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ENSO and SAM influence on the generation of long episodes of Rossby Wave Packets during Southern Hemisphere Summer
  • Iago Perez,
  • Marcelo Barreiro,
  • Cristina Masoller
Iago Perez
Universidad de la República

Corresponding Author:iagopf93@gmail.com

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Marcelo Barreiro
Facultad de Ciencias, Universidad de la Republica, Uruguay
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Cristina Masoller
Universitat Politecnica de Catalunya
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This study aims at understanding the impact of low-frequency climate modes on Rossby Wave Packets (RWPs) during the southern hemisphere summer. In particular, we focus on long-lived RWPs (lifespan above 8 days) and determine how El Niño-Southern Oscillation (ENSO) and Southern Annular Mode (SAM) modulate their frequency of occurrence plus the main areas of detection and dissipation. We find that the occurrence of long lived RWPs is maximum during El Niño years and negative SAM events. Years with largest numbers of long-lived RWPs are characterized by a zonally symmetric and narrow upper level jet that is shifted northward from its climatological position. Conversely, when the jet is shifted southward, as during positive SAM phases, particularly in the southwestern Pacific basin, the number of long-lived RWPs detected diminishes. El Niño sets atmospheric conditions that support the formation of long lived RWPs whereas La Niña years presents high interannual variability in the frequency of occurrence. Moreover, during El Niño events the main formation area is between 61-120ºE and its main dissipation area between 300-359ºE. During La Niña events, the main formation area moves to 241-300ºE and no main dissipation area is identified. During positive SAM two main formation areas appear at 61-120ºE and 241-300ºE and two main dissipation areas between 121-180º and 301-359º, whereas in negative SAM only one formation area at 241-300º is detected and no main dissipation area is found.
27 Dec 2021Published in Journal of Geophysical Research: Atmospheres volume 126 issue 24. 10.1029/2021JD035467