Collaborative Research: Experiment on Internal Tide Scattering

合作研究：内潮汐散射实验

• 批准号: 0825266
• 负责人: Glenn Carter
• 金额: $ 57.48万
• 依托单位: University of Hawaii
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-09-01 至 2014-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0825266&HistoricalAwards=false
• 关键词: Collaborative; Research; Experiment; Internal; Tide

Tides rival winds as an energy source for mixing in the deep ocean, yet the pathways of energy transfer from basin-scale tidal flows to turbulent mixing scales are not well understood. Over the past decade, many observations have shown barotropic tidal flow over steep, tall mid-ocean topography generates low-mode (large-scale) internal tides. Most of the energy lost from barotropic tides at these sites is carried away by internal tides with decay scales of O(1000 km). With few in situ observations away from internal tide generation sites, the ultimate fate of these low-mode internal tides and their energy is uncertain. This project will examine how topographic scattering of internal tides from large to small scales dissipates their energy via micro-scale mixing. Topographic scattering may also be a sink for wind-driven near-inertial internal waves. Hutchinson Seamount in the Line Islands Ridge will serve as an ideal test site, which lies in the path of energetic mode-1 internal tides emanating southward from the Hawaiian Ridge. Numerical models show the conversion of energy from a low-mode structure to a localized beam of energy with enhanced vertical shear and mixing. Altimetry provides unambiguous support for the model predictions of energy transfer from mode 1 to 2 downstream of the seamount. This project will observe the internal tide scattering process, quantify the associated mixing relative to the temporal and spatial structures of the scattered waves, verify model predictions, and improve model capabilities. Moorings will be deployed upstream (with respect to the incoming internal tides), on top, and downstream of the seamount for 150 days. A survey on R/V Revelle will provide spatial coverage at 19 stations with lowered acoustic Doppler current profiling/CTD/micro-structure to map 1) the incident and scattered wave fields near the seamount and 2) mixing via direct measurements, Thorpe scales, and fine-scale parameterizations. The mooring time series will isolate the tidal signal from background variability. A new numerical modeling study of the scattering will help refine the sampling plan and interpret the data. Internal tides impact the magnitude and inhomogeneity (in time and space- vertically and laterally) of diapycnal mixing. The meridional overturning circulation is likely not a heat engine, but is driven energetically by deep-ocean mixing. The relevance of global models, most with uniform mixing, of past or future climate is at issue if they are tuned to reproduce present observations, but do not include spatially and temporally inhomogeneous diapycnal mixing. Internal tide scattering is important where baroclinic tides are large and topography is tall and steep, such as in the Western Pacific and at mid-ocean ridges. The investogators will validate their numerical models against their experimental results for 2D and 3D topography in linear and nonlinear regimes. Graduate students and interns will gain experience with state-of-the-art instrumentation. Results will be broadly disseminated to the public by developing in cooperation with other researchers a Wikipedia entry on internal tides, their importance in mixing, and relevance to global circulation and climate. This website is often top ranked in internet searches and has the potential to reach millions of interested people in the general public as well as students. Publication of results in popular science magazines and websites will be sought via a press release from the Scripps Communications Office. Results will be disseminated in the oceanographic community by presentations at the International Union of Geophysics and Geodesy meeting in 2011 and the Ocean Sciences meeting in 2012 and by publishing in peer-reviewed journals.

潮汐作为深海混合的能源与风相媲美，但从盆地规模的潮汐流到湍流混合规模的能量转移路径尚不清楚。在过去的十年中，许多观测表明，在陡峭、高大的海洋中部地形上的正压潮汐流会产生低模式（大规模）内潮汐。这些地点的正压潮汐损失的大部分能量被衰减规模为 O(1000 km) 的内潮汐带走。由于远离内潮产生地点的现场观测很少，这些低模式内潮及其能量的最终命运是不确定的。该项目将研究内潮汐从大到小尺度的地形散射如何通过微尺度混合消散能量。地形散射也可能是风驱动的近惯性内波的汇。莱恩群岛海岭的哈钦森海山将成为理想的测试地点，该海山位于从夏威夷海脊向南发出的高能模式 1 内潮汐的路径上。数值模型显示能量从低模结构转换为具有增强的垂直剪切和混合的局部能量束。高度测量为海山下游从模式 1 到模式 2 的能量转移模型预测提供了明确的支持。该项目将观测内潮汐散射过程，量化相对于散射波时空结构的相关混合，验证模型预测并提高模型能力。系泊装置将部署在海山上游（相对于即将到来的内潮）、顶部和下游，为期 150 天。 R/V Revelle 的调查将通过降低声学多普勒电流剖面/CTD/微观结构提供 19 个站的空间覆盖，以绘制 1) 海山附近的入射波场和散射波场以及 2) 通过直接测量、索普尺度、和精细参数化。系泊时间序列将潮汐信号与背景变化隔离开来。一项新的散射数值模型研究将有助于完善采样计划并解释数据。内潮汐影响地幔混合的幅度和不均匀性（在时间和空间上，垂直和横向）。经向翻转环流很可能不是热机，而是由深海混合强力驱动的。如果全球模型（大多数具有均匀混合）过去或未来气候的相关性被调整为再现当前的观测结果，但不包括空间和时间上不均匀的二重混合，那么它们的相关性就会受到质疑。在斜压潮汐较大且地形又高又陡的地方，例如在西太平洋和洋中脊，内潮散射非常重要。研究人员将根据线性和非线性状态下 2D 和 3D 形貌的实验结果验证他们的数值模型。研究生和实习生将获得最先进仪器的经验。研究结果将通过与其他研究人员合作开发关于内潮汐、内潮汐混合的重要性以及与全球环流和气候的相关性的维基百科条目来向公众广泛传播。该网站通常在互联网搜索中名列前茅，并且有可能吸引数百万感兴趣的公众和学生。斯克里普斯通讯办公室将通过新闻稿寻求在科普杂志和网站上发表结果。研究结果将通过在 2011 年国际地球物理和大地测量联合会会议和 2012 年海洋科学会议上的演讲以及在同行评审期刊上发表的方式在海洋学界传播。