Collaborative Research: The Internal Tide and Mixing in Monterey and Ascension Canyons

学术价值基于理论、实验室实验和野外观察，峡谷长期以来被认为是强烈内波的场所。蒙特利峡谷（MC）的湍流测量和高屏峡谷（台湾）的密度反转，具有相似的大小和形状，证实了非常强的混合。然而，产生混合的过程尚未确定，也没有在足够的峡谷中测量混合，以评估其从一个到另一个的变化。观测和最近的模拟表明，内潮是蒙特雷峡谷的主要能量来源，既来自近海，也来自当地。此外，沿着峡谷的山脊和收缩使得背风波和水跃可能也是混合的主要来源，正如对深海峡谷所推断的那样，该项目将对蒙特雷峡谷进行建模和深入观察，并对附近的Ascension峡谷进行勘探，该峡谷比蒙特雷直得多，显然缺乏重要的内潮离岸来源。目标是：1）了解内潮如何在峡谷中传播，特别是M2能量通量如何在弯道周围转向，以及何时转弯如此尖锐以至于能量被耗散，2）确定是否可以通过沿峡谷M2能量通量的收敛来预测混合位置和水平，3）识别和量化由内波散射、背风波和水力跃变产生的混合，4）通过测量终止于外大陆架的相对较短的直峡谷中的混合和内潮，评估峡谷的形状、平滑度和与近海M2源对齐对混合和斜压能量的影响。海岸有几十个峡谷，它们几乎占了从北纬45度到阿拉斯加的西大陆坡的一半。虽然它们似乎是生物丰富和出口的水和沉积物，峡谷内的动力学过程知之甚少，使峡谷的重要性或他们是否需要在大规模或区域模型的特殊代表性的一般评估。一套测量不能解决所有关于峡谷动力学的问题，但拟议的工作应提供定性和定量的基础，以评估在其他峡谷的混合。如果完全成功，这个项目可能无法参数化的一些混合或至少能够指出的方式参数化。作为拟议工作的一部分，调查人员还开始与区域建模人员进行会谈，将强烈的峡谷混合纳入模型，并进行灵敏度试验，以确定混合必须有多准确，以预测其对峡谷外流动和结构的影响。两名博士后将被雇用，一个在APL/UW，另一个在夏威夷大学。两人都将参与博士后培养的各个阶段的工作。与蒙特雷湾MBARI定期采样的协调和合作将有利于这个项目，反之亦然。推广活动将结合联合收割机早期的峡谷测量和未来的测量。

Intellectual MeritBased on theory, laboratory experiments and field observations, canyons have long been identified as sites of intense internal waves. Turbulence measurements in Monterey Canyon (MC) and density overturns in Kaoping Canyon (Taiwan), which has similar size and shape, confirm very strong mixing. The processes generating the mixing, however, have not been determined, nor has mixing been measured in enough canyons to assess its variability from one to another. Observations and recent modeling indicate that the internal tide is a major source of energy in Monterey Canyon, coming from offshore as well as being generated locally. In addition, ridges and constrictions along the canyon make it likely that lee waves and hydraulic jumps are also major sources of mixing, as has been inferred for abyssal canyons.The project will undertake modeling and intensive observations for Monterey Canyon and exploration of nearby Ascension Canyon which is much straighter than Monterey and apparently lacks a significant offshore source for the internal tide. The goals are to: 1) understand how the internal tide propagates in canyons, and in particular how the M2 energy flux is steered around bends and when turns are so sharp that the energy is dissipated, 2) determine whether mixing locations and levels can be predicted by convergences in the along-canyon M2 energy flux, 3) identify and quantify mixing produced by internal wave scattering, lee waves and hydraulic jumps, and 4) assess the effects that canyon shape, smoothness and alignment with offshore M2 sources have on mixing and baroclinic energy by measuring mixing and the internal tide in a relatively short, straight canyon ending on the outer shelf.Broader ImpactsU.S. coasts have dozens of canyons, and they account for almost half of the western continental slope from 45◦N to Alaska. Though they appear to be biologically rich and export both water and sediments, dynamical processes within canyons are too poorly understood to make a general assessment of the importance of canyons or whether they require special representation in large-scale or regional models. One set of measurements cannot resolve all questions about canyon dynamics, but the proposed work should provide qualitative and quantitative bases for assessing mixing in other canyons.. If fully successful, this project may unable the parameterization of some of the mixing or at least be able to point the way to parameterizations. As part of the proposed effort the investigators have also begun talks with regional modelers to incorporate intense canyon mixing into the models and to do sensitivity runs to define how accurately the mixing must be known to predict its effect on flows and structures outside the canyon. Two post-doc will be hired, one at APL/UW and another at the University of Hawaii. Both willparticipate in all phases of the work for their postdoctoral training. Coordination and collaboration with the regular MBARI sampling of Monterey Bay will benefit this project, and vice versa. Outreach activities will combine earlier canyon measurements and the future measurements.