Decadal amplitude modulation of two types of ENSO and its relationship with the mean state

Jung Choi, Soon Il An, Sang Wook Yeh

Research output: Contribution to journalArticle

46 Citations (Scopus)

Abstract

In this study, we classified two types of El Niño-Southern Oscillation (ENSO) events within the decadal ENSO amplitude modulation cycle using a long-term coupled general circulation model simulation. We defined two climate states-strong and weak ENSO amplitude periods-and separated the characteristics of ENSO that occurred in both periods. There are two major features in the characteristics of ENSO: the first is the asymmetric spatial structure between El Niño and La Niña events; the second is that the El Niño-La Niña asymmetry is reversed during strong and weak ENSO amplitude periods. El Niño events during strong (weak) ENSO amplitude periods resemble the Eastern Pacific (Central Pacific) El Niño in terms of the spatial distribution of sea surface temperature anomalies (SSTA) and physical characteristics based on heat budget analysis. The spatial pattern of the thermocline depth anomaly for strong (weak) El Niño is identical to that for weak (strong) La Niña, but for an opposite sign and slightly different amplitude. The accumulated residuals of these asymmetric anomalies dominated by an east-west contrast structure could feed into the tropical Pacific mean state. Moreover, the residual pattern associated with El Niño-La Niña asymmetry resembles the first principal component analysis (PCA) mode of tropical Pacific decadal variability, indicating that the accumulated residuals could generate the change in climate state. Thus, the intensified ENSO amplitude yields the warm residuals due to strong El Niño and weak La Niña over the eastern tropical Pacific. This linear relationship between ENSO and the mean state is strong during the mature phases of decadal oscillation, but it is weak during the transition phases. Furthermore, the second PCA mode of tropical Pacific decadal variability plays an important role in changing the phase of the first mode. Consequently, the feedback between ENSO and the mean state is positive feedback to amplify the first PCA mode, whereas the second PCA mode is a negative feedback to lead the phase change of the first PCA mode due to their lead-lag relationship. These features could be regarded as evidence that the decadal change in properties of ENSO could be generated by the nonlinear interaction between ENSO and the mean state on a decadal-to-interdecadal time scale.

Original languageEnglish
Pages (from-to)2631-2644
Number of pages14
JournalClimate Dynamics
Volume38
Issue number11-12
DOIs
Publication statusPublished - 2012 Jun 1

Fingerprint

Southern Oscillation
principal component analysis
asymmetry
anomaly
heat budget
climate
phase transition
thermocline
temperature anomaly
general circulation model
sea surface temperature
oscillation
spatial distribution
timescale

All Science Journal Classification (ASJC) codes

  • Atmospheric Science

Cite this

Choi, Jung ; An, Soon Il ; Yeh, Sang Wook. / Decadal amplitude modulation of two types of ENSO and its relationship with the mean state. In: Climate Dynamics. 2012 ; Vol. 38, No. 11-12. pp. 2631-2644.
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abstract = "In this study, we classified two types of El Ni{\~n}o-Southern Oscillation (ENSO) events within the decadal ENSO amplitude modulation cycle using a long-term coupled general circulation model simulation. We defined two climate states-strong and weak ENSO amplitude periods-and separated the characteristics of ENSO that occurred in both periods. There are two major features in the characteristics of ENSO: the first is the asymmetric spatial structure between El Ni{\~n}o and La Ni{\~n}a events; the second is that the El Ni{\~n}o-La Ni{\~n}a asymmetry is reversed during strong and weak ENSO amplitude periods. El Ni{\~n}o events during strong (weak) ENSO amplitude periods resemble the Eastern Pacific (Central Pacific) El Ni{\~n}o in terms of the spatial distribution of sea surface temperature anomalies (SSTA) and physical characteristics based on heat budget analysis. The spatial pattern of the thermocline depth anomaly for strong (weak) El Ni{\~n}o is identical to that for weak (strong) La Ni{\~n}a, but for an opposite sign and slightly different amplitude. The accumulated residuals of these asymmetric anomalies dominated by an east-west contrast structure could feed into the tropical Pacific mean state. Moreover, the residual pattern associated with El Ni{\~n}o-La Ni{\~n}a asymmetry resembles the first principal component analysis (PCA) mode of tropical Pacific decadal variability, indicating that the accumulated residuals could generate the change in climate state. Thus, the intensified ENSO amplitude yields the warm residuals due to strong El Ni{\~n}o and weak La Ni{\~n}a over the eastern tropical Pacific. This linear relationship between ENSO and the mean state is strong during the mature phases of decadal oscillation, but it is weak during the transition phases. Furthermore, the second PCA mode of tropical Pacific decadal variability plays an important role in changing the phase of the first mode. Consequently, the feedback between ENSO and the mean state is positive feedback to amplify the first PCA mode, whereas the second PCA mode is a negative feedback to lead the phase change of the first PCA mode due to their lead-lag relationship. These features could be regarded as evidence that the decadal change in properties of ENSO could be generated by the nonlinear interaction between ENSO and the mean state on a decadal-to-interdecadal time scale.",
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Decadal amplitude modulation of two types of ENSO and its relationship with the mean state. / Choi, Jung; An, Soon Il; Yeh, Sang Wook.

In: Climate Dynamics, Vol. 38, No. 11-12, 01.06.2012, p. 2631-2644.

Research output: Contribution to journalArticle

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AB - In this study, we classified two types of El Niño-Southern Oscillation (ENSO) events within the decadal ENSO amplitude modulation cycle using a long-term coupled general circulation model simulation. We defined two climate states-strong and weak ENSO amplitude periods-and separated the characteristics of ENSO that occurred in both periods. There are two major features in the characteristics of ENSO: the first is the asymmetric spatial structure between El Niño and La Niña events; the second is that the El Niño-La Niña asymmetry is reversed during strong and weak ENSO amplitude periods. El Niño events during strong (weak) ENSO amplitude periods resemble the Eastern Pacific (Central Pacific) El Niño in terms of the spatial distribution of sea surface temperature anomalies (SSTA) and physical characteristics based on heat budget analysis. The spatial pattern of the thermocline depth anomaly for strong (weak) El Niño is identical to that for weak (strong) La Niña, but for an opposite sign and slightly different amplitude. The accumulated residuals of these asymmetric anomalies dominated by an east-west contrast structure could feed into the tropical Pacific mean state. Moreover, the residual pattern associated with El Niño-La Niña asymmetry resembles the first principal component analysis (PCA) mode of tropical Pacific decadal variability, indicating that the accumulated residuals could generate the change in climate state. Thus, the intensified ENSO amplitude yields the warm residuals due to strong El Niño and weak La Niña over the eastern tropical Pacific. This linear relationship between ENSO and the mean state is strong during the mature phases of decadal oscillation, but it is weak during the transition phases. Furthermore, the second PCA mode of tropical Pacific decadal variability plays an important role in changing the phase of the first mode. Consequently, the feedback between ENSO and the mean state is positive feedback to amplify the first PCA mode, whereas the second PCA mode is a negative feedback to lead the phase change of the first PCA mode due to their lead-lag relationship. These features could be regarded as evidence that the decadal change in properties of ENSO could be generated by the nonlinear interaction between ENSO and the mean state on a decadal-to-interdecadal time scale.

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