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Interannual variability and mechanism of ocean stratification over the Kuroshio Extension region in the warm season

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Abstract

The Kuroshio Extension (KE) area is thought to be a “hotspot” of climate and biology in the North Pacific. The variations of density stratification of seasonal thermocline over this area in the warm season can modulate the oceanic response and feedback to atmospheric and biogeochemical processes in winter. As such, we investigate the interannual variability and mechanism of the stratification using the potential energy anomaly (PEA) analysis based on observations and high-resolution ocean reanalysis data. It is found that the stratification has a significant interannual variability that is associated with the KE bimodality: the stratification is weak when the KE takes a stable state, while it is relatively strong when the KE is in an unstable state. The PEA budget analysis shows that PEA advection processes by flow velocity have remarkable differences under the KE stable and unstable states and, in turn, determine the interannual variability of the stratification over the KE region in the warm season. Furthermore, the advection process is mainly caused by the average flow field, while the eddy-induced advection is almost negligible.

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Data availability

AVISO data is available from https://www.aviso.altimetry.fr. FORA data is from http://search.diasjp.net/en/dataset/FORA_WNP30_JAMSTEC_MRI. EN4 data can be obtained from https://www.metoffice.gov.uk/hadobs/en4/. The atmospheric forcing data including the sensible heat flux, latent heat flux, the longwave radiation flux, the shortwave radiation flux, evaporation, and precipitation is available from JRA-55 (https://jra.kishou.go.jp/JRA-55).

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Acknowledgements

We thank two anonymous reviewers for their constructive suggestions and comments, which help us to significantly improve the study.

Funding

This study was supported by the National Natural Science Foundation of China (42076017), the Strategic Priority Research Program of Chinese Academy of Sciences (XDA20060502), and the Fundamental Research Funds for the Central Universities (B200201011).

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Authors and Affiliations

  1. Key Laboratory of Marine Hazards Forecasting, Ministry of Natural Resources, Hohai University, Nanjing, China

    Qiang Wang

  2. College of Oceanography, Hohai University, Nanjing, China

    Qiang Wang & Xiaohan Li

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  1. Qiang Wang
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  2. Xiaohan Li
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Contributions

QW conceived the study. QW and XL collected and analyzed the data. QW wrote the initial manuscript text. Both authors discussed the results and commented on the manuscript.

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Correspondence to Qiang Wang.

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Wang, Q., Li, X. Interannual variability and mechanism of ocean stratification over the Kuroshio Extension region in the warm season. Clim Dyn 61, 3481–3497 (2023). https://doi.org/10.1007/s00382-023-06753-3

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