Semidiurnal internal tide incoherence in the equatorial Pacific
Semidiurnal internal tide incoherence in the equatorial Pacific
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DOI：
10.1002/2016jc012590
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发表时间：
2017-07-01
影响因子：
3.6
通讯作者：
Zamudio, Luis
中科院分区：
文献类型：
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作者：
Buijsman, Maarten C.;Arbic, Brian K.;Zamudio, Luis
在一个水平分辨率为1/12.5度的实际强迫全球环流模式中，赤道太平洋的急流导致了从法属波利尼西亚群岛和夏威夷向赤道传播的半日内潮的相位相干性的强烈丧失。这种相干性的损失是用斜压能量分析来量化的，在斜压能量分析中，半日波段项被分成相干项、非相干项和交叉项。对于超过一年的时间尺度，赤道的相干能量通量接近于零值，而总通量接近于500 W/m。将非相干能量通量的时间变异性与基于Taylor-Goldstein方程计算的沿波束积分相速计算的内潮汐行时变异性进行了比较。月平均Taylor-Goldstein相速的变率与平面波拟合技术提取的海面高度位相推断的相速变率吻合较好。在月时间尺度上，来自法属波利尼西亚群岛的赤道方向波束的相位相干性丧失归因于与喷流和热带不稳定波有关的垂直剪切背景流的时间变化。在年时间尺度上，分层变率的影响与切变率对相干性丧失的影响同等或更重要。在模式模拟中，低频赤道喷流对内潮的耗散没有明显的增强作用，而只是消相干和散射。
The jets in the equatorial Pacific Ocean of a realistically forced global circulation model with a horizontal resolution of 1/12.5 degrees cause a strong loss of phase coherence in semidiurnal internal tides that propagate equatorward from the French Polynesian Islands and Hawaii. This loss of coherence is quantified with a baroclinic energy analysis, in which the semidiurnal-band terms are separated into coherent, incoherent, and cross terms. For time scales longer than a year, the coherent energy flux approaches zero values at the equator, while the total flux is similar to 500 W/m. The time variability of the incoherent energy flux is compared with the internal-tide travel-time variability, which is based on along-beam integrated phase speeds computed with the Taylor-Goldstein equation. The variability of monthly mean Taylor-Goldstein phase speeds agrees well with the phase speed variability inferred from steric sea surface height phases extracted with a plane-wave fit technique. On monthly time scales, the loss of phase coherence in the equatorward beams from the French Polynesian Islands is attributed to the time variability in the vertically sheared background flow associated with the jets and tropical instability waves. On an annual time scale, the effect of stratification variability is of equal or greater importance than the shear variability is to the loss of coherence. In the model simulations, low-frequency equatorial jets do not noticeably enhance the dissipation of the internal tide, but merely decohere and scatter it.