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| Titel |
Observational evidences on the modulation of the South American Low Level Jet east of the Andes according the ENSO variability |
| VerfasserIn |
G. A. M. Silva, T. Ambrizzi, J. A. Marengo |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 27, no. 2 ; Nr. 27, no. 2 (2009-02-11), S.645-657 |
| Datensatznummer |
250016404
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| Publikation (Nr.) |
 copernicus.org/angeo-27-645-2009.pdf |
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| Zusammenfassung |
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. |
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