Inter-El Niño variability and its impact on the South American low-level jet east of the Andes during austral summer − two case studies

Silva, G. A. M.; Ambrizzi, Tércio

doi:10.5194/adgeo-6-283-2006

Cited by 41 publications

(46 citation statements)

References 18 publications

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“…Marengo et al (2004), Lau andZhou (2003) andNieto Ferreira et al (2003) have also indicated that the 1997/98 EN had more frequent and strong SALLJ episodes when compared to the 1999/2000 La Niña (LN) event. Silva and Ambrizzi (2006) verified that during the event of 1997/98 a low-level anomalous anticyclonic circulation over the central part of Brazil enhanced the wind in the core of the SALLJ and displaced the jet to the Northern Argentina and South of Brazil. On the other hand, during the weak EN 2002/03 the SALLJ was less intense and displaced towards the southeast of Brazil.…”

Section: Introductionmentioning

confidence: 71%

“…The methodology of previous studies Marengo et al, 2002Marengo et al, , 2004Silva and Ambrizzi, 2006) was applied to wind data (u, v) to select the SALLJ episodes according to each ENSO event. It was assumed that the region of Santa Cruz in Bolivia (17.75 • S; 63.06 • W) is where the core of the jet is usually located and only the northerly wind was selected.…”

Section: Methodsmentioning

confidence: 99%

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Observational evidences on the modulation of the South American Low Level Jet east of the Andes according the ENSO variability

Silva¹,

Ambrizzi²,

Marengo

2009

Ann. Geophys.

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Abstract. The differences on the phase and wavelength of the quasi-stationary waves over the South America generated by El Niño (EN) and La Niña (LN) events seem to affect the daily evolution of the South American Low Level Jet east of the Andes (SALLJ). For the austral summer period of 1977-2004 the SALLJ episodes detected according to Bonner criterion 1 show normal to above-normal frequency in EN years, and in LN years the episodes show normal to below-normal frequency.During EN and LN years the SALLJ episodes were associated with positive rainfall anomalies over the La Plata Basin, but more intense during LN years. During EN years the increase in the SALLJ cases were associated to intensification of the Subtropical Jet (SJ) around 30 • S and positive Sea Level Pressure (SLP) anomalies over the western equatorial Atlantic and tropical South America, particularly over central Brazil. This favored the intensification of the northeasterly trade winds over the northern continent and it channeled by the Andes mountain to the La Plata Basin region where negative SLP are found. The SALLJ cases identified during the LN events were weaker and less frequent when compared to those for EN years. In this case the SJ was weaker than in EN years and the negative SLP anomalies over the tropical continent contributed to the inversion of the northeasterly trade winds. Also a southerly flow anomaly was generated by the geostrophic balance due to the anomalous blocking over southeast Pacific and the intense cyclonic transient over the southern tip of South America. As result the warm tropical air brought by the SALLJ encounters the cold extratropical air from the southerly winds over the La Correspondence to: G. A. M. Silva (gyrlene@model.iag.usp.br) Plata basin. This configuration can increase the conditional instability over the La Plata basin and may explain the more intense positive rainfall anomalies in SALLJ cases during LN years than in EN years.

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Section: Introductionmentioning

confidence: 71%

Section: Methodsmentioning

confidence: 99%

Observational evidences on the modulation of the South American Low Level Jet east of the Andes according the ENSO variability

Silva¹,

Ambrizzi²,

Marengo

2009

Ann. Geophys.

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“…10. and mesoscale environments over South America, which in turn can influence convective activity and precipitation patterns across the tropical and subtropical regions (e.g., Curtis 2008;Silva and Ambrizzi 2006;Nieto Ferreira et al 2003;Lau and Zhou 2003;Grimm et al 2000Grimm et al , 1998Ropelewski andHalpert 1989, 1987;Velasco and Frisch 1987). 7, but by warm season.…”

Section: El Nin˜o-southern Oscillationmentioning

confidence: 99%

The Contribution of Mesoscale Convective Complexes to Rainfall across Subtropical South America

2009

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This study uses a database consisting of 330 austral warm-season (October-May) mesoscale convective complexes (MCCs) during 1998-2007 to determine the contribution of MCCs to rainfall across subtropical South America (SSA). A unique precipitation analysis is conducted using Tropical Rainfall Measuring Mission (TRMM) 3B42 version 6 data. The average MCC produces 15.7 mm of rainfall across 381 000 km 2 , with a volume of 7.0 km 3 . MCCs in SSA have the largest precipitation areas compared to North American and African systems. MCCs accounted for 15%-21% of the total rainfall across portions of northern Argentina and Paraguay during 1998-2007. However, MCCs account for larger fractions of the total precipitation when analyzed on monthly and warm-season time scales. Widespread MCC rainfall contributions of 11%-20% were observed in all months. MCCs accounted for 20%-30% of the total rainfall between November and February, and 30%-50% in December, primarily across northern Argentina and Paraguay. MCCs also produced 25%-66% of the total rainfall across portions of west-central Argentina. Similar MCC rainfall contributions were observed during warm seasons. An MCC impact factor (MIF) was developed to determine the overall impact of MCC rainfall on warm-season precipitation anomalies. Results show that the greatest impacts on precipitation anomalies from MCC rainfall were located near the center of the La Plata basin. This study demonstrates that MCCs in SSA produce widespread precipitation that contributes substantially to the total rainfall across the region.

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“…[5] Motivated by the observational study of Silva and Ambrizzi [2006] and with no previous model studies with such an experimental design available, we investigate here the impact of the 1997 (EN97) and 2002 (EN02) El Niño events on the climate over South America, using not only observations but also ACGM ensemble experiments. We focus our analyses on the South American monsoon season, i.e., DJF.…”

Section: Introductionmentioning

confidence: 99%

South American rainfall impacts associated with inter‐El Niño variations

Hill¹,

Taschetto²,

England³

2009

Geophysical Research Letters

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The impacts of inter‐El Niño events on South American circulation during austral summer are investigated using observations and an atmospheric general circulation model (AGCM). The AGCM was forced with sea surface temperature (SST) anomalies in the tropical Pacific for the two El Niño events of 1997/1998 (EN97) and 2002/2003 (EN02). The strong eastern Pacific SST anomaly of EN97 resulted in a typical displacement of the Walker circulation, causing a decrease in precipitation across the north of South America. A strengthened low‐level jet (LLJ) east of the Andes during EN97 enhanced the moisture transport from low latitudes to the subtropics, leading to intensified precipitation over southeastern South America. The simulated circulation in EN02 reveals a weakened LLJ and anomalous convergence of moisture over eastern South America, which can be attributed to a displacement of the Pacific‐South American (PSA) mode in response to the different location of the heat sources along the tropical Pacific Ocean.

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Inter-El Niño variability and its impact on the South American low-level jet east of the Andes during austral summer − two case studies

Cited by 41 publications

References 18 publications

Observational evidences on the modulation of the South American Low Level Jet east of the Andes according the ENSO variability

Observational evidences on the modulation of the South American Low Level Jet east of the Andes according the ENSO variability

The Contribution of Mesoscale Convective Complexes to Rainfall across Subtropical South America

South American rainfall impacts associated with inter‐El Niño variations

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