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IOD-Driven Quasi-Biennial Variability Influence on Indian Ocean Equatorial Undercurrent.

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Title: IOD-Driven Quasi-Biennial Variability Influence on Indian Ocean Equatorial Undercurrent.
Authors: Huang, Ke1,2,3 (AUTHOR) kehuang@scsio.ac.cn, Wang, Dongxiao4 (AUTHOR) dxwang@mail.sysu.edu.cn, Zhu, Yingli5 (AUTHOR), Zhou, Wei1 (AUTHOR), Yao, Jinglong1 (AUTHOR), Peng, Bo6 (AUTHOR)
Source: Journal of Climate. Dec2025, Vol. 38 Issue 23, p6907-6927. 21p.
Subjects: Quasi-biennial oscillation (Meteorology), Hilbert-Huang transform, Fluctuations (Physics), Ocean dynamics, Ocean, Ocean currents, Climate change
Geographic Terms: Indian Ocean
Abstract: Inherent quasi-biennial (QB) variability (with a period of 1.5–2 years) of the Indian Ocean dipole (IOD) significantly influences the interannual variability of the Indian Ocean Equatorial Undercurrent (IO-EUC), yet it has received limited attention until now. This study investigates the QB variability of the IO-EUC, focusing on its phase transitions and dynamical connections to the IOD, using long-term ocean reanalysis and linear ocean model outputs with various statistical methods. Two leading empirical orthogonal function (EOF) modes of anomalous subsurface zonal currents capture the dominant QB variability of the IO-EUC. A coherent temporal lead–lag relationship of 4–5 months between the principal components of these leading modes indicates a typical life cycle characterized by a basinwide, same-sign displacement along the equator during equilibrium phases, and an east–west tilting subsurface mode during disequilibrium phases. Consistent with the inherent-oscillation framework of the IOD, the switch between positive and negative IOD stages, along with the propagations and reflections of wind-forced and boundary-reflected equatorial waves, contributes to the QB component and phase transition mechanisms of the IO-EUC. Importantly, higher-order baroclinic mode Rossby waves with relatively slower phase speeds are found to play a crucial role in shaping the life cycle and phase transitions of IO-EUC under the inherent IOD oscillation. These findings enhance our understanding on the new scenario of the Indian Ocean current system in maintaining and redistributing tracers throughout the climate system. Significance Statement: The Indian Ocean Equatorial Undercurrent (IO-EUC) is a key oceanic jet that transports heat and salt across the equator, influencing regional and global climate. This study shows that the IO-EUC follows a natural quasi-biennial (∼2-yr) variability closely linked to the Indian Ocean dipole. Using observational data and model outputs spanning the past four decades, we find that shifts in winds and oscillation within the equatorial ocean drive changes in the life cycle and phase transitions of the IO-EUC. The results highlight how ocean–atmosphere interactions induce the oceanic internal oscillations that slowly propagate across the basin in regulating IO-EUC variability. Understanding these natural processes improves our ability to predict Indian Ocean behaviors and their impacts on climate systems. [ABSTRACT FROM AUTHOR]
Copyright of Journal of Climate is the property of American Meteorological Society and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: IOD-Driven Quasi-Biennial Variability Influence on Indian Ocean Equatorial Undercurrent.
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  Data: <searchLink fieldCode="AR" term="%22Huang%2C+Ke%22">Huang, Ke</searchLink><relatesTo>1,2,3</relatesTo> (AUTHOR)<i> kehuang@scsio.ac.cn</i><br /><searchLink fieldCode="AR" term="%22Wang%2C+Dongxiao%22">Wang, Dongxiao</searchLink><relatesTo>4</relatesTo> (AUTHOR)<i> dxwang@mail.sysu.edu.cn</i><br /><searchLink fieldCode="AR" term="%22Zhu%2C+Yingli%22">Zhu, Yingli</searchLink><relatesTo>5</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Zhou%2C+Wei%22">Zhou, Wei</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Yao%2C+Jinglong%22">Yao, Jinglong</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Peng%2C+Bo%22">Peng, Bo</searchLink><relatesTo>6</relatesTo> (AUTHOR)
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  Data: <searchLink fieldCode="JN" term="%22Journal+of+Climate%22">Journal of Climate</searchLink>. Dec2025, Vol. 38 Issue 23, p6907-6927. 21p.
