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

• Published in: Geophysical research letters 2020-04, Vol.47 (8), p.n/a
• Main Authors: Vallès‐Casanova, Ignasi, Lee, Sang‐Ki, Foltz, Gregory R., Pelegrí, Josep L.
• Format: Article
• Language: English
• Subjects: Anomalies; Atlantic Niño diversity; Atlantic zonal mode; El Nino; El Nino phenomena; Empirical analysis; Flooding; Function analysis; Orthogonal functions; Preconditioning; Rain; Rainfall; Rainfall variability; Sea surface; Sea surface temperature; Sea surface temperature anomalies; Socioeconomic factors; South American rainfall; Spring; Spring (season); Surface temperature; Temperature anomalies; tropical Atlantic variability; Variability; West African monsoon; West African rainfall
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2020GL087108

The spatiotemporal evolutions of equatorial Atlantic sea surface temperature anomalies (SSTAs) during Atlantic Niño events and the associated climate impacts on the surrounding continents are extremely diverse. In this study, we construct longitude‐time maps of equatorial Atlantic SSTAs for each observed Atlantic Niño event during 1948–2019 and perform a spatiotemporal empirical orthogonal function analysis to identify the four most frequently recurring Atlantic Niño varieties. The first two contrast the timing of dissipation (early terminating vs. persistent) and the other two the timing of onset (early onset vs. 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. Most of the varieties are subject to onset mechanisms that involve preconditioning in boreal spring by either the Atlantic meridional mode or Pacific El Niño, while for the late onset variability there is no clear source of external forcing. Plain Language Summary A phenomenon known as Atlantic Niño is characterized by the appearance of warm sea surface temperature anomalies (SSTAs) in the eastern equatorial Atlantic in northern summer. When it attains its full strength, it increases rainfall and the frequency of extreme flooding over the West African countries bordering the Gulf of Guinea and in northeastern South America. Atlantic Niño thus has a direct socioeconomic impact in emerging countries in these regions. However, not all Atlantic Niño events are alike. Some appear earlier than others or persists longer. These variabilities during the onset and dissipation phases are well captured by the four most recurring Atlantic Niño varieties identified in this study. 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. Most of the varieties are subject to preconditioning in northern spring by cold SSTAs in the North Atlantic or El Niño in the Pacific, except for one variety with no clear source of external forcing. Key Points A systematic statistical analysis identifies the four most frequently recurring Atlantic Niño varieties during 1948–2019 Due to the differences in the timings of onset and dissipation, they display large differences in rainfall over West Africa and South America Most of the varieties are prec