Small-Scale Potential Vorticity in the Upper-Ocean Thermocline
Small-Scale Potential Vorticity in the Upper-Ocean Thermocline
复制标题
上层海洋温跃层的小尺度位涡
DOI：
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发表时间：
2019
影响因子：
3.5
通讯作者：
T. Sanford
中科院分区：
文献类型：
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作者：
R. Lien;T. Sanford
夏季马尾藻海上层海洋温跃层的20个电磁自主廓线探测器(EM-APEX)观测了厄特尔位涡(PV)在7-70m垂直尺度上的时间和垂直变化，在O(4-8)公里水平尺度上的平均变化。PV由其线性分量-垂直涡度和涡旋伸展-主导，每一个分量的均方根值为~0.15f。在内波频段，它们是相干的和同相的，正如线性内波所预期的那样。强的，>；0.2F，垂直涡度和涡旋伸展的分组与一个小的净均方根PV紧密平衡。PV谱在最高可分辨垂直波数~0.1cpm处出现峰值。光伏频谱具有红色光谱形状，在内波频段具有−-1谱斜率，在惯性频率处有一个小峰值。在近惯性频率下测量的PV部分归因于浮子测量的非拉格朗日性质。测量误差和涡旋模式也对内波频段的PV有影响。利用垂直涡度和涡旋伸展的时间变化率计算的涡模Burger数为0.2-0.4，意味着水平动能与有效势能之比约为0.1。涡旋模能谱比观测能谱小1-20年。涡旋模式的能量可能被低估了，因为它在垂直尺度>；70米的能量没有被测量到。涡旋模式占总能量比随着垂直波数的增加而增大，这意味着它在小垂直尺度上的重要性。
Twenty Electromagnetic Autonomous Profiling Explorer (EM-APEX) floats in the upper-ocean thermocline of the summer Sargasso Sea observed the temporal and vertical variations of Ertel potential vorticity (PV) at 7–70-m vertical scale, averaged over O(4–8)-km horizontal scale. PV is dominated by its linear components—vertical vorticity and vortex stretching, each with an rms value of ~0.15f. In the internal wave frequency band, they are coherent and in phase, as expected for linear internal waves. Packets of strong, >0.2f, vertical vorticity and vortex stretching balance closely with a small net rms PV. The PV spectrum peaks at the highest resolvable vertical wavenumber, ~0.1 cpm. The PV frequency spectrum has a red spectral shape, a −1 spectral slope in the internal wave frequency band, and a small peak at the inertial frequency. PV measured at near-inertial frequencies is partially attributed to the non-Lagrangian nature of float measurements. Measurement errors and the vortical mode also contribute to PV in the internal wave frequency band. The vortical mode Burger number, computed using time rates of change of vertical vorticity and vortex stretching, is 0.2–0.4, implying a horizontal kinetic energy to available potential energy ratio of ~0.1. The vortical mode energy frequency spectrum is 1–2 decades less than the observed energy spectrum. Vortical mode energy is likely underestimated because its energy at vertical scales > 70 m was not measured. The vortical mode to total energy ratio increases with vertical wavenumber, implying its importance at small vertical scales.