| Full text | |
| Author(s): |
Total Authors: 3
|
| Affiliation: | [1] Univ Sao Paulo, Dept Atmospher Sci, Inst Astron Geophys & Atmospher Sci, Sao Paulo - Brazil
[2] Natl Inst Space Studies, Ctr Weather Forecasts & Climate Studies, Cachoeira Paulista - Brazil
Total Affiliations: 2
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| Document type: | Journal article |
| Source: | Annales Geophysicae; v. 27, n. 2, p. 645-657, 2009. |
| Web of Science Citations: | 21 |
| Abstract | |
The differences on the phase and wavelength of the quasi-stationary waves over the South America generated by El Nino (EN) and La Nina (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 degrees 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. (AU) | |
| FAPESP's process: | 01/13816-1 - Brazilian component of the South American low level jet east of the Andes field experiment: interaction in meso and large scale between the Amazon and La Plata River Basins |
| Grantee: | Jose Antonio Marengo Orsini |
| Support Opportunities: | Research Projects - Thematic Grants |
| FAPESP's process: | 05/01804-0 - Influence of the internal variability on the dynamic associated with low-level jet to the east of the Andes and cold fronts during the southern Summer and Winter |
| Grantee: | Gyrlene Aparecida Mendes da Silva |
| Support Opportunities: | Scholarships in Brazil - Doctorate |