LINKAGE BETWEEN INDIAN OCEAN DIPOLE AND TWO TYPES OF El NIÑO AND ITS POSSIBLE MECHANISMS

DONG Di; HE Jin-hai; LI Jian-ping

doi:10.16555/j.1006-8775.2016.02.007

Abstract:

After compositing three representative ENSO indices, El Niño events have been divided into an eastern pattern (EP) and a central pattern (CP). By using EOF, correlation and composite analysis, the relationship and possible mechanisms between Indian Ocean Dipole (IOD) and two types of El Niño were investigated. IOD events, originating from Indo-Pacific scale air-sea interaction, are composed of two modes, which are associated with EP and CP El Niño respectively. The IOD mode related to EP El Niño events (named as IOD1) is strongest at the depth of 50 to 150 m along the equatorial Indian Ocean. Besides, it shows a quasi-symmetric distribution, stronger in the south of the Equator. The IOD mode associated with CP El Niño (named as IOD2) has strongest signal in tropical southern Indian Ocean surface. In terms of mechanisms, before EP El Niño peaks, anomalous Walker circulation produces strong anomalous easterlies in equatorial Indian Ocean, resulting in upwelling in the east, decreasing sea temperature there; a couple of anomalous anticyclones (stronger in the south) form off the Equator where warm water accumulates, and thus the IOD1 occurs. When CP El Niño develops, anomalous Walker circulation is weaker and shifts its center to the west, therefore anomalous easterlies in equatorial Indian Ocean is less strong. Besides, the anticyclone south of Sumatra strengthens, and the southerlies east of it bring cold water from higher latitudes and northerlies west of it bring warm water from lower latitudes to the 15° to 25°S zone. Meanwhile, there exists strong divergence in the east and convergence in the west part of tropical southern Indian Ocean, making sea temperature fall and rise separately. Therefore, IOD2 lies farther south.

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DONG Di, HE Jin-hai, LI Jian-ping. LINKAGE BETWEEN INDIAN OCEAN DIPOLE AND TWO TYPES OF El NIÑO AND ITS POSSIBLE MECHANISMS [J]. Journal of Tropical Meteorology, 2016, 22(2): 172-181, https://doi.org/10.16555/j.1006-8775.2016.02.007

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LINKAGE BETWEEN INDIAN OCEAN DIPOLE AND TWO TYPES OF El NIÑO AND ITS POSSIBLE MECHANISMS

State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029 China College of Earth Science, University of Chinese Academy of Sciences,

Rev Recd Date: 2015-12-02

Abstract: After compositing three representative ENSO indices, El Niño events have been divided into an eastern pattern (EP) and a central pattern (CP). By using EOF, correlation and composite analysis, the relationship and possible mechanisms between Indian Ocean Dipole (IOD) and two types of El Niño were investigated. IOD events, originating from Indo-Pacific scale air-sea interaction, are composed of two modes, which are associated with EP and CP El Niño respectively. The IOD mode related to EP El Niño events (named as IOD1) is strongest at the depth of 50 to 150 m along the equatorial Indian Ocean. Besides, it shows a quasi-symmetric distribution, stronger in the south of the Equator. The IOD mode associated with CP El Niño (named as IOD2) has strongest signal in tropical southern Indian Ocean surface. In terms of mechanisms, before EP El Niño peaks, anomalous Walker circulation produces strong anomalous easterlies in equatorial Indian Ocean, resulting in upwelling in the east, decreasing sea temperature there; a couple of anomalous anticyclones (stronger in the south) form off the Equator where warm water accumulates, and thus the IOD1 occurs. When CP El Niño develops, anomalous Walker circulation is weaker and shifts its center to the west, therefore anomalous easterlies in equatorial Indian Ocean is less strong. Besides, the anticyclone south of Sumatra strengthens, and the southerlies east of it bring cold water from higher latitudes and northerlies west of it bring warm water from lower latitudes to the 15° to 25°S zone. Meanwhile, there exists strong divergence in the east and convergence in the west part of tropical southern Indian Ocean, making sea temperature fall and rise separately. Therefore, IOD2 lies farther south.

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LINKAGE BETWEEN INDIAN OCEAN DIPOLE AND TWO TYPES OF El NIÑO AND ITS POSSIBLE MECHANISMS

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