Oceanic forcing of the interhemispheric SST dipole associated with the Atlantic Multidecadal Oscillation

Abstract

In this study, the interhemispheric sea surface temperature (SST) signature of the Atlantic Multidecadal Oscillation (AMO) is analyzed and compared between observations and slab ocean model (SOM) simulations. Observational analysis suggests a robust interhemispheric SST dipole across the Atlantic associated with the AMO, manifested by a strong inverse relationship between the AMO and subpolar South Atlantic decadal SST anomalies. None of the SOMs analyzed could reproduce the observed interhemispheric dipole of the AMO; instead, they consistently simulate an interhemispheric coherent SST pattern. In the SOMs, the North Atlantic decadal SST anomalies synchronize the variations of South Atlantic SST through a cross-hemispheric atmosphere teleconnection and thermodynamic processes. This discrepancy between the SOM simulations and the observation is possibly due to deficiencies in representing ocean dynamical processes. Further analyses of the fully coupled versions of the SOMs suggest that the observed interhemispheric dipole of the AMO can be reproduced only by including ocean dynamics related to the Atlantic meridional overturning circulation. Our findings highlight that the ocean dynamics play a non-negligible role and should be taken into consideration in better understanding the observed feature of the AMO.