Tidal Conversion and Mixing Poleward of the Critical Latitude (an Arctic Case Study)
Tidal Conversion and Mixing Poleward of the Critical Latitude (an Arctic Case Study)
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DOI：
10.1002/2017gl075310
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发表时间：
2017-12-28
影响因子：
5.2
通讯作者：
Bacon, Sheldon
中科院分区：
文献类型：
--
作者：
Rippeth, Tom P.;Vlasenko, Vasiliy;Bacon, Sheldon
潮汐是支持全球海洋湍流混合的动能的主要来源。潮汐能向湍流混合的转移的主要机制是地形和分层潮流之间的相互作用，导致在强迫潮期间产生自由传播的内波。然而，在临界纬度（主分潮的周期超过当地惯性周期）的极向，科里奥利力的作用排除了自由传播的线性内潮的发展。在这里，我们集中在一个地区的斜坡地形，极地的临界纬度，有显着的转换潮汐能和流量是超临界（弗劳德数，Fr > 1）。高分辨率的非线性模拟研究表明，潮汐产生的背风波和超临界流的能量从正压潮汐在这些高纬度地区的内波转移的关键作用。感兴趣的区域的流量和水柱结构的时间序列显示内波的特性与模型预测的一致，并发的微观结构耗散测量显示与这些内波相关的混合的显着水平。结果表明，潮汐产生的背风波是能量从潮汐向临界纬度极向湍流转移的关键机制。简明语言摘要近年来覆盖北冰洋的海冰的空中范围的减少可能是气候变化的主要迹象之一。温暖的海水在100- 200米深处进入北冰洋;然而，由于北冰洋缺乏混合，它与融化的冰隔离开来。这种混合的缺乏被归因于海洋被冰与风隔离，以及北冰洋的大部分位于临界纬度以北的事实，超过这个纬度，被认为可以驱动地球上其他主要海洋混合的内潮类型就不会发生。然而，新的证据表明，潮汐可能对推动北冰洋某些地区的混合很重要。在这里，我们结合联合收割机国家的最先进的数值模拟与新的湍流测量，以确定潮汐可以驱动混合在这些高纬度地区的机制。
The tides are a major source of the kinetic energy supporting turbulent mixing in the global oceans. The prime mechanism for the transfer of tidal energy to turbulent mixing results from the interaction between topography and stratified tidal flow, leading to the generation of freely propagating internal waves at the period of the forcing tide. However, poleward of the critical latitude (where the period of the principal tidal constituent exceeds the local inertial period), the action of the Coriolis force precludes the development of freely propagating linear internal tides. Here we focus on a region of sloping topography, poleward of the critical latitude, where there is significant conversion of tidal energy and the flow is supercritical (Froude number, Fr > 1). A high-resolution nonlinear modeling study demonstrates the key role of tidally generated lee waves and supercritical flow in the transfer of energy from the barotropic tide to internal waves in these high-latitude regions. Time series of flow and water column structure from the region of interest show internal waves with characteristics consistent with those predicted by the model, and concurrent microstructure dissipation measurements show significant levels of mixing associated with these internal waves. The results suggest that tidally generated lee waves are a key mechanism for the transfer of energy from the tide to turbulence poleward of the critical latitude.Plain Language Summary The decline in aerial extent of sea ice covering the Arctic Ocean in the recent years is perhaps one of the leading indications of climate change. Warm water enters the Arctic Ocean at depths of 100-200m; however, it is isolated from melting the ice by the lack of mixing in the Arctic Ocean. This lack of mixing has been attributed to the ocean being isolated from the wind by ice, and the fact that much of the Arctic Ocean is north of the critical latitude, beyond which the type of internal tide that is believed to drive mixing across other major oceans on the planet cannot occur. However, new evidence has been found that suggests that the tide might be important in driving mixing in certain areas of the Arctic Ocean. Here we combine state-of-the-art numerical modeling with new turbulence measurements to identify the mechanism by which the tide can drive mixing at these high latitudes.