Two regimes of inter-basin interactions between the Atlantic and Pacific Oceans on interannual timescales

Understanding the inter-basin interactions between the Atlantic and Pacific Oceans is of great concern due to their substantial global climatic implications. By analyzing observational reanalysis datasets (1948–2020), we found that there are two regimes in Atlantic–Pacific inter-basin interactions: (1) the Pacific-driven regime, and (2) the Atlantic-driven regime. In the Pacific-driven regime before the mid-1980s, the El Niño–Southern Oscillation (ENSO) in winter effectively drives the primary mode of sea surface temperature anomaly (SSTA) in the tropical Atlantic (i.e., North Tropical Atlantic (NTA) mode) in the following spring. The NTA mode has a meridional contrast of SSTA along the Atlantic Intertropical Convergence Zone, similar to the Atlantic Meridional Mode. Whereas, in the Atlantic-driven regime after the mid-1980s, the ENSO effect on the NTA becomes remarkably weaker, so that the NTA mode is featured with a SSTA monopole. Notably, the NTA mode without the meridional contrast of SSTA is capable of modulating an ENSO event with a lag. Our analyses of the latest climate models participating in the Coupled Model Intercomparison Project (CMIP) phases 6 support the hypothesis that the two regimes engendered by the Atlantic–Pacific inter-basin interactions are likely due to natural variability.