Research in Linear and Nonlinear Baroclinic Waves and Ocean Circulation Theory

摘要本研究的目的是研究实验室破碎波中能量耗散与气泡产生之间的联系。破碎波的能量耗散是许多重要的上层海洋过程的关键，包括动量传递和气泡介导的海气输送。这项研究建立在早期美国国家科学基金会资助的结果上，以确定破碎波峰中的气泡产生机制。早期的研究发现了跳水破碎机内气泡形成过程的尺度依赖性：由湍流压力波动的破碎力和表面张力的稳定力（Hinze尺度）的比值决定的大于长度尺度的气泡会受到一连串破碎事件的影响。小于欣兹尺度的气泡在紊流破碎时是稳定的。本研究要解决的两个主要问题是：1)破碎波峰的湍流能量耗散如何随波能和波斜率的变化而变化；2)Hinze尺度是否如预测的那样随固有波能耗散而变化？研究计划包括测量不同波能和坡面下破碎波峰内的能量耗散，估计湍流泡破碎的Hinze尺度作为能量耗散的函数。能量耗散的估计将通过研究玻璃壁水槽中波浪能量和斜率范围的破碎波包来获得，波浪能量和斜率范围随着包的光谱组成的变化而变化。通过定量分析生物发光鞭毛藻的发光和能量守恒两种方法独立估算破峰区域内的能量耗散率。使用生物发光来量化湍流是一项最近的技术，但已被证明对短暂的两相流是有效的。利用光学技术和电导率电池，可以得到破碎过程中气泡的大小分布和空气的空隙率。气泡Hinze尺度对应于气泡尺寸分布斜率的显著变化，这可以从光学测量中估计出来。破碎过程中损失的总能量将通过破碎上游和下游测量的波包形状变化来估计，破碎结束时相干和湍流流体运动的剩余能量将通过声学多普勒测速仪和多事件集合平均来测量。更广泛的影响。该项目将加强对大气动量向海洋输送、控制气体输送的小规模物理过程以及海洋边界层和沿海地区湍流和气泡产生的理解。所有这些过程对大气-海洋耦合动力学、全球气候模拟和沿海海洋学都有广泛的影响。实验和数据分析将包括来自加州大学圣地亚哥分校的研究生和本科生实习生以及SIO暑期研究奖学金项目的参与。这些项目资助来自全国各地的学生获得海洋学的实践经验。与加州海洋科学教育卓越中心合作，研究小组还与海洋研究所（海洋气泡！）制定了一项外展计划，以增加公众对海洋-大气相互作用的了解。

ABSTRACTOCE-0450974The objective of this research is to study the link between energy dissipation and bubble creation in laboratory breaking waves. Energy dissipation by breaking waves is key to a number of important upper-ocean processes, including momentum transfer and bubble-mediated air-sea gas transport. This study builds on the results of an earlier NSF grant to identify bubble creation mechanisms within breaking wave crests. The earlier study identified the scale dependence of bubble creation processes within plunging breakers: bubbles larger than a length scale determined by the ratio of the fragmenting forces of turbulent pressure fluctuations and the stabilizing force of surface tension (the Hinze scale) are subject to a cascade of fragmentation events. Bubbles smaller than the Hinze scale are stabilized against turbulent fragmentation. The two main questions to be addressed in this study are: 1) how does the turbulent energy dissipated in the breaking wave crest vary with variations in wave energy and wave slope and 2) does the Hinze scale vary with intrinsic wave energy dissipation as predicted? The research plan consists of measuring of energy dissipation within breaking wave crests for various wave energies and slopes, and estimating the Hinze scale for turbulent bubble fragmentation as a function of energy dissipation. Estimates of energy dissipation will be obtained by studying breaking wave packets in a glass-walled flume for a range of wave energies and slopes, varied by changing the spectral composition of the packets. The energy dissipation rate within the breaking crest region will be independently estimated with two methods: quantitative analysis of the light emission from bioluminescent dinoflagellates, and conservation of energy. Using bioluminescence to quantify turbulence is a recent technique, but has proven effective for transitory, two phase flows. The bubble size distribution and void fraction of air during breaking will be obtained using optical techniques and a conductivity cell. The bubble Hinze scale corresponds to a distinctive change in slope of the bubble size distribution, which can be estimated from the optical measurements. The total energy lost during breaking will be estimated from changes in wave packet shape measured upstream and downstream of breaking, and the residual energy in coherent and turbulent fluid motions at the end of breaking will be measured with acoustic Doppler velocimeters and ensemble averaging of multiple events. Broader Impact. The project will enhance the understanding of atmospheric momentum transport to the ocean, the small-scale physical processes controlling gas transport, and turbulence and bubble production in the marine boundary layer and coastal regions. All of these processes have a broad impact on atmosphere-ocean coupling dynamics, global climate modeling and coastal oceanography. The experiment and data analysis will include the participation of a graduate student and undergraduate interns from UCSD and the SIO summer research fellowship program. These programs sponsor students from around the country to gain hands-on experience in oceanography. Working with the California Center for Ocean Science Education Excellence, the research team is also developing an outreach plan with the Ocean Institute (Sea Bubbles!) so as to increase public understanding of ocean-atmospheric interactions.