Mixing and Transformation in a Deep Western Boundary Current: A Case Study
Mixing and Transformation in a Deep Western Boundary Current: A Case Study
复制标题
西部深层边界流中的混合与转变：案例研究
DOI：
10.1175/jpo-d-20-0132.1
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发表时间：
2021
影响因子：
3.5
通讯作者：
Spingys Carl P.
中科院分区：
文献类型：
--
作者：
Spingys Carl P.
湍流混合引起的水团转化是深海翻转的关键部分，因为它驱动高纬度地区形成的稠密水域的上涌。在这里，我们量化了南大洋小盆地奥克尼深海的这种转变及其基础过程。观测结果揭示了当深西边界流（DWBC）流经该区域时，密度空间中的传输集中，分别与电流较密层和较轻层的变轻和致密化相关。这些转变是由剧烈的湍流混合驱动的。将该变换与湍流动能耗散率的测量值进行比较表明，在 DWBC 内，湍流以高混合效率运行，其特点是耗散比为 0.6 比 1，超过了常见值 0.2。通过微观结构观察对耗散比的估计证实了这一结果。通过分解依赖于密度空间梯度的贡献，揭示了转变的原因：二中性混合速率、等中性面积和分层。研究发现，这种转变主要是由强湍流驱动的，该湍流作用于从弱分层底部边界层到分层良好的边界水域的突然过渡。边界层层化的减少是由与 DWBC 沿倾斜地形的流动相关的下坡埃克曼流产生的，并受到亚中尺度不稳定性的进一步调节，这些不稳定作用使近边界水域重新分层。我们的研究结果提供了观测证据，证实了近边界混合过程对深海翻转的重要性，并强调了 DWBC 作为双中性上升流热点的作用。
Water-mass transformation by turbulent mixing is a key part of the deep-ocean overturning, as it drives the upwelling of dense waters formed at high latitudes. Here, we quantify this transformation and its underpinning processes in a small Southern Ocean basin: the Orkney Deep. Observations reveal a focusing of the transport in density space as a deep western boundary current (DWBC) flows through the region, associated with lightening and densification of the current’s denser and lighter layers, respectively. These transformations are driven by vigorous turbulent mixing. Comparing this transformation with measurements of the rate of turbulent kinetic energy dissipation indicates that, within the DWBC, turbulence operates with a high mixing efficiency, characterized by a dissipation ratio of 0.6 to 1 that exceeds the common value of 0.2. This result is corroborated by estimates of the dissipation ratio from microstructure observations. The causes of the transformation are unraveled through a decomposition into contributions dependent on the gradients in density space of the: dianeutral mixing rate, isoneutral area, and stratification. The transformation is found to be primarily driven by strong turbulence acting on an abrupt transition from the weakly stratified bottom boundary layer to well-stratified off-boundary waters. The reduced boundary layer stratification is generated by a downslope Ekman flow associated with the DWBC’s flow along sloping topography, and is further regulated by submesoscale instabilities acting to restratify near-boundary waters. Our results provide observational evidence endorsing the importance of near-boundary mixing processes to deep-ocean overturning, and highlight the role of DWBCs as hot spots of dianeutral upwelling.
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影响因子：
3.5
作者：
H. Drake;R. Ferrari;J. Callies
通讯作者：
H. Drake;R. Ferrari;J. Callies
DOI：
10.3402/tellusa.v34i2.10801
发表时间：
1982-04
期刊：
Tellus A
影响因子：
--
作者：
G. Walin
通讯作者：
G. Walin
影响因子：
3.5
作者：
Iudicone, Daniele;Madec, Gurvan;McDougall, Trevor J.
通讯作者：
McDougall, Trevor J.
DOI：
10.17863/cam.9670
发表时间：
2017
期刊：
--
影响因子：
--
作者：
Caulfield C
通讯作者：
Caulfield C
影响因子：
3.5
作者：
de Lavergne, Casimir;Madec, Gurvan;Garabato, Alberto C. Naveira
通讯作者：
Garabato, Alberto C. Naveira