ENSO-driven interhemispheric Pacific mass transports

Shayne McGregor, J Paul Spence, Franziska U Schwarzkopf, Matthew Heathcote England, Agus Santoso, William S Kessler, Axel Timmermann, Claus Boning

Research output: Contribution to journalArticleResearchpeer-review

10 Citations (Scopus)

Abstract

Previous studies have shown that ENSO s anomalous equatorial winds, including the observed southward shift of zonal winds that occurs around the event peak, can be reconstructed with the first two Empirical Orthogonal Functions (EOFs) of equatorial region wind stresses. Using a high-resolution ocean general circulation model, we investigate the effect of these two EOFs on changes in warm water volume (WWV), interhemispheric mass transports, and Indonesian Throughflow (ITF). Wind stress anomalies associated with the first EOF produce changes in WWV that are dynamically consistent with the conceptual recharge oscillator paradigm. The ITF is found to heavily damp these WWV changes, reducing their variance by half. Wind stress anomalies associated with the second EOF, which depicts the southward wind shift, are responsible for WWV changes that are of comparable magnitude to those driven by the first mode. The southward wind shift is also responsible for the majority of the observed interhemispheric upper ocean mass exchanges. These winds transfer mass between the Northern and the Southern Hemisphere during El Nino events. Whilst water is transferred in the opposite direction during La Nina events, the magnitude of this exchange is roughly half of that seen during El Nino events. Thus, the discharging of WWV during El Nino events is meridionally asymmetric, while the WWV recharging during a La Nina event is largely symmetric. The inclusion of the southward wind shift is also shown to allow ENSO to exchange mass with much higher latitudes than that allowed by the first EOF alone. Key Points ENSO s southward wind shift is mostly responsible for interhemispheric exchanges ENSO phase asymmetry in the magnitude of the interhemispheric exchange El Nino discharge is meridionally asymmetric while La Nina recharge is symmetric (c) 2014. American Geophysical Union. All Rights Reserved.
Original languageEnglish
Pages (from-to)6221 - 6237
Number of pages17
JournalJournal of Geophysical Research: Oceans
Volume119
Issue number9
DOIs
Publication statusPublished - 2014
Externally publishedYes

Keywords

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

Cite this

McGregor, S., Spence, J. P., Schwarzkopf, F. U., England, M. H., Santoso, A., Kessler, W. S., ... Boning, C. (2014). ENSO-driven interhemispheric Pacific mass transports. Journal of Geophysical Research: Oceans, 119(9), 6221 - 6237. https://doi.org/10.1002/2014JC010286
McGregor, Shayne ; Spence, J Paul ; Schwarzkopf, Franziska U ; England, Matthew Heathcote ; Santoso, Agus ; Kessler, William S ; Timmermann, Axel ; Boning, Claus. / ENSO-driven interhemispheric Pacific mass transports. In: Journal of Geophysical Research: Oceans. 2014 ; Vol. 119, No. 9. pp. 6221 - 6237.
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McGregor, S, Spence, JP, Schwarzkopf, FU, England, MH, Santoso, A, Kessler, WS, Timmermann, A & Boning, C 2014, 'ENSO-driven interhemispheric Pacific mass transports', Journal of Geophysical Research: Oceans, vol. 119, no. 9, pp. 6221 - 6237. https://doi.org/10.1002/2014JC010286

ENSO-driven interhemispheric Pacific mass transports. / McGregor, Shayne; Spence, J Paul; Schwarzkopf, Franziska U; England, Matthew Heathcote; Santoso, Agus; Kessler, William S; Timmermann, Axel; Boning, Claus.

In: Journal of Geophysical Research: Oceans, Vol. 119, No. 9, 2014, p. 6221 - 6237.

