The Tropical Atlantic's Asymmetric Impact on the El Niño-Southern Oscillation

Using observations and Atlantic forced coupled model simulations, we show evidence for an asymmetry in the link between beginning of year tropical Atlantic sea surface temperature anomalies (SSTAs) and end of the year El Niño-Southern Oscillation events. We find a greater tendency for warm Atlantic SSTAs to lead to a La Niña than for cold anomalies to lead to El Niño. The model experiments showed that the Atlantic had a greater chance to force the tropical Pacific if the Pacific was initially in a neutral state. In the model, a warm Atlantic from March–May was able to produce an atmospheric response leading to easterly wind anomalies in the western Pacific. This in turn induces a subsurface oceanic response, leading to La Niña at the end of the year. The atmospheric response does not occur for a cold Atlantic, leading to no impacts in the Pacific.