[A-CG35] Multi-scale ocean-atmosphere interaction in the tropics

[ACG35-11] On the Spatiotemporal Diversity of Atlantic Niño and Associated Rainfall Variability Over West Africa and South America

★Invited Papers

*Ignasi Valles Casanova^1,2, Sang-Ki Lee³, Gregory Foltz³, Josep Lluís Pelegrí¹ (1.ICM-CSIC, 2.HUCS-HUJI, 3.NOAA-AOML)

Keywords:Tropical Atlantic Variability, ENSO, West Africa monsoon

The dynamics of the tropical Atlantic depend on complex local and remote ocean-atmosphere interactions at multiple spatial and temporal scales. Superimposed on seasonal fluctuations, the leading mode of interannual variability can disrupt the climatology of the equatorial Atlantic with important climatic implications in regions such as the Sahel and the Guinea Gulf in Western Africa. This mode of interannual variability, commonly known as the Atlantic Niño, is characterized by anomalous warm sea surface temperature (SSTAs) in the equatorial Atlantic. Moreover, its spatiotemporal evolution and the associated climate impacts on the surrounding continents are extremely diverse caused by a variety of mechanisms. In this study we construct longitude-time maps of 22 Atlantic Niños 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 timing of onset and dissipation, the four varieties display remarkable differences in climate response over Western Africa and South America. Further regression analysis suggests that most of the varieties are subject to onset mechanisms that involve preconditioning in boreal spring by either negative phase of Atlantic Meridional Mode (AMM) or el Niño in the Pacific.