Impacts of the Oscillation on the intensity and spatial extent of heavy precipitation events in northern Northeast Brazil.

Abstract

This paper investigates the spatiotemporal variability of Contiguous ExtremePrecipitation Events (CEPE) related to Madden-Julian Oscillation (MJO) activ-ity during the pre-wet season and wet season in northern Northeast Brazil for30 years (1979–2010). Inherent differences in rainy season regimes are associ-ated with northern Northeast Brazil precipitation systems; these are isolatedduring pre-wet and wet season and analyse the intensity and the spatial areacovered by the CEPE. A daily index of MJO activity and its life cycle were usedto identify activity phases during heavy rainfall events. Composite analysis wasperformed for days with CEPE during the most frequent MJO phases in thepre-wet and wet seasons. The analysis shows the influence of the MJO onthe occurrence of CEPE in northern Northeast Brazil. In the pre-wet season,the MJO phases 8-1-2 affect the occurrence of heavy rainfall events,modifying the atmospheric circulation and water vapour transport over north-ern South America. Indications of Rossby wave propagation over the SouthPacific associated with MJO were found, suggesting tropic-extratropic tele-connection during occurrences of CEPE in the pre-wet season. In the wet sea-son, CEPE events are more frequent during MJO phases 8-2-3. Conversely, nowave propagation over the South Pacific is observed in the wet season, changesin wind anomalies at high and low atmospheric levels only point to the influ-ence of the MJO via tropical teleconnection. This study may help monitoringand forecasting of very heavy rainfall events in northern Northeast Brazil inpre-wet season and wet season.