INTERANNUAL VARIABILITY OF SURFACE CLIMATE IN THE AMAZON BASIN

This empirical study examines the circulation mechanisms of anomalously wet and dry years in the Amazon basin. Data sources include surface ship observations in the tropical Atlantic, eastern Pacific, and Indian Oceans, as well as various hydrometeorological indices in Amazonia during 1951 1983. Rainfall and river water level anomalies in northern Amazonia are associated with distinct circulation patterns in the tropical Atlantic, particularly at the March April peak of the rainy season. Thus, abundant rainfall in northern Amazonia and high Rio Negro water levels are accompanied by a strong North Atlantic high, steep meridional pressure gradient on its equatorward side, accelerated North-east trades, and cool surface waters in the tropical North Atlantic. The intensified North-east trades may entail enhanced boundary-layer moisture transport from the tropical North Atlantic into the Amazon basin. This ensemble of atmospheric and oceanic anomalies is characteristic of, but not limited to, the high phase of the Southern Oscillation (defined by anomalously high/low pressure at Tahiti/Darwin).