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Inter-El Niño variability and its impact on the LLJ East of the Andes during Austral Summer

This study aims to investigate the relationship between different intensities of El Niño events and the South America Low-Level Jet (LLJ) east of the Andes during the austral summer. Data composites and baroclinic model experiments were used to analyze the SST anomalies, streamfunction anomalies, and other atmospheric variables. The results show that the LLJ frequency and intensity are influenced by El Niño events, with strong El Niños causing higher amplitudes and displacement to the La Plata Basin region. We also found that transients and synoptic activities play a role in modulating the position of the LLJ. Visit our website for more information.

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Inter-El Niño variability and its impact on the LLJ East of the Andes during Austral Summer

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  1. Inter-El Niño variability and its impact on the LLJ East of the Andes during Austral Summer Tércio Ambrizzi and Gyrlene A. M. da SilvaDepartment of Atmospheric SciencesUniversity of São Paulo – Brazil VAMOS/MESA Meeting – Mexico City, Mexico7 – 11 March, 2005

  2. Conceptual model of the SALLJ physical environment during the wet season (Marengo et al. 2004 - JC)

  3. EL NIÑO LA NIÑA Schematic figures of the Atmosphere Circulation during Canonical El Niño/La Niña eventos

  4. AVERAGE FOR 4 EL NIÑOS Streamfunction Anomaly and Precipitation Div Q and Omega Anomaly (Ambrizzi and Magaña, 2005)

  5. Seasonal Standardized index for the austral summer (DJF) and autumn (MAM) were calculated for the precipitation over key-areas of South America and the SSTa over the Niño 1.2, 3, 3.4 and 4 I = (Xi - Xi)/i (Ambrizzi and Souza, 2003) ENSO episodes and the South American Regional Precipitation

  6. Niños SSTa E Amazon NE Brazil SACZ SE South America Altiplano Ecuador Peru El Niño episodes and the South American Regional Precipitation during 1950-1990

  7. Niñas SSTa E Amazon NE Brazil SACZ SE South America Altiplano Ecuador Peru La Niña episodes and the South American Regional Precipitation during 1950-1990

  8. C B SVD E G (Coelho, Uvo and Ambrizzi, 2002 – TAC) SLC – PACIFIC BOXES - DEC - MAY – EL NIÑO

  9. E B SVD F G (Coelho, Uvo and Ambrizzi, 2002 – TAC) SLC – PACIFIC BOXES - DEC - MAY – LA NIÑA

  10. 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)

  11. ENSO Selected Events (CDC/NOAA) El Niño – 9 Weak, 2 Moderate, 3 Strong La Niña – 4 Weak; 3 Moderate; 3 Strong Neutral – 10 Summers

  12. Climatological DJF Wind vector and intensity for the period 1969 - 2003 850 hPa 200 hPa (m/s)

  13. Number of Jets 73-74, 88-89, 00-01 Niña 82-83, 91-92, 98-99 Niño Number of Jet occurrences = 17± 8

  14. Strong El Niño Weak El Niño Strong La Niña Weak La Niña DJF composite fields for SST anomalies during strong and weak ENSO events (°C)

  15. DJF composite fields for Streamfunction anomalies during strong and weak ENSO events - 200 hPa (m2/s) Strong El Niño Weak El Niño Strong La Niña Weak La Niña

  16. DJF composite fields for Streamfunction anomalies during strong and weak ENSO events - 850 hPa (m2/s) Strong El Niño Weak El Niño Strong La Niña Weak La Niña

  17. DJF Composite Fields of Water Vapor Flux and Divergence Anomaly (g/ms) Weak El Niño Strong El Niño Weak La Niña Strong La Niña

  18. SLP Anomalies and Wind Vector at 850 hPa for Strong El Niño Events Day -1 Day -2 Day +1 Day 0

  19. SLP Anomalies and Wind Vector at 850 hPa for Weak El Niño Events Day -1 Day -2 Day +1 Day 0

  20. SLP Anomalies and Wind Vector at 850 hPa for Strong La Niña Events Day -1 Day -2 Day +1 Day 0

  21. SLP Anomalies and Wind Vector at 850 hPa for Weak La Niña Events Day -1 Day -2 Day +1 Day 0

  22. Conceptual Diagram of the SALLJ average position during ENSO extreme events Weak El Niño Strong El Niño Weak La Niña Strong La Niña

  23. Baroclinic Model Experiments for the Heat Source Centered in the Equator - Streamfunction Anomaly 0°N, 120°W 0°N, 160°W Wind Vector Anomaly at 850 hPa

  24. 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.

  25. Climate Studies Group THANKS TO JOSS/UCAR FOR THE TRAVEL SUPPORT TO THIS MEETING Visit the website www.grec.iag.usp.br

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