Influência do El Niño-Oscilação Sul sobre a precipitação na América do Sul: Eventos anuais versus multianuais (intensificados versus persistentes)

Abstract

Based on reanalysis data and seasonal composition analysis, were investigated the influence of El Niño–Southern Oscillation (ENSO) events over South American (SA) precipitation, considering the duration and intensity of maximum Sea Surface Temperature (SST) anomalies in Central Pacific for the period 1901–2012. ENSO events were initially classified based on their duration as either single-year and multiyear events. For El Niño conditions, a single-year event starts in austral winter, reaches its peak in summer, and rapidly declines in the following autumn. In contrast, a multiyear event starts in winter, peaks in summer, weakens in autumn, and persists until the following summer. Additionally, multiyear events exhibit differences in peak intensities during consecutive summers, leading to further classification as intensified and persistent multiyear events. In the case of intensified [persistent] events, the weak-to-moderate [strong] positive SST anomalies observed in the first summer, slightly weaken [dramatically] in the following autumn, intensify [persist] until the second summer, and decline rapidly [slowly] in the subsequent autumn. These varying SST anomalies in the Central Pacific trigger different modes of climatic variability in the tropical Indian and Atlantic Oceans through large-scale circulations, consequently resulting in distinct precipitation patterns in SA. Contrasting single-year with multiyear events, we observed that the seasonal precipitation patterns exhibit the typical north/south dipole with rainfall deficit/excess, respectively, in all seasons of single-year events. On the other hand, during multiyear events, differences in the intensity and positioning of negative precipitation anomalies occur in the northern and northeastern regions of SA in all seasons. Moreover, wet conditions tend to be displaced further south in SA during the second year of multiyear events. However, unlike the overall behavior of multiyear events, rainfall anomalies during the first year of intensified [persistent] events exhibit differences [similarities] in positioning and are more intense than those during the second year. Generally, negative precipitation anomalies in the northwest, north, and northeast of SA are influenced by the positioning and intensity of the downward motions of Walker circulation in these regions, while positive anomalies are modulated by Rossby-wave trains patterns and changes in regional atmospheric circulation. Our results elucidate the various physical mechanisms associated with significant rainfall variability in SA and may be useful for monitoring and forecasting local and regional impacts.