Generation of sea sprays and their impact on near surface turbulence and air-sea momentum flux

该奖项是根据2009年《美国复苏和再投资法》(公法111-5)资助的。智力上的优点：海气动量和热通量的准确预测/参数很重要，因为它们为大气、海洋和海洋大气耦合模式提供了边界条件。特别是，热带气旋模式预报对大风条件下的海气通量参数化非常敏感。最近的现场观测表明，在很高的风速下，动量通量(阻力)系数往往比现有的总体参数低得多。这种阻力减少的一个可能原因是大风中海面破碎波产生的大量海浪的影响。研究人员假设：(1)海洋喷雾在改变近地表大气湍流以及高风速下的海气动量和热通量方面发挥了重要作用；(2)对海雾生成的准确预测必须考虑到各种尺度上单个破碎波事件的破碎波和水雾生成过程的统计数据；(3)准确模拟海雾-湍流相互作用需要一种新的数值方法，该方法明确地解决单独的水雾或液团与由破碎波改变的湍流气流的相互作用。为了验证这些假设，研究人员将继续进行一项研究计划，其长期目标是开发新的混合数值模拟方法-结合目前可用的最佳工具之一的模式组件-研究海雾的生成过程以及喷雾和近地表湍流之间的相互作用，并预测大风条件下海雾对海气动量和热通量的影响。作为实现这些长期目标的第一步，重点将放在开发一种模拟方法的两个主要具体目标上：(1)使用完全非线性势波求解器和格子-Boltzmann方法相结合的混合方法来模拟单个破碎波事件的水雾生成过程；(2)使用格子-Boltzmann方法来模拟两相流体动力学中分解的喷雾液滴(或分解的小气团)与湍流剪切流之间的相互作用。利用这种方法，我们将研究海面喷雾对海气动量通量的潜在影响。这项工作将由URI的原哲博士、斯蒂芬·格里利博士和德国布伦斯韦格工业大学的曼弗雷德·克拉夫奇克共同完成。此外，将与特拉华大学的Fabrice Veron博士合作，根据实验室观察验证喷雾生成模型。更广泛的影响：该项目的更广泛影响在五个方面显而易见。首先，拟议的工作为了解海洋喷雾如何影响海-气通量，以及这种修正的通量进而如何影响大风时的大气和海洋预报提供了基础。海面通量的估算是海洋和大气模拟中最关键的问题之一，包括热带气旋和风暴潮模拟。事实上，通量参数的主要不确定因素之一是海面喷雾的影响。他的研究面向社会？S需要减轻和预防极端风浪可能造成的自然灾害。因此，这项研究将产生更准确的风暴和飓风预报，从而导致更长的预警时间，从而增加准备时间，以减轻这种危险，并有望减少死亡和财产损失。发展一种新的结合不同数值方法的混合方法，不仅有利于海洋/大气模拟领域，也将有利于广泛的流体力学应用领域。第四，该项目将支持两名研究生，因此将有助于教育和培训新一代科学家/工程师，他们完全精通最先进的环境建模。最后，这项拟议的工作促进了研究和教育方面的国际合作，因为它涉及美国和德国科学家的密切合作。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Intellectual Merit: Accurate predictions/parameterizations of air-sea momentum and heat fluxes are important because they provide boundary conditions for atmospheric, oceanic and coupled ocean atmosphere models. In particular, tropical cyclone model prediction is very sensitive to air-sea flux parameterizations under high wind conditions. Recent field observations suggest that the momentum flux (drag) coefficient tends to be much lower than the existing bulk parameterizations at very high wind speeds. One possible reason for this drag reduction is the effect of sea sprays generated in great amount by surface breaking waves in high winds. The investigators hypothesize that: (1) sea sprays play an important role in modifying the near surface atmospheric turbulence and air-sea fluxes of momentum and heat at high wind speeds; (2) accurate predictions of sea spray generation must account for statistics of breaking waves and spray generation processes from individual breaking wave events over a range of scales; and (3) accurate modeling of sea spray-turbulence interactions requires a new numerical methodology that explicitly resolves individual spray droplets or fluid parcels interacting with the turbulent air flow that is modified by breaking waves. To test these hypotheses the investigators will pursue a research program, whose long term objectives are to develop new hybrid numerical simulation methodologies - combining model components that are among the best currently available tools - to study sea spray generation processes and interactions between sprays and near surface turbulence, and to predict sea spray effects on air-sea momentum and heat fluxes in high wind conditions. As a first step towards meeting these long term objectives, the focus will be on two main specific objectives in developing a methodology to simulate: (1) spray generation processes from one single breaking wave event, using a hybrid approach combining a fully nonlinear potential wave solver and a Lattice-Boltzmann method for two-phase fluid dynamics; and (2) interactions between resolved spray droplets (or resolved small air parcels) and a turbulent shear flow, using the Lattice-Boltzmann method for two-phase fluid dynamics. Using this methodology we will investigate the potential effects of sea sprays on the air-sea momentum flux. The work will be performed as a collaboration between Drs. Tetsu Hara, Stephan Grilli, of URI, and Manfred Krafczyk, Technical University of Braunschweig, Germany. In addition the spray generation model will be validated against laboratory observations, in collaboration with Dr. Fabrice Veron, University of Delaware.Broader impacts: The broader impacts of the project are evident in five areas. First, the proposed work provides a basis for understanding how sea sprays affect air-sea fluxes and how such modified fluxes consequently impact atmospheric and ocean predictions at high winds. Estimation of fluxes over the sea surface is one of the most crucial issues in ocean and atmospheric modeling, including tropical cyclone and storm surge modeling. In fact, one of the main uncertainties regarding the flux parameterizations is the effect of sea sprays. his research addresses society?s need to mitigate and prevent possible natural hazards caused by extreme winds and waves. The more accurate storm and hurricane forecasts that will result from this research will thus lead to a longer advance warning and hence increased preparation time, for mitigating such hazard and hopefully diminishing fatalities and property damage. The development of a new hybrid approach combining different numerical methods will benefit not only the field of oceanographic/atmospheric modeling but also a wide range of applied fluid dynamics community. Fourth, the project will support two graduate students, and hence will contribute to the education and training of a new generation of scientists/engineers, fully fluent with state-of-the-art environmental modeling. Finally, the proposed work promotes international cooperation in research and education, since it involves a close collaboration of US and German scientists.