Typical spatiotemporal patterns of the Kuroshio south of Japan and the Kuroshio extension using self-organizing maps and their causal relationship

Wu Youting; Yang Yang; Liang Xiangsan

doi:10.12284/hyxb2022069

Volume 44 Issue 9

Aug. 2022

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Article Navigation > Haiyang Xuebao > 2022 > 44(9): 38-54

Wu Youting，Yang Yang，Liang Xiangsan. Typical spatiotemporal patterns of the Kuroshio south of Japan and the Kuroshio extension using self-organizing maps and their causal relationship[J]. Haiyang Xuebao，2022, 44(9)：38–54 doi: 10.12284/hyxb2022069

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Typical spatiotemporal patterns of the Kuroshio south of Japan and the Kuroshio extension using self-organizing maps and their causal relationship

doi: 10.12284/hyxb2022069

Wu Youting^{1, 2
,},
Yang Yang^{3
,
,},
Liang Xiangsan^{4, 5}

1.
Key Laboratory of Marine Science and Numerical Modeling, First Institute of Oceanography, Ministry of Natural Resources, Qingdao 266061, China
2.
School of Marine Science, Nanjing University of Information Science and Technology, Nanjing 210044, China
3.
College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, China
4.
Department of Atmospheric and Oceanic Sciences, Fudan University, Shanghai 200438, China
5.
IRDR ICoE on Risk Interconnectivity and Governance on Weather/Climate Extremes Impact and Public Health, Fudan University, Shanghai 200438, China
6.
Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai 519000, China

Received Date: 2021-10-12
Rev Recd Date: 2022-01-25
Publish Date: 2022-08-29

Abstract

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.
- Kuroshio large meandering,
- Kuroshio extension,
- self-organizing map (SOM),
- causality analysis,
- information flow

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References(31)

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