upper ocean dynamics and ocean biogeochemical cycling. It will reduce uncertainties in the modeling and budget estimate of climatically and environmentally important soluble gases such as oxygen and carbon dioxide. It will also improve our ability to use dissolved gases such as oxygen, nitrogen and argon, whose dissolved concentrations are affected by bubbles, as tracers for biogeochemical processes. The anticipated results can also be applied to the understanding and prediction of buoyant marine pollutants including spilled oil and marine plastics. Therefore, the study will improve our capability to predict marine environment and climatic changes, and will provide better scientific basis for decision makers in politics and industry on a range of issues including climate, environment, fisheries, energy and marine pollution mitigation. The educational component of the CAREER project includes developing a two-day mini-workshop for K-12 teachers, and creating an interactive webpage for hand-on ocean modelling activities that will be used in a summer camp and a general education class for non-STEM students that the PI has been teaching. The purposes of the educational activities are to attract local middle and high school students to the field of oceanography, to raise the awareness of the importance of the ocean among students and the general public, and to further enrich the curriculum for physical oceanography at LSU.The primary research objectives of this project are to better understand the distribution of gas bubbles and the coupling between bubbles and oceanic turbulence in the ocean surface boundary layer, and to more accurately parameterize bubble-mediated air-sea gas flux. Two hypotheses, identified based on previous studies and preliminary results, will be tested: (1) Stochastic breaking waves affect bubble trajectories and bubble-mediated gas flux through altering ocean boundary layer turbulence and generating bubbles at downwelling currents; and (2) Submesoscale currents alter bubble trajectories and bubble-mediated gas flux via interaction with ocean boundary layer turbulence. These hypotheses will be tested using a state-of-the-art large eddy simulation modeling framework. The coupled modeling framework consists of a Large Eddy Simulation (LES) model that simulates the ocean surface boundary layer turbulence with the impact of stochastically distributed breaking waves, a Lagrangian particle model that tracks bubbles and bubble properties, and an Eulerian concentration model for dissolved gases.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.