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  Data: <searchLink fieldCode="DE" term="%22Quasi-biennial+oscillation+%28Meteorology%29%22">Quasi-biennial oscillation (Meteorology)</searchLink><br /><searchLink fieldCode="DE" term="%22Hilbert-Huang+transform%22">Hilbert-Huang transform</searchLink><br /><searchLink fieldCode="DE" term="%22Fluctuations+%28Physics%29%22">Fluctuations (Physics)</searchLink><br /><searchLink fieldCode="DE" term="%22Ocean+dynamics%22">Ocean dynamics</searchLink><br /><searchLink fieldCode="DE" term="%22Ocean%22">Ocean</searchLink><br /><searchLink fieldCode="DE" term="%22Ocean+currents%22">Ocean currents</searchLink><br /><searchLink fieldCode="DE" term="%22Climate+change%22">Climate change</searchLink>
– Name: SubjectGeographic
  Label: Geographic Terms
  Group: Su
  Data: <searchLink fieldCode="DE" term="%22Indian+Ocean%22">Indian Ocean</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: Inherent quasi-biennial (QB) variability (with a period of 1.5–2 years) of the Indian Ocean dipole (IOD) significantly influences the interannual variability of the Indian Ocean Equatorial Undercurrent (IO-EUC), yet it has received limited attention until now. This study investigates the QB variability of the IO-EUC, focusing on its phase transitions and dynamical connections to the IOD, using long-term ocean reanalysis and linear ocean model outputs with various statistical methods. Two leading empirical orthogonal function (EOF) modes of anomalous subsurface zonal currents capture the dominant QB variability of the IO-EUC. A coherent temporal lead–lag relationship of 4–5 months between the principal components of these leading modes indicates a typical life cycle characterized by a basinwide, same-sign displacement along the equator during equilibrium phases, and an east–west tilting subsurface mode during disequilibrium phases. Consistent with the inherent-oscillation framework of the IOD, the switch between positive and negative IOD stages, along with the propagations and reflections of wind-forced and boundary-reflected equatorial waves, contributes to the QB component and phase transition mechanisms of the IO-EUC. Importantly, higher-order baroclinic mode Rossby waves with relatively slower phase speeds are found to play a crucial role in shaping the life cycle and phase transitions of IO-EUC under the inherent IOD oscillation. These findings enhance our understanding on the new scenario of the Indian Ocean current system in maintaining and redistributing tracers throughout the climate system. Significance Statement: The Indian Ocean Equatorial Undercurrent (IO-EUC) is a key oceanic jet that transports heat and salt across the equator, influencing regional and global climate. This study shows that the IO-EUC follows a natural quasi-biennial (∼2-yr) variability closely linked to the Indian Ocean dipole. Using observational data and model outputs spanning the past four decades, we find that shifts in winds and oscillation within the equatorial ocean drive changes in the life cycle and phase transitions of the IO-EUC. The results highlight how ocean–atmosphere interactions induce the oceanic internal oscillations that slowly propagate across the basin in regulating IO-EUC variability. Understanding these natural processes improves our ability to predict Indian Ocean behaviors and their impacts on climate systems. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Journal of Climate is the property of American Meteorological Society and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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RecordInfo BibRecord:
  BibEntity:
    Identifiers:
      – Type: doi
        Value: 10.1175/JCLI-D-25-0015.1
    Languages:
      – Code: eng
        Text: English
    PhysicalDescription:
      Pagination:
        PageCount: 21
        StartPage: 6907
    Subjects:
      – SubjectFull: Quasi-biennial oscillation (Meteorology)
        Type: general
      – SubjectFull: Hilbert-Huang transform
        Type: general
      – SubjectFull: Fluctuations (Physics)
        Type: general
      – SubjectFull: Ocean dynamics
        Type: general
      – SubjectFull: Ocean
        Type: general
      – SubjectFull: Ocean currents
        Type: general
      – SubjectFull: Climate change
        Type: general
      – SubjectFull: Indian Ocean
        Type: general
    Titles:
      – TitleFull: IOD-Driven Quasi-Biennial Variability Influence on Indian Ocean Equatorial Undercurrent.
        Type: main
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          Name:
            NameFull: Huang, Ke
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            NameFull: Wang, Dongxiao
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            NameFull: Zhu, Yingli
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            NameFull: Zhou, Wei
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            NameFull: Yao, Jinglong
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            – D: 01
              M: 12
              Text: Dec2025
              Type: published
              Y: 2025
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