To investigate the influences of oceanic intrinsic/internal variability and its interannual-to-decadal modulations on the Kuroshio Extension (KE) jet speed and associated eddy activity, a ten-member ensemble integration of an eddy-resolving ocean general circulation model forced by the 1965–2016 atmospheric reanalysis is conducted. We found a distinct time–scale dependence in the ratio of forced and intrinsic variability of the KE jet speed. On the decadal time scale, the ratio of the magnitude of intrinsic variability to that of the atmospheric–driven variability is 0.73, suggesting it is largely atmospheric–driven. In contrast, on the interannual time scales, the KE jet speed has a large ensemble spread, indicating that it is strongly affected by intrinsic variability and has substantial uncertainty. For eddy activity, the ratios of atmospheric–driven and intrinsic variability also depend on the region. In the downstream KE [32°–38°N, 153°–165°E], variability in the atmospheric–driven eddy activity dominates (1.36 times) over the intrinsic variability on the decadal time scale, and is positively correlated with the current speed. Consistent with the westward propagation of atmospheric–driven jet speed anomalies shown by the ensemble mean, the eddy activity in the downstream KE region is correlated with the current speed variability in the central North Pacific 4 years earlier. This linkage is robust even for each ensemble member with the significant lagged correlation found in seven out of ten ensemble members as well as the ensemble mean (r = 0.59), suggesting the possibility of prediction of the eddy activity. In contrast, the eddy activity in the upstream KE [32°–38°N, 141°–153°E] shows a very large intrinsic and limited atmospheric–driven variability with a ratio of the former to the latter of 2.73. These results suggest that the intrinsic variability needs to be considered in the interannual variability of strong ocean jet. The dependence of these findings to the model specificities needs to be further explored.

中文翻译：

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黑潮延伸射流和涡流活动中的大气驱动和内在年际到年代际变化

为了研究海洋内在/内部变率及其年际到年代际调制对黑潮延伸 (KE) 喷流速度和相关涡流活动的影响，一个由 10 个成员组成的集合集成了一个由1965-2016 年进行了大气再分析。我们发现 KE 喷射速度的受迫变异性和固有变异性的比率存在明显的时间尺度依赖性。在年代际时间尺度上，固有变率与大气驱动变率的大小之比为 0.73，表明它主要受大气驱动。相比之下，在年际时间尺度上，KE 急流速度具有较大的集合展布，表明它受内在变异性的影响很大，具有很大的不确定性。对于涡流活动，大气驱动的变率和内在变率的比率也取决于区域。在下游 KE [32°–38°N, 153°–165°E]，大气驱动的涡旋活动的变化在年代际时间尺度上主导（1.36 倍）内在变化，并与当前正相关速度。与集合平均值显示的大气驱动喷射速度异常向西传播一致，下游 KE 区域的涡旋活动与 4 年前北太平洋中部的当前速度变化相关。即使对于在十个集合成员中的七个中发现显着滞后相关性的每个集合成员以及集合平均值 (r = 0.59)，这种联系也是稳健的，这表明预测涡流活动的可能性。相比之下，上游 KE [32°–38°N, 141°–153°E] 的涡旋活动显示出非常大的内在和有限的大气驱动变化，前者与后者的比率为 2.73。这些结果表明，强洋急流的年际变化需要考虑内在变化。需要进一步探讨这些发现对模型特性的依赖性。