Diabatic heating governs the seasonality of the Atlantic Niño.

The Atlantic Nino is the leading mode of interannual sea-surface temperature (SST) variability in the equatorial Atlantic and assumed to be largely governed by coupled ocean-atmosphere dynamics described by the Bjerknes-feedback loop. However, the role of the atmospheric diabatic heating, which can be either an indicator of the atmosphere’s response to, or its influence on the SST, is poorly understood. Here, using satellite-era observations from 1982–2015, we show that diabatic heating variability associated with the seasonal migration of the Inter-Tropical Convergence Zone controls the seasonality of the Atlantic Nino. The variability in precipitation, a measure of vertically integrated diabatic heating, leads that in SST, whereas the atmospheric response to SST variability is relatively weak. Our findings imply that the oceanic impact on the atmosphere is smaller than previously thought, questioning the relevance of the classical Bjerknes-feedback loop for the Atlantic Nino and limiting climate predictability over the equatorial Atlantic sector. The relative roles of the ocean and atmosphere for the Atlantic Nino is poorly understood. Here, we show that its seasonality is governed by atmospheric diabatic heating that is associated with the seasonal migration of the inter-tropical convergence zone.