| 摘要: |
| 基于正压出入流模式, 利用条件非线性最优扰动(CNOP)方法研究初始异常的位置与模态对日本南部黑潮路径变异的影响。以模式模拟出的黑潮平直路径的平衡态作为参考态, 计算CNOP, 考察该扰动随时间的发展, 并与随机扰动的发展进行对比。结果表明, CNOP 能够导致黑潮弯曲路径发生, 随机扰动则不能。因此, CNOP 可以作为导致日本南部黑潮路径发生弯曲的一种最优前期征兆。通过分析CNOP 和随机扰动的发展过程, 可以得出: (1) CNOP 使黑潮发展成弯曲路径的过程是一个气旋涡向下游传播并增长的过程。(2) 气旋涡的向东传播都是非线性项的作用, 也就是涡度平流造成的。(3) CNOP和随机扰动发展过程中所产生的气旋涡均会传播到下游区域, 但是CNOP 产生的气旋涡能够增强, 最终导致弯曲路径发生, 而随机扰动产生的气旋涡则会减弱, 并不能导致弯曲路径发生。分析发现, 在CNOP 实验中, 非线性作用使气旋涡增大; 但在随机扰动实验中, 非线性作用使气旋涡减弱, 所以非线性作用对日本南部黑潮路径发生弯曲有重要影响。(4) 底摩擦效应对日本南部黑潮路径变异影响较小。本文揭示的黑潮路径发生弯曲的最优前期征兆及其非线性发展机制, 对提高黑潮路径变异的预报技巧具有重要意义。 |
| 关键词: 黑潮路径 条件非线性最优扰动(CNOP) 前期征兆 正压出入流模式 |
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| 基金项目:中国科学院知识创新工程重要方向项目(KZCX2-EW-201);青岛市基础研究计划项目(11-1-4-95-jch); 中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室(LASG)开放课题 |
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| The optimal precursor of the occurrence of the Kuroshio meander path in the south of Japan and its development mechanism |
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| Abstract: |
| The barotropic inflow-outflow model was built to study the impacts of spatial locations and patterns of the initial anomaly on the variability of the Kuroshio path using the conditional nonlinear optimal perturbation (CNOP) method. First, the CNOP was calculated using the equilibrium of the straight path as reference state. Then the CNOP was superimposed on the reference state to investigate its development process, which was compared with the evolutions of random perturbation (RP). We found that the CNOP caused the Kuroshio path to transfer to meander path while the random perturbation did not. In this case, the CNOP could be regarded as the optimal precursor of the Kuroshio meander path. By analyzing the developing processes of the CNOP and the RP, we concluded that: 1) The formation process of the Kuroshio meander path caused by CNOP was the process of a cyclonic eddy advection downstream. 2) The cyclonic eddy was transferred to downstream due to the effect of nonlinear items, which was also the vorticity advection term. 3) The eddies both in the CNOP and RP cases would transport to the downstream, but the eddy in the CNOP case could grow up and develop into meander path while the eddy in the RP case could not. The cyclonic eddy was strengthened by the nonlinear effect in the CNOP case, while it was weakened by the nonlinear effect in the RP case. In conclusion, the nonlinear effect was very important in the processes of the formation of the Kuroshio meander path in the south of Japan. 4) The impact of bottom friction has relatively small effeots on the variability of the Kuroshio path in the south of Japan. This study has revealed the optimal precursor of the occurrence of Kuroshio meander path and its nonlinear evolution mechanism, which is very important for improving the forecast skill of the Kuroshio path variations. |
| Key words: the Kuroshio path conditional nonlinear optimal perturbation (CNOP) optimal precursor barotropic inflow-outflow model |
