Abstract Based on an eddy-resolving Regional Ocean Modeling System (ROMS) and the conditional nonlinear optimal perturbation (CNOP) method, we set up a nonlinear optimization system to investigate the effects of the fastest-growing initial errors on the prediction of the Kuroshio Extension (KE) transition process from the stable to the unstable state. The results reveal that the larger values of the CNOP-type fastest-growing initial errors are mainly located upstream of the KE over the upper 500 m. Furthermore, the dynamic mechanism of the error growth is explored in terms of error movement, maintenance and development during the KE transition period. The results indicate that the errors are transported eastward from the south of Japan to the KE’s first quasi-stationary meander by linear advection. The nonlinear advection slows down the moving speed of these errors, leading to their long-term existence in the first quasi-stationary meander of the KE. In this situation, errors have enough time to absorb energy from the background field continuously through barotropic energy conversion. Ultimately, errors grow rapidly and further induce the overestimation of the KE strength.

中文翻译：

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涡旋分辨区域海洋模型中黑潮扩展状态转变过程的可预测性和误差增长动力学

摘要 基于涡旋分辨区域海洋建模系统（ROMS）和条件非线性最优扰动（CNOP）方法，我们建立了非线性优化系统，研究增长最快的初始误差对黑潮扩展预测的影响。 (KE) 从稳定状态到不稳定状态的过渡过程。结果表明，CNOP 型增长最快的初始误差的较大值主要位于 KE 上游 500 m 以上。此外，从KE过渡期间的错误移动、维护和发展方面探讨了错误增长的动态机制。结果表明，误差通过线性平流从日本南部向东传输到 KE 的第一个准静止曲流。非线性平流减缓了这些误差的移动速度，导致它们长期存在于 KE 的第一个准平稳曲流中。在这种情况下，误差有足够的时间通过正压能量转换从背景场中不断吸收能量。最终，误差会迅速增长并进一步导致对 KE 强度的高估。