Temporal Characteristics of Abyssal Finescale Motions above Rough Bathymetry
Temporal Characteristics of Abyssal Finescale Motions above Rough Bathymetry
复制标题
粗略测深以上深渊细尺度运动的时间特征
DOI：
10.1175/jpo2988.1
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发表时间：
2007
影响因子：
3.5
通讯作者：
J. Toole
中科院分区：
文献类型：
--
作者：
J. Toole
本文报道了南大西洋中大西洋海脊西侧断裂带内两年系泊的海流计数据。与巴西盆地示踪剂释放实验一起部署的系泊装置被放置在以前推断出增强的贯入混合的一般区域。流速计数据表征速度、温度、剪切和温度梯度变化作为频率的函数。在系泊处观察到各种频率的高能速度和剪切。除了半日流，大量的剪切方差来自近惯性运动，已经看到在最近的潮汐频率内波辐射和波波相互作用的数值模拟研究。有时，数据中显示出总的超惯性切变方差每两周一次的调制，但这种信号并没有主导记录。波射线追踪表明，较深的流速计可能被放置在阴影区，用于当地产生的内潮。在较浅的水平，它被认为是分散，波-波相互作用，和波破碎有效地掩盖了细尺度能量的来源。平均diapycnal扩散率估计推断从Richardson数为基础的参数化和温度逆温在4648米的观测是相同的数量级来自湍流耗散估计和diapycnal示踪剂分散率。因此，系泊数据增加了额外的支持的想法，有力的细尺度运动以上粗糙测深支持增强湍流diapycnal混合在这些地区。
Current-meter data from a two-year mooring within a fracture zone on the western flank of the MidAtlantic Ridge in the South Atlantic Ocean are reported. The mooring, deployed in conjunction with the Brazil Basin Tracer Release Experiment, was placed in the general area where enhanced diapycnal mixing had previously been inferred. The current-meter data characterize the velocity, temperature, shear, and temperature gradient variability as a function of frequency. Energetic velocities and shears were observed at the mooring at a variety of frequencies. In addition to semidiurnal flows, a significant amount of shear variance derived from near-inertial motions, as has been seen in a recent numerical modeling study of tidal-frequency internal wave radiation and wave–wave interaction. At times, a fortnightly modulation of the total superinertial shear variance was indicated in the data, but this signal did not dominate the records. Wave ray tracing indicates that the deeper current meters may have been placed in a shadow zone for locally generated internal tides. At shallower levels, it is suggested that dispersion, wave–wave interaction, and wave breaking effectively obscured the sources of the finescale energy. Average diapycnal diffusivity estimates inferred from a Richardson-number-based parameterization and from observations of temperature inversions at 4648 m were of the same order of magnitude as those derived from turbulent dissipation estimates and from the rate of diapycnal tracer dispersion. The mooring data thus add additional support to the idea that energetic finescale motions above rough bathymetry support enhanced turbulent diapycnal mixing in these regions.