Open AccessWhy the Southern Hemisphere ENSO responses lead ENSO
Author(s) -
Jin Daeho,
Kirtman Ben P.
Publication year - 2009
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2009jd012657
Subject(s) - climatology , extratropical cyclone , northern hemisphere , forcing (mathematics) , rossby wave , atmospheric sciences , southern hemisphere , atmosphere (unit) , environmental science , el niño southern oscillation , seasonality , madden–julian oscillation , geology , geography , meteorology , biology , convection , ecology
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.