Observational evidences on the modulation of the South American Low Level Jet east of the Andes according the ENSO variability
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 SALL...
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doaj-4a26b554aa824b0183ce0c9a6f4376302020-11-24T22:42:41ZengCopernicus PublicationsAnnales Geophysicae0992-76891432-05762009-02-012764565710.5194/angeo-27-645-2009Observational evidences on the modulation of the South American Low Level Jet east of the Andes according the ENSO variabilityG. A. M. Silva0T. Ambrizzi1J. A. Marengo2Department of Atmospheric Sciences, Institute of Astronomy, Geophysics and Atmospheric Sciences, University of São Paulo, São Paulo, BrazilDepartment of Atmospheric Sciences, Institute of Astronomy, Geophysics and Atmospheric Sciences, University of São Paulo, São Paulo, BrazilCenter for Weather Forecasts and Climate Studies, National Institute for Space Studies, Cachoeira Paulista, BrazilThe 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. <br><br> 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.https://www.ann-geophys.net/27/645/2009/angeo-27-645-2009.pdf |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
G. A. M. Silva T. Ambrizzi J. A. Marengo |
spellingShingle |
G. A. M. Silva T. Ambrizzi J. A. Marengo Observational evidences on the modulation of the South American Low Level Jet east of the Andes according the ENSO variability Annales Geophysicae |
author_facet |
G. A. M. Silva T. Ambrizzi J. A. Marengo |
author_sort |
G. A. M. Silva |
title |
Observational evidences on the modulation of the South American Low Level Jet east of the Andes according the ENSO variability |
title_short |
Observational evidences on the modulation of the South American Low Level Jet east of the Andes according the ENSO variability |
title_full |
Observational evidences on the modulation of the South American Low Level Jet east of the Andes according the ENSO variability |
title_fullStr |
Observational evidences on the modulation of the South American Low Level Jet east of the Andes according the ENSO variability |
title_full_unstemmed |
Observational evidences on the modulation of the South American Low Level Jet east of the Andes according the ENSO variability |
title_sort |
observational evidences on the modulation of the south american low level jet east of the andes according the enso variability |
publisher |
Copernicus Publications |
series |
Annales Geophysicae |
issn |
0992-7689 1432-0576 |
publishDate |
2009-02-01 |
description |
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.
<br><br>
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. |
url |
https://www.ann-geophys.net/27/645/2009/angeo-27-645-2009.pdf |
work_keys_str_mv |
AT gamsilva observationalevidencesonthemodulationofthesouthamericanlowleveljeteastoftheandesaccordingtheensovariability AT tambrizzi observationalevidencesonthemodulationofthesouthamericanlowleveljeteastoftheandesaccordingtheensovariability AT jamarengo observationalevidencesonthemodulationofthesouthamericanlowleveljeteastoftheandesaccordingtheensovariability |
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