PRECIPITATION ANOMALIES IN SOUTHERN BRAZIL ASSOCIATED WITH EL-NINO AND LA NINA EVENTS

The impact of El Nino and La Nina events (warm and cold phases of the Southern Oscillation) on rainfall over southern Brazil is investigated through the use of a large dataset of monthly precipitation from 250 stations. This region is partly dominated by rough orography and prese nts different climatic regimes of rainfall. As previous global studies on Southern Oscillation-precipitation relationships used data from on ly two stations in southern Brazil, this region was not included in th e area of consistent Southern Oscillation-related precipitation in sou theastern South America. The present analysis is based on the method b y Ropelewski and Halpert, the sensitivity of which is assessed for thi s region. The spatial structure of the rainfall anomalies associated w ith warm (cold) events is analyzed and subregions with coherent anomal ies are determined. Their distribution indicates the influence of reli ef, latitude, and proximity to the ocean. These areas are subjected to further analysis to determine the seasons of largest anomalies and as sess their consistency during warm (cold) events. The whole of souther n Brazil was found to have strong and consistent precipitation anomali es associated with those events. Their magnitude is even larger than i n Argentina and Uruguay. All of the subregions have consistent wet ano malies during the austral spring of the warm event year, with a pronou nced peak in November. The southeastern part also shows a consistent t endency to higher than average rainfall during the austral winter of t he following year. There is also a consistent tendency to dryness in t he year before a warm event. During the spring of cold event years str ong consistent dry anomalies prevail over the whole region, also with maximum magnitude in November. They are even stronger and more consist ent than the wet anomalies in warm event years. Consistent anomalies d o not occur over large areas in the years before and after cold events . The wet anomalies during the austral spring of the warm event year w eaken and even reverse during the following January. The same tendency , though not so clear, is observable in the dry anomalies of cold even ts. The seasons of largest anomalies disclosed by this study differ fr om those found by previous global studies for other regions in southea stern South America. This study expands the area of consistent warm (c old) event-related precipitation defined by previous studies in southe astern South America by including a region of larger anomalies, and pr ovides a spatial and temporal refinement to the warm (cold) event-prec ipitation relationship.