Collaborative Research: Langmuir Turbulence Under Tropical Cyclones

合作研究：热带气旋下的朗缪尔湍流

• 批准号: 1129985
• 负责人: Tetsu Hara
• 金额: $ 37.62万
• 依托单位: University of Rhode Island
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-09-01 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1129985&HistoricalAwards=false
• 关键词: Collaborative; Research; Langmuir; Turbulence; Under

Turbulent mixing in the ocean surface layer under tropical cyclones effectively couples the ocean and atmosphere through air-sea fluxes of heat and momentum. Air-sea heat fluxes sustain Tropical Cyclones and strongly depend on near surface temperature, which is determined by mixing with cooler deeper water. Understanding the turbulent processes involved in near-surface layer mixing remains one of the great challenges in modeling the coupled ocean-Tropical Cyclone system. Upper ocean turbulence is driven by the surface wind stress, resulting in sheared subsurface currents. Furthermore, surface gravity waves influence upper ocean turbulence through wave-current interactions that lead to wind-aligned vortices, called Langmuir circulation or Langmuir turbulence. Wave effects on ocean turbulence are particularly complex under Tropical Cyclones, since wind, wave, and current fields are inhomogeneous and may be misaligned. In addition, the surface wave height spectrum can comprise multiple peaks at different wave frequencies and directions. The proposed work is aimed at understanding Langmuir circulation under realistic Tropical Cyclone conditions and at assessing the role of Langmuir circulation on the coupled ocean-wave-atmosphere Tropical Cyclone dynamics. This project addresses the following hypotheses: Langmuir circulation characteristics under Tropical Cyclones critically depend on detailed wind, wave, and current conditions. Specifically, regions under Tropical Cyclones exist where upper ocean mixing is greatly influenced by Langmuir circulation. The use of an ocean mixing scheme with explicit Langmuir circulation effects will lead to significantly modified mixing and sea surface temperature cooling in Langmuir circulation regions. Including explicitly the Langmuir circulation effect will have a significant effect on the three-dimensional Tropical Cyclone dynamics and prediction.These hypotheses will be tested by applying synergistically a coupled atmosphere-wave-ocean model (AWO) and a turbulence resolving large eddy simulation model (LES) that captures Langmuir circulation. Initially, the AWO will provide critical output (wind, waves, and currents) to drive the LES model. LES results, in turn, will aid in characterizing Langmuir circulation under tropical cyclones and in critically assessing the ocean mixing parameterization. Finally, a turbulent mixing scheme with explicit Langmuir circulation and turbulence effects will be implemented in the ocean model component of the AWO model and a sensitivity study by simulating idealized and real case tropical cyclones will be performed. The model results will then be validated against available field observations in collaboration with scientists at the University of Washington. Intellectual Merit: This project investigates ocean and atmosphere dynamics under Tropical Cyclones, which are coupled through turbulent upper ocean mixing. The investigators will examine an insufficiently understood turbulent process, Langmuir circulation, that is not explicitly represented in most ocean models, despite the fact that Langmuir circulation and turbulence may be a principal mixing component. The combination of regional and process-based models is anticipated to significantly advance our understanding of Langmuir circulation under Tropical Cyclones. Broader Impact: While pursuing some fundamental scientific questions related to air-sea interactions, turbulent mixing, and Tropical Cyclone dynamics, the research will aid in addressing an important societal challenge. Tropical Cyclones critically disrupt infrastructure, cause severe flooding, and displace people in coastal regions. The investigator will advance the scientific basis of Tropical Cyclones models and improve their prediction skill, which will ultimately lead to increased reliability of hurricane forecasts and thus confidence in the official hurricane warnings. The resources from the proposed grant will train two doctoral graduate researchers. The outreach effort will educate the public about basic science with its societal impacts through special events (e.g., at the Open House at the University of Delaware). Science material developed in the course of this project will contribute to the University of Rhode Island comprehensive educational website Hurricanes: Science and Society (www.hurricanescience.org). The website provides information on the science of hurricanes, how hurricanes impact society, and how people and communities can prepare for and mitigate the impacts of hurricanes.

热带气旋作用下海洋表层的湍流混合通过海气热量和动量通量有效地耦合了海洋和大气。海气热通量支持热带气旋，并强烈依赖于近地表温度，这是由与较冷的深层水混合而决定的。理解近地面层混合所涉及的湍流过程仍然是模拟海洋-热带气旋耦合系统的巨大挑战之一。上层海洋湍流是由表面风应力驱动的，导致了次表层海流的切变。此外，表面重力波通过波-流相互作用影响上层海洋湍流，导致风向涡旋，称为朗缪尔环流或朗缪尔湍流。在热带气旋下，海浪对海洋湍流的影响特别复杂，因为风、浪和流场是不均匀的，可能会错位。此外，面波高度谱可以包括位于不同波频率和方向的多个峰。这项拟议的工作旨在了解现实热带气旋条件下的朗缪尔环流，并评估朗缪尔环流在海-波-大气耦合热带气旋动力学中的作用。本项目提出了以下假设：热带气旋下的朗缪尔环流特征主要取决于具体的风、浪和海流条件。具体地说，热带气旋下存在上层海洋混合受朗缪尔环流影响较大的区域。具有明显朗缪尔环流效应的海洋混合方案的使用将导致朗缪尔环流区的混合和海表面温度冷却的显着修正。明确包括朗缪尔环流效应将对三维热带气旋动力学和预报产生重大影响。这些假设将通过应用大气-波浪-海洋耦合模式(AWO)和捕捉朗缪尔环流的湍流分辨大涡模拟模式(LES)来检验。最初，AWO将提供关键输出(风、浪和流)来驱动LES模型。LES结果反过来将有助于描述热带气旋下的朗缪尔环流特征，并有助于对海洋混合参数化进行批判性评估。最后，将在AWO模式的海洋模式部分实施具有明显的朗缪尔环流和湍流效应的湍流混合方案，并将通过模拟理想化和真实的热带气旋进行敏感性研究。然后，将与华盛顿大学的科学家合作，根据可用的现场观测来验证模型结果。学术价值：这个项目研究热带气旋下的海洋和大气动力学，热带气旋通过湍流的上层海洋混合而耦合。研究人员将研究一种尚未被充分理解的湍流过程--朗缪尔环流，尽管朗缪尔环流和湍流可能是主要的混合成分，但大多数海洋模型中没有明确表示这一过程。区域模式和过程模式的结合有望极大地促进我们对热带气旋下朗缪尔环流的理解。更广泛的影响：在探索与海-气相互作用、湍流混合和热带气旋动力学相关的一些基本科学问题的同时，这项研究将有助于解决一个重要的社会挑战。热带气旋严重扰乱基础设施，造成严重洪灾，并使沿海地区的人们流离失所。调查员将推进热带气旋模型的科学基础，并改进其预测技能，这最终将导致飓风预测的可靠性增加，从而提高对官方飓风警报的信心。拟议拨款的资源将培训两名博士研究生研究人员。外展工作将通过特别活动(例如，在特拉华大学的开放日)教育公众有关基础科学及其社会影响的知识。在该项目过程中开发的科学材料将为罗德岛大学综合教育网站飓风：科学和社会(www.hurricanescience.org)作出贡献。该网站提供有关飓风科学、飓风如何影响社会以及人们和社区如何为飓风的影响做好准备和减轻影响的信息。