Inter-El Ni

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Inter-El Niño variability and its impact on the
LLJ East of the Andes during Austral
Summer Tércio Ambrizzi and Gyrlene A. M. da
Silva Department of Atmospheric
SciencesUniversity of São Paulo Brazil
VAMOS/MESA Meeting Mexico City, Mexico7 11
March, 2005
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Schematic figures of the Atmosphere Circulation
during Canonical El Niño/La Niña eventos
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AVERAGE FOR 4 EL NIÑOS
Streamfunction Anomaly and Precipitation
Div Q and Omega Anomaly
(Ambrizzi and Magaña, 2005)
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ENSO episodes and the South American Regional
Precipitation
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El Niño episodes and the South American Regional
Precipitation during 1950-1990
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La Niña episodes and the South American Regional
Precipitation during 1950-1990
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SLC PACIFIC BOXES - DEC - MAY EL NIÑO
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SLC PACIFIC BOXES - DEC - MAY LA NIÑA
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• OBJETIVE
• To study the relationship between different
  intensities of ENSO events and the South America
  Low Level Jet East of the Andes during Austral
  Summer.
• METHODOLOGY
• Data composites and Baroclinic model experiments.
  
• DATA
• Monthly SST ( Wooddruf et al, 1987)
• OLR from 1975 2003 (Liebmann and Smith, 1996)
• Reanalysis (NCEP/NCAR) (Kalnay et al, 1996)
  From 1969-2003)

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ENSO Selected Events (CDC/NOAA)
El Niño 9 Weak, 2 Moderate, 3 Strong La Niña
4 Weak 3 Moderate 3 Strong Neutral 10 Summers
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DJF composite fields for SST anomalies during
strong and weak ENSO events (C)
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• FINAL COMMENTS
• SALLJ Frequency events higher during Strong and
  Weak El Niños and slightly below average during
  Strong and Weak La Niña events ? There is not a
  clear tendency during ENSO events
• SALLJ intensity and position during ENSO
• Strong El Niños ? higher amplitudes and
  displacement to the La Plata Basin region weak
  SACZ
• Weak El Niños and Strong and Weak La Niñas ?
  smaller amplitudes and displacement to the
  southeast of Brazil strong SACZ (Liebmann et
  al, 2004, JC)
• Source of moisture in the corridor along the
  eastern slope of the Andes during El Niños ?
  trade winds During La Niñas it seems that the
  east Pacific ocean may play some role
• Transients are important to modulate the position
  of the SALLJ
• Simple numerical experiments suggest that the
  tropical forcing plays an important part on the
  intensification of the jet but it is dependent of
  the synoptic activities to better positioning of
  it.

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THANKS TO JOSS/UCAR FOR THE TRAVEL SUPPORT TO
THIS MEETING
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