21.08.2023: Ocean Circulation and Climate Dynamics Colloquium

When?  Monday, 21 August 2023 at 11 am
Where?    Hörsaal, Düsternbrooker Weg 20

Abstract:

Even though El Niño-Southern Oscillation (ENSO) is well known to have global impact, 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 delayed effect of off-equatorial Rossby waves forced by wind stress curl north of the equator.
Here we re-examine this problem using pre-industrial control simulations (piControl) from the Coupled Model Intercomparison Phase 6 (CMIP6). While 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, the models exhibit a wide range of behaviors with correlations ranging from about -0.5 to +0.5. 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 DJF Niño 3.4 SST and boreal spring (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.

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