Climatology of Polar Waves over South America: Sea Surface Temperature and Other Influences.

MÜLLER GABRIELA V; PEZZA, ALEXANDRE.; AMBRIZZI, TÉRCIO.

CPTEC, Cachoeira Paulista, Brasil.

Workshop; I Workshop on Extreme Climatic Events in South America: tropics-extratropics links during modern and past times.; 2001

Institut de Recherche pour le Développement, Universidade de São Paulo, Instituto de Geociências, Dpto. Geologia Sedimentar e Ambiental, e Centro de Previsão de Tempo e Estudos Climáticos (CPTEC/INPE).

This work shows some results on wintertime cold waves over the subtropical regions of South America. We produced SST composites associated with colder than normal and warmer than normal winters in São Paulo, on the average, using data from the IAG/USP meteorological station from 1950 to 1996. Relative humidity, precipitation and number of days with rainfall were also used in an attempt to verify a possible correlation with the SST anomalies. We believe that the humidity is an important component because of its influence on the radiational cooling process associated with polar waves. Finally, some frost composites were also made considering the principle that cold winters on the average are not necessarily frost winters, in São Paulo. The results suggest that there is a significant positive correlation between the SST anomalies over the subtropical Atlantic and the Equatorial Pacific near the South American coast and temperature anomalies in São Paulo. Furthermore, we showed that when the Equatorial Pacific is colder than normal, and the subtropical Atlantic is warmer than normal, São Paulo seems to present temperatures warmer than normal. Meanwhile, when the Equatorial Pacific is warmer than normal and the subtropical Atlantic is near or slightly below normal, there is a high probability of frost occurrence during July. Through the humidity analysis, we showed that El Niño years are rather associated with above normal precipitation in São Paulo. The opposite is valid during La Niña years. These features are consistent with previous works in the literature, showing a reasonable agreement with theoretical aspects addressing baroclinic Rossby wave propagation.