Research output: Contribution to journalArticleResearchpeer-review

TY - JOUR

T1 - ENSO-driven interhemispheric Pacific mass transports

AU - McGregor, Shayne

AU - Spence, J Paul

AU - Schwarzkopf, Franziska U

AU - England, Matthew Heathcote

AU - Santoso, Agus

AU - Kessler, William S

AU - Timmermann, Axel

AU - Boning, Claus

PY - 2014

Y1 - 2014

N2 - Previous studies have shown that ENSO s anomalous equatorial winds, including the observed southward shift of zonal winds that occurs around the event peak, can be reconstructed with the first two Empirical Orthogonal Functions (EOFs) of equatorial region wind stresses. Using a high-resolution ocean general circulation model, we investigate the effect of these two EOFs on changes in warm water volume (WWV), interhemispheric mass transports, and Indonesian Throughflow (ITF). Wind stress anomalies associated with the first EOF produce changes in WWV that are dynamically consistent with the conceptual recharge oscillator paradigm. The ITF is found to heavily damp these WWV changes, reducing their variance by half. Wind stress anomalies associated with the second EOF, which depicts the southward wind shift, are responsible for WWV changes that are of comparable magnitude to those driven by the first mode. The southward wind shift is also responsible for the majority of the observed interhemispheric upper ocean mass exchanges. These winds transfer mass between the Northern and the Southern Hemisphere during El Nino events. Whilst water is transferred in the opposite direction during La Nina events, the magnitude of this exchange is roughly half of that seen during El Nino events. Thus, the discharging of WWV during El Nino events is meridionally asymmetric, while the WWV recharging during a La Nina event is largely symmetric. The inclusion of the southward wind shift is also shown to allow ENSO to exchange mass with much higher latitudes than that allowed by the first EOF alone. Key Points ENSO s southward wind shift is mostly responsible for interhemispheric exchanges ENSO phase asymmetry in the magnitude of the interhemispheric exchange El Nino discharge is meridionally asymmetric while La Nina recharge is symmetric (c) 2014. American Geophysical Union. All Rights Reserved.

AB - Previous studies have shown that ENSO s anomalous equatorial winds, including the observed southward shift of zonal winds that occurs around the event peak, can be reconstructed with the first two Empirical Orthogonal Functions (EOFs) of equatorial region wind stresses. Using a high-resolution ocean general circulation model, we investigate the effect of these two EOFs on changes in warm water volume (WWV), interhemispheric mass transports, and Indonesian Throughflow (ITF). Wind stress anomalies associated with the first EOF produce changes in WWV that are dynamically consistent with the conceptual recharge oscillator paradigm. The ITF is found to heavily damp these WWV changes, reducing their variance by half. Wind stress anomalies associated with the second EOF, which depicts the southward wind shift, are responsible for WWV changes that are of comparable magnitude to those driven by the first mode. The southward wind shift is also responsible for the majority of the observed interhemispheric upper ocean mass exchanges. These winds transfer mass between the Northern and the Southern Hemisphere during El Nino events. Whilst water is transferred in the opposite direction during La Nina events, the magnitude of this exchange is roughly half of that seen during El Nino events. Thus, the discharging of WWV during El Nino events is meridionally asymmetric, while the WWV recharging during a La Nina event is largely symmetric. The inclusion of the southward wind shift is also shown to allow ENSO to exchange mass with much higher latitudes than that allowed by the first EOF alone. Key Points ENSO s southward wind shift is mostly responsible for interhemispheric exchanges ENSO phase asymmetry in the magnitude of the interhemispheric exchange El Nino discharge is meridionally asymmetric while La Nina recharge is symmetric (c) 2014. American Geophysical Union. All Rights Reserved.

KW - El Nino-Southern Oscillation

KW - westerly wind

KW - El Nino

UR - http://onlinelibrary.wiley.com/doi/10.1002/2014JC010286/pdf

U2 - 10.1002/2014JC010286

DO - 10.1002/2014JC010286

M3 - Article

VL - 119

SP - 6221

EP - 6237

JO - Journal of Geophysical Research: Oceans

JF - Journal of Geophysical Research: Oceans

SN - 2169-9275

IS - 9

ER -

McGregor S, Spence JP, Schwarzkopf FU, England MH, Santoso A, Kessler WS et al. ENSO-driven interhemispheric Pacific mass transports. Journal of Geophysical Research: Oceans. 2014;119(9):6221 - 6237. https://doi.org/10.1002/2014JC010286