RELATIONSHIPS BETWEEN PRECIPITATION ANOMALIES IN URUGUAY AND SOUTHERNBRAZIL AND SEA-SURFACE TEMPERATURE IN THE PACIFIC AND ATLANTIC OCEANS

This study focuses on precipitation in Uruguay and the Brazilian state of Rio Grande do Sul, which extend along the Atlantic coast of southe rn South America. The present paper has two principal goals: 1) to des cribe the annual cycle of precipitation and 2) to investigate the rela tionships between its anomalies and those in sea surface temperature ( SST) in the Pacific and Atlantic oceans. The dataset is provided by 40 rainfall stations almost evenly distributed in space and covers the p eriod 1917-80. The tools used in support of this research include prin cipal component and canonical correlation analyses. It is found that t otal precipitation tends to be evenly distributed during the year. The largest spatial variability in the monthly deviations from the annual mean appears as a west-east (inland-coastal) dipole with the largest positive values in the west during early fall and midspring, and in th e east along the Atlantic coast during winter. The second mode of rain fall variability appears as a north-south dipole with the largest posi tive values in the south during late summer and late fall, and in the north during early spring and early summer. The third mode appears pri marily as a north-south dipole along the western boundary with the lar gest positive values in the southwest during fall and in the northwest during early spring. These modes explain 60%, 19%, and 8% of the tota l variance. Five subregions are identified according to similarities b etween the characteristics of the annual cycles in their rainfall stat ions. It is shown that there are significant relationships between ano malies in rainfall and in SST in the Pacific and Atlantic oceans. Some of these relationships confirm the results of previous studies, such as the links between the El Nino-Southern Oscillation phenomenon in th e equatorial Pacific Ocean and rainfall anomalies in Uruguay during la te spring-early summer and late fall-early winter. Other relationships have not been reported before, such as the links between SST anomalie s in the southwestern Atlantic Ocean and rainfall anomalies in the ent ire region during October-December and April-July. Iris also found tha t when SST anomalies are considered in both oceans simultaneously, the ir links with rainfall anomalies are in some cases enhanced and in oth ers weakened.