[A-CG33] Multi-scale ocean-atmosphere interaction in the tropics

[ACG33-02] El Niño-Southern Oscillation has an asymmetric influence from the tropical Atlantic

★Invited Papers

*Peter van Rensch¹, Shayne McGregor^1,2, Dietmar Dommenget^1,2, Daohua Bi³, Giovanni Liguori^4,1 (1.Monash University, 2.Centre of Excellence for Climate Extremes, 3.CSIRO Environment, 4.University of Bologna)

There has been continued progress in our understanding of the Atlantic influence on the Pacific. Many studies have described early in the year warm tropical Atlantic sea surface temperature anomalies (SSTA) linked to a developing La Niña later in the year. We show using observations and models that an asymmetry exists in this relationship, where a cold Atlantic does not lead to an El Niño.

Pacemaker model experiments were used to force the observed Atlantic SST in an otherwise fully coupled atmosphere and ocean model. These experiments showed that modelled La Niña events tend of occur in unison with observed La Niña events, but this did not occur for El Niño events. In the model, warm western tropical Atlantic SSTA were associated with a tropical wide atmospheric response, which in-turn impacted western Pacific surface winds, whereas cold Atlantic SSTA was not associated with a widespread atmospheric response.

The Pacific initial state was an important factor for whether the Atlantic could impact the Pacific in the model. The Atlantic had a greater chance to force a La Niña event if the Pacific surface and subsurface had minimal anomalies earlier in the year. The model was also able to produce La Niña events independently of the Atlantic forcing, indicating the Pacific still maintains a high degree of autonomy.