Satellite observations have long revealed to us a spatially growing Kuroshio Extension (KEx), but its underlying dynamics is yet to be studied. With a normal mode model of absolute/convective instability, it is found that the mean zonal jet is unstable at all the sections in the downstream region (east of 154 °E). In each of the resulting complex dispersion relation diagrams there lies a single saddle point associated with a positive temporal growth rate; that is to say, the mean jet is absolutely unstable, implying that KEx favors self-sustained oscillations. By calculation the absolute instability wave has a period increasing from about 27 days to 72 days, and a slightly decreasing wavelength from 360 km to 250 km, as longitude increases from 154 °E to 174 °E, agreeing with those inferred from the wavelet power spectra and Hovmöller diagram of the satellite observations. As KEx travels downstream, the associated eigen-structure of the perturbation velocity changes from a surface trapped mode to a mode with components maximized in the vertical interior. This study shows that at least a portion of the KEx intraseasonal variability is of intrinsic origin, and may be predictable with the absolute/convective instability theory.

卫星观测长期以来一直向我们揭示了空间增长的黑潮扩展（KEx），但其潜在动力学有待研究。利用绝对/对流不稳定性的正常模式模型，发现平均带状射流在下游区域（东154°E以东）的所有区域都是不稳定的。在每个结果复散度关系图中，都存在一个与正的时间增长率相关的鞍点。也就是说，平均射流绝对不稳定，这意味着KEx倾向于自持振荡。通过计算，随着经度从154°E增加到174°E，绝对不稳定波的周期从大约27天增加到72天，波长从360 km略微减小到250 km，与小波功率谱和卫星观测的霍姆维尔图推论得出的结论一致。当KEx向下游移动时，相关的摄动速度的本征结构从表面捕获模式更改为垂直内部成分最大化的模式。这项研究表明，KEx季节内变化的至少一部分是内在起源的，并且可以用绝对/对流不稳定性理论来预测。