Persistent Turbulence in the Samoan Passage
Persistent Turbulence in the Samoan Passage
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DOI：
10.1175/jpo-d-19-0116.1
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发表时间：
2019-12
影响因子：
3.5
通讯作者：
J. Cusack;Gunnar Voet;M. Alford;J. Girton;G. Carter;L. Pratt;Kelly A. Pearson-Potts;Shuwen Tan
中科院分区：
文献类型：
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作者：
J. Cusack;Gunnar Voet;M. Alford;J. Girton;G. Carter;L. Pratt;Kelly A. Pearson-Potts;Shuwen Tan
形成全球翻转环流下肢的深海水域流经萨摩亚航道，并因强烈混合而发生改变。对部署在两个窗台顶部的系泊剖面仪 17 个月的耗散进行基于索普尺度的估计表明，通道中不断产生湍流。在理查森数通常小于 1/4 的密度带中观察到翻转，这与快速流动的底部水层的上界面处发生的剪切不稳定一致。人们发现耗散量在几周到几个月的长时间范围内是稳定的。第二个阵列由 12 个系泊剖面仪组成，部署时间较短，但剖面分析频率较高，能够解决从几天到几小时的时间尺度上的耗散变化。在一些系泊位置，观察到耗散率的近惯性和潮汐调制。然而，整个通道的调制在空间上并不连贯。将主要基台之一的观测耗散的幅度和垂直结构与包括正压潮汐强迫的理想化二维数值模拟进行比较。模型和观测值之间的深度积分耗散率一致在 3 倍以内。潮汐对平均耗散的影响可以忽略不计。这些观察结果强化了这样一种观念，即萨摩亚海峡是全球海洋中一个重要的混合热点，那里的海水正在不断发生变化。
Abyssal waters forming the lower limb of the global overturning circulation flow through the Samoan Passage and are modified by intense mixing. Thorpe-scale-based estimates of dissipation from moored profilers deployed on top of two sills for 17 months reveal that turbulence is continuously generated in the passage. Overturns were observed in a density band in which the Richardson number was often smaller than ¼, consistent with shear instability occurring at the upper interface of the fast-flowing bottom water layer. The magnitude of dissipation was found to be stable on long time scales from weeks to months. A second array of 12 moored profilers deployed for a shorter duration but profiling at higher frequency was able to resolve variability in dissipation on time scales from days to hours. At some mooring locations, near-inertial and tidal modulation of the dissipation rate was observed. However, the modulation was not spatially coherent across the passage. The magnitude and vertical structure of dissipation from observations at one of the major sills is compared with an idealized 2D numerical simulation that includes a barotropic tidal forcing. Depth-integrated dissipation rates agree between model and observations to within a factor of 3. The tide has a negligible effect on the mean dissipation. These observations reinforce the notion that the Samoan Passage is an important mixing hot spot in the global ocean where waters are being transformed continuously.