Oceanic Geostrophic Turbulence Inferred From Vertical Structure Observations

从垂直结构观测推断的海洋地转湍流

• 批准号: 1736217
• 负责人: Charles Eriksen
• 金额: $ 133.78万
• 依托单位: University of Washington
• 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: 2017-09-15 至 2021-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1736217&HistoricalAwards=false
• 关键词: Oceanic; Geostrophic; Turbulence; Inferred; Vertical

Appreciation that the ocean is full of eddies on a vast array of scales began with the discovery of what are commonly referred to as mesoscale eddies: those with horizontal scales of order tens to about 100 km. These eddies are geostrophic (a state where the pressure gradient force from density gradients is in balance with the Coriolis effect from the rotation of the earth) in contrast to meteorological eddies like tornadoes which are significantly ageostrophic. Because they are the most energetic features of oceanic motion, understanding how these geostrophic eddies work is key to understanding and predicting circulation, the distribution of properties, and biomass in the ocean. Testing theories of geostrophic turbulence will stimulate new work to better understand oceanic states in the past and to predict their future. Laws for the dependence of energy wavenumber spectra implied by geostrophic turbulence were proposed on theoretical grounds half a century ago. These distinguished between an inverse cascade transferring energy to larger scale and a forward cascade transferring enstrophy (the energy of rotating motions) to shorter scale. While the existence of an enstrophy cascade has been identified in spectra of trophospheric wind observations, evidence supporting such a cascade in the ocean is scant and contradictory. Recent observations of the depth structure of current and vertical displacement at the Bermuda Atlantic Time Series (BATS) site seem to confirm the scaling predictions for both the inverse energy and forward enstrophy cascade portions of the wavenumber spectrum. These preliminary observations will be extended and generalized by sampling four new sites with distinct eddy energy and latitude regimes. This project will train a graduate student in the use of the new glider technology and join the cadre of young scientists being trained to use autonomous platforms for oceanographic research.The initial observations at the Bermuda Atlantic Time Series (BATS) site show potential energy exceeds kinetic energy by more than an order of magnitude in the steeper portion of the spectra, implying vortex stretching dominates relative vorticity in potential vorticity fluctuations in the enstrophy cascade. Temporal variations on scales of several weeks suggest that the transition wavenumber between the two slope dependences varies as the inverse cube root of vertical wavenumber which nearly preserves enstrophy regardless of eddy energy. The goal of this project is to test if: 1) energy and enstrophy transfer portions of the wavenumber spectrum of geostrophic turbulence are a general feature of ocean eddies; 2) potential energy consistently exceeds kinetic energy in the oceanic enstrophy cascade wavenumber range; and 3) enstrophy for geostrophic eddies is self-limited to modest Rossby number. To accomplish these goals, Deepglider repeat survey missions in distinctly different eddy energy and latitude regimes in both the highly energetic Northwest Atlantic and the eddy desert of the Gulf of Alaska in the Northeast Pacific will be conducted. Missions will rely on chartered small boats or, in one case, on ancillary use of a large vessel. The approach at each site is to survey from surface to bottom a roughly 100 km by 100 km region of ocean along a common track every three weeks or so for a year. By comparing estimates from BATS and four new sites, at least a preliminary climatology of the geostrophic eddy inverse energy and forward enstrophy cascades will be created. These calculations will provide rich targets for new theories and numerical models of the ocean.

人们认识到海洋中充满了各种尺度的涡旋，这是从发现通常所说的中尺度涡旋开始的：这些涡旋的水平尺度从几十公里到大约100公里。这些涡旋是地转的（密度梯度产生的压力梯度力与地球自转产生的科里奥利效应平衡的状态），与气象涡旋（如显著非地转的龙卷风）形成对比。因为它们是海洋运动中最具能量的特征，所以了解这些地转涡旋是如何工作的，是了解和预测海洋环流、性质分布和生物量的关键。测试地转湍流理论将激发新的工作，以更好地了解过去的海洋状态，并预测其未来。半个世纪以前，人们就从理论上提出了地转湍流所隐含的能量波数谱依赖性规律。这两种情况是将能量传递到大尺度的逆叶栅和将涡度拟能（旋转运动的能量）传递到小尺度的正叶栅。虽然涡度拟能级联的存在已被确定在热带风观测谱，证据支持这样的级联在海洋中是稀缺的和矛盾的。最近在百慕大大西洋时间序列（BATS）网站的深度结构的电流和垂直位移的观测似乎证实了缩放预测的逆能量和向前涡度拟能级联部分的波数谱。这些初步的意见将扩大和推广的采样四个新的网站与不同的涡能量和纬度制度。该项目将培训一名研究生使用新的滑翔机技术，并加入正在接受培训的青年科学家骨干队伍，使用自主平台进行海洋学研究。百慕大大西洋时间序列（BATS）站点的初步观测表明，在光谱的较陡部分，势能超过动能一个数量级以上，这意味着涡拉伸在涡度拟能叶栅的位涡波动中占主导地位。几个星期的尺度上的时间变化表明，两个斜率依赖性之间的过渡波数变化的垂直波数的倒数的立方根，几乎保留涡度拟能，无论能量。该项目的目标是测试：1）地转湍流波数谱的能量和涡度拟能传输部分是否是海洋涡旋的一般特征; 2）在海洋涡度拟能级联波数范围内，势能始终超过动能;和3）地转涡旋的涡度拟能自限为适度的罗斯比数。为了实现这些目标，Deepglider将在东北太平洋的高能西北大西洋和阿拉斯加湾的涡流沙漠中进行明显不同的涡流能量和纬度区域的重复调查任务。各特派团将依靠租用的小船，或在一个情况下辅助使用一艘大船。每个地点的方法是沿着一条共同的轨迹，每三周左右对大约100公里乘100公里的海洋区域进行从表面到底部的调查，为期一年。通过比较BATS和四个新站点的估计，至少可以创建一个初步的地转涡旋逆能量和正向涡度拟能级联的气候学。这些计算将为新的海洋理论和数值模式提供丰富的目标。

项目成果

Eddy Vertical Structure and Variability: Deepglider Observations in the North Atlantic

涡流垂直结构和变化：北大西洋的深滑翔机观测

• DOI: 10.1175/jpo-d-21-0068.1
• 发表时间: 2022
• 期刊: Journal of Physical Oceanography
• 影响因子: 3.5
• 作者: Steinberg, Jacob M.;Eriksen, Charles C.
• 通讯作者: Eriksen, Charles C.

Assessing Seaglider® Model-based Position Accuracy on an Acoustic Tracking Range

评估声学跟踪范围内基于 Seaglider® 模型的位置精度

• DOI: 10.1175/jtech-d-20-0091.1
• 发表时间: 2021
• 期刊: Journal of Atmospheric and Oceanic Technology
• 影响因子: 2.2
• 作者: Bennett, James S.;Stahr, Frederick R.;Eriksen, Charles C.;Renken, Martin C.;Snyder, Wendy E.;Van Uffelen, Lora J.
• 通讯作者: Van Uffelen, Lora J.

Glider Sampling Simulations in High-Resolution Ocean Models

高分辨率海洋模型中的滑翔机采样模拟

• DOI: 10.1175/jtech-d-19-0200.1
• 发表时间: 2020
• 期刊: Journal of Atmospheric and Oceanic Technology
• 影响因子: 2.2
• 作者: Steinberg, Jacob M.;Eriksen, Charles C.
• 通讯作者: Eriksen, Charles C.