The South American Low-Level Jet: A New Climatology, Variability, and Changes

During the warm season 2002-2003, the South American Low-Level Jet Experiment (SALLJEX) was carried out in southeastern South America. Taking advantage of the unique database collected in the region, a set of analyses is generated for the SALLJEX period assimilating all available data. The spatial and temporal resolution of this new set of analyses is higher than that of analyses available up to present for southeastern South America. The aim of this paper is to determine the impact of assimilating data into initial fields on mesoscale forecasts in the region, using the Brazilian Regional Atmospheric Modeling System (BRAMS) with particular emphasis on the South American Low-Level Jet (SALLJ) structure and on rainfall forecasts. For most variables, using analyses with data assimilated as initial fields has positive effects on short term forecast. Such effect is greater in wind variables, but not significant in forecasts longer than 24 hours. In particular, data assimilation does not improve forecasts of 24-hour accumulated rainfall, but it has slight positive effects on accumulated rainfall between 6 and 12 forecast hours. As the main focus is on the representation of the SALLJ, the effect of data assimilation in its forecast was explored. Results show that SALLJ is fairly predictable however assimilating additional observation data has small impact on the forecast of SALLJ timing and intensity. The strength of the SALLJ is underestimated independently of data assimilation. However, Root mean square error (RMSE) and BIAS values reveal the positive effect of data assimilation up to 18-hours forecasts with a greater impact near higher topography.

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The Nature of a Heat Wave in Eastern Argentina Occurring during SALLJEX

Monthly Weather Review ◽

10.1175/mwr3306.1 ◽

2007 ◽

Vol 135 (3) ◽

pp. 1165-1174 ◽

Cited By ~ 16

Author(s):

S. Bibiana Cerne ◽

Carolina S. Vera ◽

Brant Liebmann

Keyword(s):

South America ◽

Heat Wave ◽

Strong Impact ◽

South American ◽

Atmospheric Conditions ◽

The South ◽

Low Level ◽

Central Argentina ◽

Temperature Advection ◽

Low Level Jet

Abstract This note describes the physical processes associated with the occurrence of a heat wave over central Argentina during the austral summer of 2002/03, during which the South American Low-Level Jet Experiment (SALLJEX) was carried out. The SALLJEX heat wave that lasted between 25 January and 2 February 2003 was punctuated by extreme conditions during its last 3 days, with the highest temperature recorded over the last 35 yr at several stations of the region. It was found that not only the activity of synoptic-scale waves, but also the intraseasonal oscillation variability, had a strong impact on the temperature evolution during this summer. During the weeks previous to the heat wave development, an intensified South Atlantic convergence zone (SACZ) dominated the atmospheric conditions over tropical South America. Temperatures started to increase in the subtropics due to the subsidence and diabatic warming associated with the SACZ, as depicted by SALLJEX upper-air observations. An extratropical anticyclone that evolved along southern South America further intensified subsidence conditions. By the end of January the warming processes associated with SACZ activity weakened, while horizontal temperature advection began to dominate over central Argentina due to the intensification of the South American low-level jet. This mechanism led to temperature extremes by 2 February with temperature anomalies at least two standard deviations larger than the climatological mean values. Intense solar heating favored by strong subsidence was responsible for the heat wave until 31 January, after which horizontal temperature advection was the primary process associated with the temperature peak.

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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

Advances in Geosciences ◽

10.5194/adgeo-6-283-2006 ◽

2006 ◽

Vol 6 ◽

pp. 283-287 ◽

Cited By ~ 20

Author(s):

G. A. M. Silva ◽

T. Ambrizzi

Keyword(s):

El Niño ◽

El Nino ◽

Austral Summer ◽

South American ◽

The South ◽

Trade Winds ◽

Low Level ◽

The Andes ◽

Low Level Jet ◽

The Impact

Abstract. The impact of the maximum convection location over eastern and central Equatorial Pacific over the intensity and positioning of the South American Low-Level Jet east of the Andes (SALLJ) during the austral summer was investigated. The Bonner criteria 1 was applied to the NCEP-NCAR circulation fields during the El Niño of 1997/1998 and 2002/2003 to identify the SALLJ episodes. The composites of the atmospheric circulation over the South America during El Niño events showed that the SALLJ can be influenced by small displacements of the quasi-stationary Rossby waves position. During the strong El Niño event of 1997/1998 the SALLJ is maintained by the eastern trade winds. A low-level anomalous anticyclonic circulation over the central part of Brazil enhanced the wind in the nucleus of the jet and displaced its axis to the Northern Argentina and South of Brazil. However, the northern trade winds seem to maintain the SALLJ during the weak El Niño of 2002/2003. The jet was weaker and displaced more southeastward of Brazil than during the strong event.

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The South American low-level jet east of the Andes during the 1999 LBA-TRMM and LBA-WET AMC campaign

Journal of Geophysical Research Atmospheres ◽

10.1029/2001jd001188 ◽

2002 ◽

Vol 107 (D20) ◽

Cited By ~ 58

Author(s):

Jose A. Marengo

Keyword(s):

South American ◽

The South ◽

Low Level ◽

The Andes ◽

Low Level Jet

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Variability of the low-level circulation of the South American Monsoon analysed with complex networks

The European Physical Journal Special Topics ◽

10.1140/epjs/s11734-021-00187-w ◽

2021 ◽

Author(s):

Maximilian Gelbrecht ◽

Niklas Boers ◽

Jürgen Kurths

Keyword(s):

El Niño ◽

El Nino ◽

Wind Flow ◽

South American ◽

The South ◽

Local Flow ◽

Low Level ◽

South American Monsoon ◽

Low Level Jet ◽

The Impact

AbstractUnderstanding the variability of low-level atmospheric circulation regimes is key for understanding the dynamics of monsoon systems. The South American Monsoon is characterized by strong year-long trade winds that are channeled southward into the South American Low-Level Jet after crossing the Amazon basin, which in turn is elementary for the moisture transport to Southern South America. In this study, we utilize streamflow wind networks, a type of climate networks that tracks the local flow of the wind field, together with the analysis of composites of wind, precipitation, and geopotential height fields, to investigate the variability of the South American low-level circulation. The streamflow wind networks are used here as they are able to directly track the wind flow and encode its spatiotemporal characteristics in their topology. We focus on intraseasonal variations in terms of active and break monsoon phases on the one hand, and on the interannual variability in terms of the impacts of the El Niño-Southern Oscillation on the other hand. Our findings highlight the importance of the South American Low-Level Jet, its spatial position and variability. Our study reveals the relation of the active and break regimes to anomalous high- and low-pressure systems over the southern Atlantic that are connected to Rossby wave trains from the southern Pacific, as well as the impact of these regimes on the cross-equatorial low-level flow. In addition, the streamflow networks that we use demonstrate significant shifts of the dominant wind flow pattern during El Niño and La Niña episodes.

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