Combination mode dynamics of the anomalous northwest Pacific anticyclone

Malte F Stuecker, Fei-Fei Jin, Axel Timmermann, Shayne McGregor

Research output: Contribution to journalArticleResearchpeer-review

71 Citations (Scopus)

Abstract

Nonlinear interactions between ENSO and the western Pacific warm pool annual cycle generate an atmospheric combination mode (C-mode) of wind variability. The authors demonstrate that C-mode dynamics are responsible for the development of an anomalous low-level northwest Pacific anticyclone (NWP-AC) during El Nino events. The NWP-AC is embedded in a large-scale meridionally antisymmetric Indo-Pacific atmospheric circulation response and has been shown to exhibit large impacts on precipitation in Asia. In contrast to previous studies, the authors find the role of air-sea coupling in the Indian Ocean and northwestern Pacific only of secondary importance for the NWP-AC genesis.Moreover, the NWP-AC is clearly marked in the frequency domain with near-annual combination tones, which have been overlooked in previous Indo-Pacific climate studies. Furthermore, the authors hypothesize a positive feedback loop involving the anomalous low-level NWP-AC through El Nino and C-mode interactions: the development of the NWP-AC as a result of the C-mode acts to rapidly terminate El Nino events. The subsequent phase shift from retreating El Nino conditions toward a developing La Nina phase terminates the low-level cyclonic circulation response in the central Pacific and thus indirectly enhances the NWP-AC and allows it to persist until boreal summer. Anomalous local circulation features in the Indo-Pacific (e.g., the NWP AC) can be considered a superposition of the quasi-symmetric linear ENSO response and the meridionally antisymmetric annual cycle modulated ENSO response (C-mode). The authors emphasize that it is not adequate to assess ENSO impacts by considering only interannual time scales. C-mode dynamics are an essential (extended) part of ENSO and result in a wide range of deterministic high-frequency variability. (c) 2015 American Meteorological Society.
Original languageEnglish
Pages (from-to)1093 - 1111
Number of pages19
JournalJournal of Climate
Volume28
Issue number3
DOIs
Publication statusPublished - 2015
Externally publishedYes

Keywords

  • El Nino-Southern Oscillation
  • westerly wind
  • El Nino

Cite this

Stuecker, Malte F ; Jin, Fei-Fei ; Timmermann, Axel ; McGregor, Shayne. / Combination mode dynamics of the anomalous northwest Pacific anticyclone. In: Journal of Climate. 2015 ; Vol. 28, No. 3. pp. 1093 - 1111.
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Combination mode dynamics of the anomalous northwest Pacific anticyclone. / Stuecker, Malte F; Jin, Fei-Fei; Timmermann, Axel; McGregor, Shayne.

In: Journal of Climate, Vol. 28, No. 3, 2015, p. 1093 - 1111.

Research output: Contribution to journalArticleResearchpeer-review

TY - JOUR

T1 - Combination mode dynamics of the anomalous northwest Pacific anticyclone

AU - Stuecker, Malte F

AU - Jin, Fei-Fei

AU - Timmermann, Axel

AU - McGregor, Shayne

PY - 2015

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N2 - Nonlinear interactions between ENSO and the western Pacific warm pool annual cycle generate an atmospheric combination mode (C-mode) of wind variability. The authors demonstrate that C-mode dynamics are responsible for the development of an anomalous low-level northwest Pacific anticyclone (NWP-AC) during El Nino events. The NWP-AC is embedded in a large-scale meridionally antisymmetric Indo-Pacific atmospheric circulation response and has been shown to exhibit large impacts on precipitation in Asia. In contrast to previous studies, the authors find the role of air-sea coupling in the Indian Ocean and northwestern Pacific only of secondary importance for the NWP-AC genesis.Moreover, the NWP-AC is clearly marked in the frequency domain with near-annual combination tones, which have been overlooked in previous Indo-Pacific climate studies. Furthermore, the authors hypothesize a positive feedback loop involving the anomalous low-level NWP-AC through El Nino and C-mode interactions: the development of the NWP-AC as a result of the C-mode acts to rapidly terminate El Nino events. The subsequent phase shift from retreating El Nino conditions toward a developing La Nina phase terminates the low-level cyclonic circulation response in the central Pacific and thus indirectly enhances the NWP-AC and allows it to persist until boreal summer. Anomalous local circulation features in the Indo-Pacific (e.g., the NWP AC) can be considered a superposition of the quasi-symmetric linear ENSO response and the meridionally antisymmetric annual cycle modulated ENSO response (C-mode). The authors emphasize that it is not adequate to assess ENSO impacts by considering only interannual time scales. C-mode dynamics are an essential (extended) part of ENSO and result in a wide range of deterministic high-frequency variability. (c) 2015 American Meteorological Society.

AB - Nonlinear interactions between ENSO and the western Pacific warm pool annual cycle generate an atmospheric combination mode (C-mode) of wind variability. The authors demonstrate that C-mode dynamics are responsible for the development of an anomalous low-level northwest Pacific anticyclone (NWP-AC) during El Nino events. The NWP-AC is embedded in a large-scale meridionally antisymmetric Indo-Pacific atmospheric circulation response and has been shown to exhibit large impacts on precipitation in Asia. In contrast to previous studies, the authors find the role of air-sea coupling in the Indian Ocean and northwestern Pacific only of secondary importance for the NWP-AC genesis.Moreover, the NWP-AC is clearly marked in the frequency domain with near-annual combination tones, which have been overlooked in previous Indo-Pacific climate studies. Furthermore, the authors hypothesize a positive feedback loop involving the anomalous low-level NWP-AC through El Nino and C-mode interactions: the development of the NWP-AC as a result of the C-mode acts to rapidly terminate El Nino events. The subsequent phase shift from retreating El Nino conditions toward a developing La Nina phase terminates the low-level cyclonic circulation response in the central Pacific and thus indirectly enhances the NWP-AC and allows it to persist until boreal summer. Anomalous local circulation features in the Indo-Pacific (e.g., the NWP AC) can be considered a superposition of the quasi-symmetric linear ENSO response and the meridionally antisymmetric annual cycle modulated ENSO response (C-mode). The authors emphasize that it is not adequate to assess ENSO impacts by considering only interannual time scales. C-mode dynamics are an essential (extended) part of ENSO and result in a wide range of deterministic high-frequency variability. (c) 2015 American Meteorological Society.

KW - El Nino-Southern Oscillation

KW - westerly wind

KW - El Nino

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U2 - 10.1175/JCLI-D-14-00225.1

DO - 10.1175/JCLI-D-14-00225.1

M3 - Article

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EP - 1111

JO - Journal of Climate

JF - Journal of Climate

SN - 0894-8755

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