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

2007 ◽  
Vol 135 (3) ◽  
pp. 1165-1174 ◽  
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.

scholarly journals Impact of enriched analyses on regional numerical forecasts over southeastern South America during SALLJEX

2014 ◽  
Vol 29 (3) ◽  
pp. 315-330
Author(s):  
Yanina García Skabar ◽  
Matilde Nicolini
Keyword(s):  
Data Assimilation ◽  
South America ◽  
Atmospheric Modeling ◽  
South American ◽  
The South ◽  
Low Level ◽  
Positive Effects ◽  
Accumulated Rainfall ◽  
Low Level Jet ◽  
The Impact

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.

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

2019 ◽  
Vol 124 (3) ◽  
pp. 1200-1218 ◽  
Author(s):  
Tessa L. Montini ◽  
Charles Jones ◽  
Leila M. V. Carvalho
Keyword(s):  
South American ◽  
The South ◽  
Low Level ◽  
Low Level Jet

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

2009 ◽  
Vol 27 (2) ◽  
pp. 645-657 ◽  
Author(s):  
G. A. M. Silva ◽  
T. Ambrizzi ◽  
J. A. Marengo
Keyword(s):  
South America ◽  
South American ◽  
The South ◽  
Trade Winds ◽  
La Plata ◽  
The Andes ◽  
La Plata Basin ◽  
Normal Frequency ◽  
Rainfall Anomalies ◽  
Low Level Jet

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 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.

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

2006 ◽  
Vol 6 ◽  
pp. 283-287 ◽  
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.

Orogenic Convection in Subtropical South America as Seen by the TRMM Satellite

2011 ◽  
Vol 139 (8) ◽  
pp. 2399-2420 ◽  
Author(s):  
Kristen L. Rasmussen ◽  
Robert A. Houze
Keyword(s):  
South America ◽  
Tropical Rainfall Measuring Mission ◽  
The United States ◽  
South American ◽  
Convective Storms ◽  
Mountain Ranges ◽  
Low Level ◽  
Global Understanding ◽  
Low Level Jet ◽  
Downslope Flow

AbstractExtreme orogenic convective storms in southeastern South America are divided into three categories: storms with deep convective cores, storms with wide convective cores, and storms containing broad stratiform regions. Data from the Tropical Rainfall Measuring Mission satellite’s Precipitation Radar show that storms with wide convective cores are the most frequent, tending to originate near the Sierra de Cordoba range. Downslope flow at upper levels caps a nocturnally enhanced low-level jet, thus preventing convection from breaking out until the jet hits a steep slope of terrain, such as the Sierra de Cordoba Mountains or Andean foothills, so that the moist low-level air is lifted enough to release the instability and overcome the cap. This capping and triggering is similar to the way intense convection is released near the northwestern Himalayas. However, the intense storms with wide convective cores over southeastern South America are unlike their Himalayan counterparts in that they exhibit leading-line/trailing-stratiform organization and are influenced by baroclinic troughs more similar to storms east of the Rocky Mountains in the United States. Comparison of South American storms containing wide convective cores with storms in other parts of the world contributes to a global understanding of how major mountain ranges influence precipitating cloud systems.

scholarly journals Characterizing the Diurnal Cycle of Low-Level Circulation and Convergence Using CFSR Data in Southeastern South America

2015 ◽  
Vol 54 (3) ◽  
pp. 671-690 ◽  
Author(s):  
Henrique Fuchs Bueno Repinaldo ◽  
Matilde Nicolini ◽  
Yanina García Skabar
Keyword(s):  
South America ◽  
Diurnal Cycle ◽  
Inertial Oscillation ◽  
South American ◽  
The South ◽  
Broad Perspective ◽  
Low Level ◽  
The Andes ◽  
Synoptic Conditions ◽  
Divergence Field

AbstractThe focus of this study is the characterization of the diurnal cycle of low-level wind and divergence field (under two different synoptic situations observed during the South American Low-Level Jet Experiment) within the South American domain encompassed between 20° and 35°S east of the Andes, using Climate Forecast System Reanalysis (CFSR). The objective is to highlight the existence of a spatial variation of these quantities and differences in the strength of their diurnal cycle between the two synoptic situations. Inertial oscillations and thermally driven circulations as well as convection-related contributions to mesoscale convergence and their implications for deep convection initiation/maintenance are addressed in each selected subregion. Prevalence of synoptic-scale forcing over the diurnally forced circulations, or vice versa, is also analyzed. Both mesoscale wind diurnal cycle and related divergence fields are sensitive to varying synoptic conditions and display regional variability. Thermal circulations related to topographical features superpose on the diurnal inertial oscillation that, while present in the whole domain, dominates the central plain subregions. The most evident diurnal cycle in the divergence field is restricted to sloped areas just to the east of the Andes and the Sierras de Córdoba where the mesoscale component of the divergence field is responsible for modulating the total divergence. CFSR provides a broad perspective of low-level circulation over southeastern South America (SESA) during the specific 15-day period. Results from this study might stimulate future research on a relationship between low-level circulation and the initiation of convection in SESA using CFSR to perform high-resolution simulations.

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

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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