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

基于理论、实验室实验和实地观察，峡谷一直被认为是强烈内波的场所。在蒙特利峡谷（MC）的湍流测量和在高平峡谷（台湾）的密度倾覆，具有类似的大小和形状，证实非常强烈的混合。然而，产生混合的过程还没有确定，也没有在足够多的峡谷中测量到混合，以评估其从一个到另一个的可变性。观测和最近的模型表明，内部潮汐是蒙特利峡谷的主要能源来源，它来自近海，也来自当地。此外，沿着峡谷的山脊和狭窄使得背风波和水力跳跃很可能也是混合的主要来源，正如对深海峡谷的推断一样。该项目将对蒙特雷峡谷进行建模和密集观测，并对附近的阿森松峡谷进行勘探，阿森松峡谷比蒙特雷峡谷直得多，显然缺乏重要的近海内部潮汐来源。目标是：1)了解内部潮汐在峡谷中的传播方式，特别是M2能量通量是如何在弯道周围以及转弯太急导致能量耗散的情况下被引导的；2)确定混合的位置和水平是否可以通过沿峡谷M2能量通量的收敛来预测；3)识别和量化由内波散射、背风波和水力跳跃产生的混合；通过测量以外大陆架为终点的相对短而直的峡谷内的混合和内部潮汐，对混合和斜压能的影响。更广泛的ImpactsU.S。海岸上有几十个峡谷，它们几乎占了美国西部大陆斜坡的一半。北到阿拉斯加。虽然峡谷似乎具有丰富的生物资源，并输出水和沉积物，但对峡谷内的动力过程了解甚少，无法对峡谷的重要性进行一般性评估，也无法确定它们是否需要在大尺度或区域模型中进行特殊表示。一组测量不能解决峡谷动力学的所有问题，但提出的工作应该为评估其他峡谷的混合提供定性和定量的基础。如果完全成功，该项目可能无法对某些混合进行参数化，或者至少能够为参数化指明道路。作为提议工作的一部分，研究人员还开始与区域建模者进行谈判，将强烈的峡谷混合纳入模型，并进行灵敏度运行，以确定混合必须有多精确，才能预测其对峡谷外流动和结构的影响。将雇用两名博士后，一名在APL/UW，另一名在夏威夷大学。双方都将参与博士后培养的各个阶段的工作。与蒙特雷湾MBARI定期取样的协调与合作将有利于本项目，反之亦然。外展活动将结合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.