Interdecadal tropical Pacific-Atlantic interaction simulated in CMIP6 models

The interaction between the tropical Pacific and Atlantic at the decadal timescale has received widespread attention. This study evaluates the simulation of the interdecadal interaction of the tropical Pacific and Atlantic in 39 Coupled Model Intercomparison Project Phase 6 (CMIP6) models. Most of CMIP6 models have a positive correlation with the observations. The high-skill models reproduce well the temporal evolution of the lead-lag correlation. However, the low-skill models cannot reproduce the observed relationship between tropical Pacific decadal variability (TPDV) and tropical Atlantic multidecadal variability (TAMV) relationship, always incorrectly simulating the observed negative correlation when TAMV leads greater than 3 years as a positive correlation. We additionally demonstrate that the intermodel spread in the TPDV-TAMV relationship when TAMV leads is primarily linked to the persistence of TPDV and the background sea surface temperature (SST) in the northern tropical Atlantic. A relatively lower background SST in the north tropical Atlantic suppresses local convection and the remote response to TAMV-related SST anomalies. Consequently, the low-level circulation anomalies in the tropical Pacific connected to TAMV in the low-skill models are not primarily dominated by the observed easterly anomalies. Our research highlights the importance of background SST in the simulation of interbasin interaction and the necessity for model selection before applying CMIP models in relevant studies.