Internal tides are ubiquitously generated from disturbances between barotropic tides and bottom topography in stratified oceans. Incoherence is routinely considered as non-stationary phase discrepancy between internal and astronomical tides. Internal tides, especially incoherent constituents, contribute substantial energy to dissipation and turbulent mixing. Using ∼8-month near-full-depth moored current observations, we investigated internal tides in the Tokara Strait, where the Kuroshio exits the East China Sea. Semidiurnal internal tides, especially the M₂ internal tides, dominate the diurnal internal tides by approximately one-order of magnitude. We decomposed the bandpass-filtered tidal currents into coherent and incoherent constituents, both of which presented a spring–neap cycle; however, the former was largely coupled with local barotropic tides, while the latter had an incoherent phase. The coherent semidiurnal internal tides were intensified and had larger variability near the bottom; nevertheless, the intensity and variability of incoherent internal tides decreased with depth. These results suggest that the incoherent internal tides are exogenous and are possibly affected by the background flow field during propagation. The mean incoherence (above 54 % for both semidiurnal and diurnal internal tides) was expectedly higher than the global mean (∼44 %), implying a robust effect of nonlinear Kuroshio-tide interactions. Moreover, the relationship between the variability of the incoherence and the north–south shift of the Kuroshio further revealed the impact of the background flow intensity variation on internal tides. A ray tracing model demonstrated different refraction indices during the propagation of internal tides, leading to converged (diverged) ray paths in the mooring when the Kuroshio was at the northern (southern) axis position, thus explaining the differential incoherence caused by the variability of the Kuroshio.

内部潮汐普遍存在于分层海洋中正压潮汐和底部地形之间的干扰。不相干通常被认为是内部潮汐和天文潮汐之间的非平稳相位差异。内部潮汐，尤其是不连贯的成分，为耗散和湍流混合提供了大量能量。使用 8 个月的近全深度系泊电流观测，我们调查了黑潮离开东海的 Tokara 海峡的内部潮汐。半日内潮，尤其是 M ₂内部潮汐，在昼夜内部潮汐中占主导地位大约一个数量级。我们将带通滤波的潮汐流分解为连贯和不连贯的成分，两者都呈现出春季-小睡周期；然而，前者主要与当地的正压潮汐耦合，而后者则具有不连贯的阶段。连贯的半日内潮汐增强，在底部附近变化较大；然而，不连贯的内部潮汐的强度和可变性随着深度的增加而降低。这些结果表明，不相干的内部潮汐是外生的，并且可能在传播过程中受到背景流场的影响。平均不连贯性（半日和日内潮汐均高于 54%）预计高于全球平均值（~44%），暗示非线性黑潮相互作用的稳健效应。此外，不相干性变化与黑潮南北偏移的关系进一步揭示了背景流强度变化对内部潮汐的影响。射线追踪模型显示了内部潮汐传播过程中不同的折射率，导致当黑潮位于北（南）轴位置时，系泊中的射线路径会聚（发散），从而解释了由海潮变化引起的差异不相干性。黑潮。