On the Spatiotemporal Diversity of Atlantic Niño and Associated Rainfall Variability Over West Africa and South America

Abstract

Warm phases of the Atlantic Zonal Mode (AZM), known as Atlantic Niño (AN), are caused by a variety of mechanisms. In this study we analyze the diversity of AN-events through an inter-event empirical orthogonal function (EOF) methodology. The first two orthogonal modes, which explain 30% and 24% of the inter-annual variability, allow describing four of the principal spatio-temporal patterns in sea surface temperature (SST). The first two contrast the timing of dissipation (i.e., early-terminating versus persistent), while the other two the timing of onset (i.e., early-onset versus late-onset). Largely consistent with the differences in the timings of onset and dissipation, these four varieties display remarkable differences in rainfall response over West Africa and South America. Some are also subject to onset mechanisms that involve preconditioning in boreal spring from the Atlantic Meridional Mode or El Niño in the Pacific, while for others there is no clear source of external forcing