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首页> 外文期刊>Journal of Physical Oceanography >A Kuroshio Extension System Model Study: Decadal Chaotic Self-Sustained Oscillations
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A Kuroshio Extension System Model Study: Decadal Chaotic Self-Sustained Oscillations

机译：黑潮扩展系统模型研究：十进制混沌自持振荡

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摘要

A model study of the Kuroshio Extension system, in which forcing is provided by a time-independent climatological wind, yields a mean meandering path and a decadal variability of the jet in significant agreement with in situ and altimetric measurements. A reduced-gravity primitive equation ocean model is implemented in a box spanning the whole North Pacific, including a schematic coastline at the western side, and an analytical wind forcing is determined according to the ECMWF and Comprehensive Ocean-Atmosphere Data Set (COADS) climatologies. The modeled time-averaged Kuroshio Extension shows meanders, northern and southern recirculation regions, and a jet penetration that are in good agreement with the corresponding observed climatological features. This result suggests that intrinsic nonlinear mechanisms are likely to play a major role in determining the meander pattern of the mean flow. The internal low-frequency variability is found to be a chaotic bimodal self-sustained oscillation between an energetic meandering state and a much weaker state with a reduced zonal penetration of the jet. These high and low energy states are found to be very similar to the "elongated" and "contracted" modes of the Kuroshio Extension detected through altimetric measurements; moreover, the characteristic period (of around 10 yr), flow patterns, and transition details of a typical bimodal cycle are found to be in significant agreement with altimeter observations for the period 1992-2004. A complex dynamical mechanism supporting this internal oscillation, and involving the bimodal behavior of the Kuroshio south of Japan, is proposed and discussed. On the basis of these modeling results and of their validation with altimeter data, it is hypothesized that the observed bimodal decadal variability of the Kuroshio Extension is basically due to a self-sustained internal oscillation related to the instability of the Kuroshio south of Japan without any crucial intervention of wind-driven Sverdrup transport fluctuations and of topographic interactions, although such effects certainly play an important role in shaping the finer structure of Kuroshio Extension changes. Finally, in a preliminary analysis of the variability in the framework of nonlinear dynamical systems theory it is suggested that the strange attractor corresponding to the modeled low-frequency variability is associated with a homoclinic orbit produced by a global bifurcation; moreover, transitions between oscillations of different character found for slightly different values of the lateral eddy viscosity and forcing amplitude are conjectured to be due to heteroclinic connections.
机译：对黑潮扩展系统进行的模型研究表明，与时间无关的气候风提供了强迫作用，产生了平均的蜿蜒路径和射流的年代际变化，这与原位和高程测量结果非常吻合。在横跨整个北太平洋的盒子中实现了一个重力降低的原始方程海洋模型，包括在西侧的示意性海岸线，并根据ECMWF和综合海洋大气数据集（COADS）气候确定了分析风强迫。 。建模的时间平均黑潮扩展显示出蜿蜒曲折的区域，北部和南部的回流区域以及射流的穿透力，与相应的观测气候特征非常吻合。该结果表明，固有的非线性机制可能在确定平均流的曲折模式中起主要作用。内部低频变化被发现是在高能曲折状态和弱得多的状态之间的混沌双峰自持振荡，射流的区域穿透减少。这些高能态和低能态与通过测高法检测到的黑潮扩展的“伸长”和“收缩”模式非常相似。此外，典型的双峰周期的特征周期（约10年），流型和过渡细节与1992-2004年的高度计观测结果非常一致。提出并讨论了支持这种内部振荡并涉及日本南部黑潮的双峰行为的复杂动力学机制。根据这些建模结果以及用高度计数据进行的验证，假设观察到的黑潮扩展的双峰年代际变化基本上是由于与日本南部黑潮的不稳定性有关的自我维持的内部振荡所致。风驱动的Sverdrup输运波动和地形相互作用的关键干预措施，尽管这种影响在塑造黑潮延期变化的精细结构中当然起着重要作用。最后，在非线性动力学系统理论框架内对变异性的初步分析中，建议与模型化的低频变异性相对应的奇异吸引子与整体分叉产生的同斜轨道有关。此外，可以推测，由于横向涡粘度和强迫振幅略有不同，在不同特性的振荡之间的过渡是由于异斜面连接引起的。

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  • 来源
    《Journal of Physical Oceanography》 |2006年第8期|p.1605-1625|共21页
  • 作者

    STEFANO PIERINI;

  • 作者单位

    Dipartimento di Scienze per l'Ambiente, Universita di Napoli 'Parthenope,' Via A. De Gasperi, 5-80133 Napoli, Italy;

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  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 海洋学;
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