Why the Southern Hemisphere ENSO responses lead ENSO

Daeho Jin, Ben P. Kirtman

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53 Scopus citations

Abstract

Abstract Analysis of observational estimates indicates that the El Niño-Southern Oscillation (ENSO) forced pattern in the extratropical Southern Hemisphere (SH), somewhat surprisingly, leads the peak phase of ENSO by one season. A Rossby wave source (RWS) analysis indicates that the tropical and extratropical RWS in the SH develops before the ENSO peak season and abruptly weakens thereafter. Further analysis shows that anomalous divergence/convergence and corresponding irrotational wind anomalies are sensitive to local seasonality. Numerical experiments in which the tropical Pacific is prescribed with perfectly periodic ENSO while all other oceans are simulated as a slab mixed layer model coupled to AGCM also show similar features. Additional numerical experiments in which ENSO forcing is shifted by 6 months (i.e., the ENSO peak in the southern winter season) indicate that the Northern Hemisphere atmosphere rather than the SH atmosphere precedes ENSO. This result supports the hypothesis that the ENSO forced pattern in the extratropics is strongly limited by local seasonality, rather than by the temporal phase of tropical remote forcing.

Original languageEnglish (US)
Article numberD23101
JournalJournal of Geophysical Research Atmospheres
Volume114
Issue number23
DOIs
StatePublished - Dec 2009

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ASJC Scopus subject areas

  • Geophysics
  • Forestry
  • Oceanography
  • Aquatic Science
  • Ecology
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Palaeontology

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