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

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12 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

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