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Equatorial Atlantic variability—Modes, mechanisms, and global teleconnections

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Sea surface temperature (SST) variability in the tropical Atlantic Ocean strongly impacts the climate on the surrounding continents. On interannual time scales, highest SST variability occurs in the eastern equatorial region and off the coast of southwestern Africa. The pattern of SST variability resembles the Pacific El Niño, but features notable differences, and has been discussed in the context of various climate modes, that is, reoccurring patterns resulting from particular interactions in the climate system. Here, we attempt to reconcile those different definitions, concluding that almost all of them are essentially describing the same mode that we refer to as the “Atlantic Niño.” We give an overview of the mechanisms that have been proposed to underlie this mode, and we discuss its interaction with other climate modes within and outside the tropical Atlantic. The impact of Atlantic Niño‐related SST variability on rainfall, in particular over the Gulf of Guinea and north eastern South America is also described. An important aspect we highlight is that the Atlantic Niño and its teleconnections are not stationary, but subject to multidecadal modulations. Simulating the Atlantic Niño proves a challenge for state‐of‐the‐art climate models, and this may be partly due to the large mean state biases in the region. Potential reasons for these model biases and implications for seasonal prediction are discussed. This article is categorized under: Climate Models and Modeling > Knowledge Generation with Models
Schematic diagram of the different mechanisms suggested to generate Atlantic Niño events: (a) the Bjerknes feedback including a weakening of the trade winds and adjustments of the thermocline slope via the propagation of equatorial Kelvin waves; (b) meridional advection of temperature anomalies; (c) Rossby wave reflection; (d) equatorial deep jets; and (e) net surface heat flux anomalies
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Pattern and time evolution of interannual sea surface temperature (SST) variability in the tropical Atlantic from monthly National Oceanic and Atmospheric Administration (NOAA) optimum interpolation (OI) SST (Reynolds, Rayner, Smith, Stokes, & Wang, ) for the time period 1982–2016. (a) Standard deviation (shading) of interannual SST anomalies and annual mean climatological SST (contours). Contour interval is 0.5 °C with 27 °C line in bold. (b) First EOF of interannual SST anomalies in the region 60°W to 20°E, 20°S to 20°N (shading) and associated wind anomalies (vectors). First EOF explains 32% of the variance. (c) Principal component of first EOF (black) and SST anomalies in °C averaged over ATL3 region (20°W to 0°E, 3°S to 3°N, indicated as blue box in (a), red). (d) Seasonal cycle of ATL3 SST (black) and standard deviation of interannual SST anomalies (blue)
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Simulation of tropical Atlantic sea surface temperature (SST) in climate models. (a) SST bias (K) in an ensemble mean of models from the CMIP5 experiment piControl. The reference data is NOAA optimum interpolation (OI) SST for the period 1982–2016. (b) and (c) Longitude time sections of SST (°C; shading) and its standard deviation (K; contours), averaged between 3°S and 3°N for OISST (b) and CMIP5 (c)
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Decadal modulation of Atlantic–Pacific relationship. Running correlation of 20‐yr windows between the boreal summer (JJAS) sea surface temperature (SST) anomalies in ATL3 region (20°W to 0°E, 3°N to 3°S) and the following boreal winter (DJFM) SST anomalies in Niño3 (150°W to 90°W, 5°N to 5°S) (blue line), boreal summer (JASO) precipitation in western equatorial Atlantic (70°W to 35°W, 5°N to 5°S) (red line) and boreal summer (JASO) zonal surface wind in western equatorial Pacific (140°E to 180°, 5°N to 5°S) (green line). Dots denoted significant correlations according to a t test at 95% confidence level
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Decadal change of the Atlantic Niño pattern and its impact. SST anomalies of the Atlantic Niño pattern during boreal summer before (a) and after (b) the 1970s and a schematic representation of the respective impact on the Pacific and Indian Oceans
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