The influence of the Andes mountains on the South American low-level flow

AbstractEight South American geographical populations of the parasitoidMicroctonus hyperodaeLoan were collected in South America (Argentina, Brazil, Chile and Uruguay) and released in New Zealand for biological control of the weevilListronotus bonariensis(Kuschel), a pest of pasture grasses and cereals. DNA sequencing (16S, COI, 28S, ITS1, β-tubulin), RAPD, AFLP, microsatellite, SSCP and RFLP analyses were used to seek markers for discriminating between the South American populations. All of the South American populations were more homogeneous than expected. However, variation in microsatellites and 16S gene sequences corroborated morphological, allozyme and other phenotypic evidence of trans-Andes variation between the populations. The Chilean populations were the most genetically variable, while the variation present on the eastern side of the Andes mountains was a subset of that observed in Chile.

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

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-14-0114.1 ◽

2015 ◽

Vol 54 (3) ◽

pp. 671-690 ◽

Cited By ~ 7

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.

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Low-Level Jets and Their Effects on the South American Summer Climate as Simulated by the NCEP Eta Model*

Journal of Climate ◽

10.1175/1520-0442(2003)016<0297:lljate>2.0.co;2 ◽

2003 ◽

Vol 16 (2) ◽

pp. 297-311 ◽

Cited By ~ 33

Author(s):

Anandu D. Vernekar ◽

Ben P. Kirtman ◽

Michael J. Fennessy

Keyword(s):

South American ◽

The South ◽

Low Level ◽

Summer Climate ◽

Eta Model ◽

Low Level Jets

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

Revista Brasileira de Meteorologia ◽

10.1590/0102-778620100248 ◽

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.

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On the Pleistocene Snow-Line Depression in the Arid Regions of the South American Andes

Journal of Glaciology ◽

10.3189/s0022143000013228 ◽

1971 ◽

Vol 10 (59) ◽

pp. 255-267

Author(s):

Stefan L. Hastenrath

Keyword(s):

Arid Regions ◽

South American ◽

The South ◽

Temperate Latitude ◽

The Andes ◽

Western Cordillera ◽

Snow Line ◽

The Pacific ◽

The Arid Regions ◽

June July

AbstractField observations during a journey through the arid regions of the South American Andes in June-July 1969 are evaluated in conjunction with available air photographs and reports from adjacent regions of the High Andes. Results indicate an increase of the Pleistocene snow-line depression in the western Cordillera from about 700 m at lat. 12° S. to more than 1 500 m at lat. 30° S. The Pleistocene snow-line depression decreases from the Pacific to the Atlantic side of the Andes, but particularly strongly so on the poleward fringe of the arid region. From this geomorphic evidence it is suggested that the atmospheric circulation during the glacial period was characterized by an Equatorward displacement of the boundary between tropical easterlies and temperate-latitude westerlies.

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Analysis of Possible Triggering Mechanisms of Severe Thunderstorms in the Tropical Central Andes of Peru, Mantaro Valley

Atmosphere ◽

10.3390/atmos10060301 ◽

2019 ◽

Vol 10 (6) ◽

pp. 301 ◽

Cited By ~ 9

Author(s):

J.L. J.L. ◽

A.S. A.S. ◽

S. S. ◽

D. D. ◽

E. E. ◽

...

Keyword(s):

Central Andes ◽

The South ◽

The West ◽

Subtropical Anticyclone ◽

Low Level ◽

The Andes ◽

Severe Thunderstorms ◽

Westerly Winds ◽

Moisture Fluxes ◽

Triggering Mechanisms

The aim of the present study is to analyze the triggering mechanisms of three thunderstorms (TSs) associated with severe rainfall, hail and lightening in the tropical central Andes of Peru, specifically above the Huancayo observatory (12.04 ∘ S, 75.32 ∘ W, 3313 m a.s.l.) located in the Mantaro valley during the spring-summer season (2015–2016). For this purpose, we used a set of in-situ pluviometric observations, satellite remote sensing data, the Compact Meteorological Ka-Band Cloud Radar (MIRA-35C), the Boundary Layer Tropospheric Radar and downscaling model simulations with the Weather Research and Forecasting (WRF) Model (resolutions: 18 km, 6 km and 2 km), and the Advance Regional Prediction System (ARPS) (resolution: 0.5 km) models in order to analyze the dynamic of the atmosphere in the synoptic, meso and local scales processes that control the occurrence of the three TS events. The results show that at synoptic scale, the TSs are characterized by the southern displacement of the South-east Pacific Subtropical Anticyclone up to latitudes higher than 35 ∘ S, by the weakening and south-eastern displacement of the Bolivian high–North east low system and by the intrusion of westerly winds along the west side of the central Andes at upper and medium levels of the atmosphere. At meso-scale, apparently, two important moisture fluxes from opposite directions are filtered through the passes along the Andes: one from the north-west and the other from the south-east directions converge and trigger the deep convection into the Mantaro valley. These moisture fluxes are generated by the intrusion of the sea-breeze from the Pacific ocean along the west of the Andes coupling with upper and middle westerly winds and by the thermally induced moisture fluxes coming from the South American low level jet at the east side of the Andes. At the local scale, there is a low-level conditional instability in the previous hours as well as during the occurrence of the TSs above the Huancayo observatory. In addition, the simulation results indicated the possibility of generation of inertial gravity waves in the Amazon basin, associated with geostrophic adjustment which transports energy and moisture into the central Andes plateau and consequently intensifies the thunderstorms above the Mantaro valley.

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