Abstract
Prevailing theories on the equatorial Atlantic Niño 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 Niño s.d. of ∼0.28±0.07 K, explaining ∼68±23% of the observed interannual variability. Thus, in state-of-the-art coupled models, Atlantic Niño variability strongly depends on the thermodynamic component (R2=0.92). Coupled dynamics acts to improve the characteristic Niño-like spatial structure but not necessarily the variance. Perturbations of the equatorial Atlantic trade winds (∼±1.53 m s−1) can drive changes in surface latent heat flux (∼±14.35 W m−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.
Highlights
Prevailing theories on the equatorial Atlantic Nino are based on the dynamical interaction between atmosphere and ocean
The first set of experiments is based on state-of-the-art, fully coupled general circulation models (CGCMs), and in the second set, dynamical feedbacks are disabled by thermodynamically coupling the atmosphere to a 50-m deep slab of motionless ocean
We first examine the relationship between the Atlantic Nino sea surface temperature (SST) anomaly {SST}’ during its peak season of boreal summer and the preceding season near surface {u}’ over the western equatorial Atlantic Ocean as a measure of Bjerknes feedback in the fullCGCMs
Summary
Prevailing theories on the equatorial Atlantic Nino are based on the dynamical interaction between atmosphere and ocean. Dynamical coupled ocean-atmosphere models poorly simulate and predict equatorial Atlantic climate variability. We use multi-model numerical experiments to show that thermodynamic feedbacks excited by stochastic atmospheric perturbations can generate Atlantic Nino s.d. of B0.28±0.07 K, explaining B68±23% of the observed interannual variability. The equatorial Atlantic Ocean exhibits sporadic interannual fluctuations in zonal sea surface temperature (SST) gradients associated with westerly wind perturbations[1,2,3,4]. This dominant coupled ocean-atmosphere mode of behaviour is often considered the Atlantic equivalent of the Pacific El Nino and is referred to as the Atlantic Nino[1,2]. Driven largely by stochastic atmospheric forced heat and moisture fluxes, the Atlantic Nino is not different from a first-order autoregressive (AR(1)) process
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