The influence of the Pacific and Atlantic ssts in the South America monsoon rainfall / A influência das TSMS dos ocenos Pacíficos e Atlântico nas chuvas de monção da América do Sul

AUTOR(ES)
DATA DE PUBLICAÇÃO

2000

RESUMO

Monthly information of outgoing long wave radiation (OLR), sea surface temperature (SST), and rainfall from 22 meteorological stations in eastern South America were used to identify the rainfall characteristics of the South American Monsoon systems (SAMS). The 1961-1999 rainfall climatology for the area allowed the identification of two seasons with marked precipitation regimes: a well defined rainy season in December, January and February, and a dry season in June, July and August. The period where the summer monsoon in South America is more intense was identified from September- February, and this can hold up to 80% of the annual total rainfall. The onset of the rainy season as estimated from outgoing long wave radiation pentad climatology 1974-1996 showed that on the northeastern part of the monsoon area, rainy seasons are shorter as compared to the rest of the region. The dates of the onset of the rainy season during the whole period 1974-1996 show large interannual variability, that does not seem to be related to El Niño or La Niña. The correlation analysis between sea surface temperature anomalies and rainfall in the monsoon area, represented by the Summer Monsoon Rainfall Index (IMV), show that both Atlantic and Pacific affect the variability of rainfall on the region. In the Pacific, 4 areas that may exert some influence on the IMV were identified: Niño 3.4-Niño 4, Chilean central coast, south central Pacific and the western Pacific of Northeast of Australia. This influence can be related to an atmospheric-oceanic coupling, that favours the propagation of Rossby waves that affect the South Atlantic Convergence Zone and possibly the monsoon rainfall variability. In the Pacific Ocean, correlation fields exhibit a North-South dipole type pattern that lasts at least 4 months (July- October), followed by a region of negative correlations between November and December. On the Atlantic, the band of negative SST-rainfall correlations between 5° and 20°S can be explained through the intensification of the winds related to these SST anomalies, which entails a stronger moisture transport into the continent and thus an increment of rains on this area. In addition, an effect of convection and latent heat release in Amazonia combined with modifications in the intensity-location of the Bolivian high can also affect moisture transport from this region to the monsoon area, thus affecting the intensity of the summer rains on the monsoon area.

ASSUNTO(S)

monções américa do sul tropical region região tropical summer climatologia. key words: monsson verão climatology south america

ACESSO AO ARTIGO

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