Large-Scale Circulation Anomalies and the Predictability of Northeast Brazil Droughts

摘要

An analysis of the monthly departure of the relative vorticity and wind fields over the globe was performed for the period from 1963 to 1980. Planetary-scale wavelike (teleconnection) patterns were observed in the vorticity and wind deviation fields extending from subtropical North Atlantic through the North Pole to eastern Siberia for years of droughts and excessive rainfall over Northeast Brazil (Nordeste). These patterns are sharpest in December and January. Of major interest is the phase coherence of the wavelike patterns and the precipitation anomalies of Nordeste, that is, the phase of the patterns is reversed from very dray to very wet years. Such phase coherence and also the emergence and persistence of the wavelike pattern several months preceding the rainy season in Nordeste (March and May), seems to indicate that there might be some predictive potential in these configurations. An index of the existence and phase of the wavelike patterns was developed. It was seen that the sign of the index is highly associated with the sign of the precipitation anomaly in Nordeste for most of the years.