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

[ACG33-03] On the complexities of ENSO’s influence on the equatorial Atlantic

*Ingo Richter¹, Tomoki Tozuka², Yu Kosaka², Shoichiro Kido¹, Ping Chang³, Hiroki Tokinaga⁴ (1.JAMSTEC Japan Agency for Marine-Earth Science and Technology, 2.University of Tokyo, 3.Texas A&M University, 4.Kyushu University)

Keywords:ENSO, Atlantic Nino, interbasin interaction, air-sea interaction

Even though El Niño-Southern Oscillation (ENSO) has a robust influence on the northern tropical Atlantic, its influence on the equatorial Atlantic is inconsistent. This is perhaps best exemplified by the fact that the extreme 1982 and 1997 El Niño events were followed by Atlantic zonal mode (AZM) events of the opposite sign. Potential reasons for this inconsistent influence are the competition of dynamic and thermodynamic effects, and the timing of ENSO decay.
Here we re-examine this problem using pre-industrial control simulations (piControl) from the Coupled Model Intercomparison Phase 6 (CMIP6). The observed correlation between boreal winter (DJF) sea-surface temperature (SST) in the Niño 3.4 region and the following summer (JJA) SSTs in the ATL3 region is close to zero, indicative of the inconsistent relation between the two. In the CMIP6, however, the relation exhibits a wide range of behaviors with correlations ranging from about -0.5 to +0.5 depending on the model. Despite this inconsistency, the influence of ENSO on surface winds over the equatorial Atlantic is rather robust, with all models showing a negative correlation between boreal spring (MAM) Niño 3.4 SST and MAM surface winds over the western equatorial Atlantic. Taking this robust ENSO influence on the Atlantic surface winds as our starting point, we examine the reasons why the consistent wind forcing does not lead to a consistent SST response in the equatorial Atlantic in CMIP6 simulations.