| 基于自组织映射的日本南部黑潮与黑潮延伸体的典型时空模态及其因果关系研究 |
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| 引用本文： | 吴友婷,杨洋,梁湘三.基于自组织映射的日本南部黑潮与黑潮延伸体的典型时空模态及其因果关系研究[J].海洋学报,2022,44(9):38-54. |
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| 作者姓名： | 吴友婷 杨洋 梁湘三 |
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| 作者单位： | 1.自然资源部第一海洋研究所 海洋环境科学与数值模拟重点实验室，山东 青岛 266061 |
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| 基金项目： | 国家自然科学基金（41806023，41975064）；2015江苏双创团队项目；上海市“科技创新行动计划”国际科技合作伙伴项目（21230780200）。 |
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| 摘 要： | 过去的研究认为，黑潮延伸体的年代际振荡受来自其下游的太平洋年代际振荡（PDO）相关联的信号主导，但最近的观测表明这种调控机制在2017年9月之后不再成立。与此同时，黑潮延伸体的上游即日本南部黑潮正在发生一次大弯曲事件。利用26年（1993–2018年）的卫星高度计提供的海表高度距平数据和自组织映射（SOM）方法，本文研究了日本南部黑潮与黑潮延伸体的时空模态及其因果关系。结果表明，SOM能有效地提取两个海区的典型空间模态，且它们的演变轨迹表明当日本南部黑潮处于大弯曲（离岸型非大弯曲）路径时，黑潮延伸体趋于稳定（不稳定）态。基于SOM识别得到的海表面高度距平（SLA）特征区及特征时间模态，我们进一步利用一种最近发展的定量因果分析方法研究了两个流系之间的因果关系。研究发现，当黑潮大弯曲发生时，日本南部黑潮和黑潮延伸体之间存在双向因果，但因果关键区不同。前者对后者的影响集中在纪伊半岛东南侧及黑潮延伸体“两脊一槽”区域，而后者对前者的影响则集中在黑潮延伸体“两脊一槽”区域及黑潮再循环流区域。这说明黑潮大弯曲的发展对黑潮延伸体的稳定性有重要作用，同时黑潮延伸体通过调制南部再循环流影响日本南部黑潮的路径。不同的是，当离岸型非大弯曲路径发生时，只有从日本南部黑潮向黑潮延伸体的单向因果关系，且因果性主要集中在伊豆海脊及再循环流区域。这与该时期海表高度负异常沿日本南岸不断向位于下游的黑潮延伸体再循环流的传播有关，它使得黑潮延伸体变得不稳定。
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| 关 键 词： | 黑潮大弯曲 黑潮延伸体 自组织映射 因果分析 信息流 |
| 收稿时间： | 2021-10-12 |
Typical spatiotemporal patterns of the Kuroshio south of Japan and the Kuroshio extension using self-organizing maps and their causal relationship |
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| Abstract: | Previous studies have shown that the decadal modulation of the Kuroshio extension (KE) system is controlled by the Pacific decadal oscillation-associated forcing from downstream. However, recent observation reveals that this mechanism ceases to function after August 2017. Meanwhile, a large meander is under development in the KE’s upstream, i.e., south of Japan. Using the self-organizing map (SOM), we investigate the characteristic spatial and temporal patterns of the Kuroshio south of Japan and the KE and their causal relations, based on the 26-year (1993?2018) satellite altimetry data of sea level anomaly (SLA). The typical spatial patterns are well extracted, and their temporal trajectories indicate that the KE tends to be stable (unstable) when the upstream Kuroshio takes a large meander (an offshore nonlarge meander) path. To further unravel the underlying cause-and-effect relation between the two systems, we apply the information flow-based causality analysis to the typical regions of SLA and its associated temporal modes identified with the SOM. It is found that during the large meander event, the Kuroshio south of Japan and the KE are mutually causal, but have different hotspots. The information flows from the former to the latter mainly occur in the southeastern area off the Kii Peninsula and the time-mean ridge and trough of the KE jet, while those from the latter to the former are mainly concentrated in the time-mean ridge and trough of the KE jet, and the recirculation gyre of the Kuroshio. These results indicate that the Kuroshio large meander is an important factor influencing the KE’s stability, while the KE affects its upstream Kuroshio via modulating the associated recirculation gyres. In contrast, when the offshore nonlarge meander path is taken, a one-way causality is identified from the Kuroshio to the KE, mainly occurring over the Izu-Ogasawara Ridge and in the recirculation gyres. This may be attributed to the constantly downstream transport of negative SLAs into the KE’s recirculation gyre, which leads to an unstable KE. |
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