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 Sciences University of São Paulo – Brazil VAMOS/MESA Meeting – Mexico City, Mexico 7 – 11 March, 2005

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

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

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

I = (X i - X i )/  i ENSO episodes and the South American Regional Precipitation 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 (Ambrizzi and Souza, 2003)

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

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

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

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

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 )

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

Climatological DJF Wind vector and intensity for the period hPa200 hPa (m/s)

Number of Jet occurrences = 17± , 88-89, Niña 82-83, 91-92, Niño Number of Jets

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

Weak El Niño DJF composite fields for Streamfunction anomalies during strong and weak ENSO events hPa (m 2 /s) Strong El Niño Strong La Niña Weak La Niña

Weak El Niño DJF composite fields for Streamfunction anomalies during strong and weak ENSO events hPa (m 2 /s) Strong El Niño Strong La Niña Weak La Niña

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

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

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

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

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

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

0°N, 120°W0°N, 160°W Wind Vector Anomaly at 850 hPa Baroclinic Model Experiments for the Heat Source Centered in the Equator - Streamfunction Anomaly

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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