初始误差对黑潮延伸体年代际变异预测的影响及其机制

Decadal variability of the Kuroshio extension has important effects on weather, climate, ocean ecosystem and fisheries. It is of great significance to study the predictability of the decadal variability of the Kuroshio extension. Both the anomalous wind stress of the atmosphere and the internal nonlinear physical processes of the ocean impact the decadal variability of the Kuroshio extension. But the previous predictability studies about the decadal variability of the Kuroshio extension only considered the effect of the anomalous wind stress or the nonlinear physical processes. In this study, we will consider the combined effects of the above two aspects to investigate the predictability of the decadal variability of the Kuroshio extension using the conditional nonlinear optimal perturbation (CNOP) method. Specifically, the effects of the initial error on the prediction of the decadal variability of the Kuroshio extension will be quantitatively assessed. The evolution processes of the initial error will be investigated. The dynamic mechanism of the combined effects of the anomalous wind stress and the nonlinear physical processes on the initial error growth which could impact the prediction results will be revealed. This study will be helpful to clarify the reason and mechanism resulting in the prediction uncertainties of the decadal variability of the Kuroshio extension and provide a scientific guidance for enhancing the forecast skills of the decadal variability of the Kuroshio extension.

黑潮延伸体年代际变异对天气、气候、海洋生态和渔业生产等有重要影响，所以开展其可预测性研究具有重要意义。大气的异常风应力和海洋内在的非线性物理过程均对黑潮延伸体年代际变异产生影响，而前人关于黑潮延伸体年代际变异的可预测性研究要么仅考虑异常风应力的影响，要么仅考虑非线性物理过程的影响，本项目将同时考虑上述两个方面的影响，利用条件非线性最优扰动方法开展黑潮延伸体年代际变异的可预测性研究。具体地，定量地评估初始误差对黑潮延伸体年代际变异预测的影响，考察初始误差的发展演变过程，揭示异常风应力和非线性物理过程的共同作用影响初始误差发展进而影响预测结果的动力机制。本项目的实施有助于弄清导致黑潮延伸体年代际变异预测不确定性的原因和机制，为提高其预测技巧提供科学指导。

黑潮延伸体在年代际时间尺度上展现了两种状态：拉伸状态和收缩状态，本项目利用非线性最优化方法考察了这两种状态之间相互转变过程的可预报性，首先，建立了用于研究黑潮延伸体可预报性的非线性优化系统，然后利用该系统计算得到了对黑潮延伸体状态转变过程预报影响最大的初始误差，其具有局地性结构特征：大值主要位于黑潮延伸体区域和日本南部区域。通过考察误差的发展，发现当黑潮延伸体从收缩状态转变为拉伸状态时，误差发展较慢，而对于相反的转变过程，误差发展较快，这表明收缩状态向拉伸状态的转变过程比相反的转变过程更容易预报。机理研究发现，对于从收缩状态向拉伸状态的转变过程，误差发展主要由局地不稳定过程引起，而对于相反的转变过程，误差发展主要由平流过程，尤其是非线性平流过程导致。同时，本项目还调查了不同风应力对初始误差空间结构及其发展的影响，结果发现风应力的影响较弱。本项目成果为提高黑潮延伸体的预报技巧提供了科学支撑，并且其所揭示的初始误差的局地性特征对设计黑潮延伸体的最优观测网具有重要的指导意义。