Thermodynamic controls of the Atlantic Nino

Prevailing theories on the equatorial Atlantic Nino are based on the dynamical interaction between atmosphere and ocean. However, dynamical coupled ocean-atmosphere models poorly simulate and predict equatorial Atlantic climate variability. Here we use multi-model numerical experiments to show that thermodynamic feedbacks excited by stochastic atmospheric perturbations can generate Atlantic Nino s.d. of similar to 0.28 +/- 0.07 K, explaining similar to 68 +/- 23% of the observed interannual variability. Thus, in state-of-the-art coupled models, Atlantic Nino variability strongly depends on the thermodynamic component (R-2 = 0.92). Coupled dynamics acts to improve the characteristic Nino-like spatial structure but not necessarily the variance. Perturbations of the equatorial Atlantic trade winds (similar to +/- 1.53ms(-1)) can drive changes in surface latent heat flux (similar to +/- 14.35 Wm(-2)) and thus in surface temperature consistent with a first-order autoregressive process. By challenging the dynamical paradigm of equatorial Atlantic variability, our findings suggest that the current theories on its modelling and predictability must be revised.