Wave-topography interaction and impact on oceanic kinetic energy distribution

波浪地形相互作用及其对海洋动能分布的影响

• 批准号: 1737389
• 负责人: Cimarron Wortham
• 金额: $ 19.05万
• 依托单位: NorthWest Research Associates, Incorporated
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-09-01 至 2021-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1737389&HistoricalAwards=false
• 关键词: Wave; topography; interaction; impact; oceanic

The impact of variable topography on Rossby waves and mesoscale eddies is a basic question in geophysical fluid dynamics, and topography can alter the vertical structure and phase speed of Rossby waves and nonlinear eddies. The vertical structure of eddies in turn impacts the vertical structure of ocean eddy kinetic energy (EKE) and hence horizontal stirring. Therefore, understanding the impact of topography on the propagation (phase speed) and vertical structure of geostrophic motions is of global significance. Specifically, eddy phase speed has been shown to modulate eddy fluxes of heat and salt, so understanding the phase speed and structure of eddies is directly relevant to the development of improved eddy parameterizations for coarse-resolution ocean models. Also, satellite altimetry provides accurate, global measurements of mesoscale EKE at the ocean surface, but no way to extrapolate to depth. An improved understanding of the vertical structure of oceanic eddies is necessary to estimate sub-surface EKE from readily available surface observations. The research will investigate the impact of variable topography with scales of 10-100km on geostrophically balanced motions, e.g. Rossby waves and nonlinear mesoscale eddies. The code for computing the Rossby wave modes with topography will be made publicly available, along with the algorithm for projecting surface EKE estimates to depth. This project will support an early-career researcher in his first independent study. The researcher is a Pacific Science Center Science Communication Fellow, and regularly participates in "Meet a Scientist" outreach programs. The proposed work will complement this ongoing outreach efforts.Bottom topography with wavelengths on the order of 10-100km is nearly ubiquitous in the ocean, appearing on the flanks of mid-ocean ridges and near seamounts. Previous idealized theoretical and modeling studies have shown that topography on these scales can impact the vertical structure and propagation speed of linear Rossby waves and eddies. The impact of topography in more realistic cases, including nonlinear dynamics in a stratified ocean with realistic topography, remains to be examined. Further, the dependence on important parameters, including topographic amplitude, topographic wavelength, bottom friction, and stratification, has not been fully explored. Finally, the topographically altered vertical structure of nonlinear eddies may have an important impact on the turbulent energy cascade and barotropization. This is an analytical and modeling study to systematically explore these effects. Specific goals are to (1) determine whether previous linear solutions with one-dimensional topography carry over to the nonlinear regime with two-dimensional topography in a quasigeostrophic (QG) numerical model, (2) examine the vertical structure of eddies in historical current-meter records and an ocean general circulation model (OGCM) to determine the extent to which topography has an observable impact on mesoscale eddy vertical structure, and (3) study the impact of topography on the turbulent energy cascade and energy dissipation, through its effect on the vertical structure of currents.

地形变化对Rossby波和中尺度涡旋的影响是地球物理流体动力学中的一个基本问题，地形可以改变Rossby波和非线性涡旋的垂直结构和相速度。涡旋的垂直结构反过来影响海洋涡旋动能的垂直结构，从而影响水平搅拌。因此，了解地形对地转运动的传播（相速度）和垂直结构的影响具有全球意义。具体而言，涡流相速度已被证明调制涡流通量的热量和盐，因此了解相速度和结构的涡流是直接相关的发展改进的涡流参数化的粗分辨率海洋模型。此外，卫星测高提供了精确的，全球测量的中尺度EKE在海洋表面，但没有办法外推到深度。海洋涡旋的垂直结构的一个更好的理解是必要的，以估计次表面EKE从现成的表面观测。这项研究将调查尺度为10- 100公里的可变地形对地转平衡运动的影响，例如Rossby波和非线性中尺度涡旋。用于计算具有地形的Rossby波模式的代码将公开提供，沿着用于将表面EKE估计投影到深度的算法。该项目将支持一位早期职业研究人员进行他的第一次独立研究。该研究员是太平洋科学中心的科学传播研究员，并定期参加“与科学家见面”外展计划。拟议的工作将补充这一正在进行的推广工作，波长在10- 100公里左右的海底地形在海洋中几乎无处不在，出现在大洋中脊的侧面和海山附近。先前的理想化理论和模拟研究表明，这些尺度上的地形可以影响线性Rossby波和涡旋的垂直结构和传播速度。在更现实的情况下，地形的影响，包括在一个分层的海洋与现实的地形的非线性动力学，仍有待研究。此外，对重要参数的依赖性，包括地形振幅，地形波长，底摩擦，和分层，还没有得到充分的探讨。最后，地形改变的非线性涡旋的垂直结构可能有重要的影响湍流能量级联和正压。这是一个分析和建模研究，系统地探讨这些影响。具体目标是：（1）确定在准地转（QG）数值模式中，一维地形的线性解是否延续到二维地形的非线性解;（2）检查历史流速仪记录和海洋环流模式（OGCM）中的涡旋垂直结构，以确定地形对中尺度涡旋垂直结构的可观测影响程度;（3）通过地形对水流垂向结构的影响，研究地形对湍流能量级联和能量耗散的影响。