AMO and PDO modulate the multidecadal variability of WACE

Since global warming, the Warm Arctic-Cold Eurasia (WACE) has experienced significant interdecadal variabilities, and its interdecadal variability has increased significantly after Arctic amplification. Temperature changes over Barents-Kara Seas region play a leading role in the interdecadal variability of WACE. Before Arctic amplification, the circulation influencing WACE was primarily characterized by the meridional circulation of the Arctic-Eurasian Dipole. After Arctic amplification, however, the circulation is mainly represented by the north-south Rossby wave trains over the Eurasian continent. Before Arctic amplification, the Atlantic Multidecadal Oscillation (AMO) and the Pacific Decadal Oscillation (PDO) changed in phase, stimulating the eastward propagation of Rossby wave trains along the mid-latitudes. The PDO-induced Arctic-Eurasian Dipole circulation played a leading role over Eurasian, while the AMO weakened the PDO signal in the key North Atlantic and Arctic regions. While after Arctic amplification, the AMO and PDO change in an out-of-phase relationship, with the eastward propagation of Rossby wave trains still occurring along the mid-latitudes. In this phase, the south-north Rossby wave trains excited by the AMO dominate over Eurasian, with the PDO weakening the AMO signal in the North Atlantic and enhancing the AMO signal in the critical Arctic region. Since the interdecadal variability of WACE is primarily driven by temperature changes in the key regions of Arctic, both the PDO and AMO play crucial roles in modulating the interdecadal changes in WACE before and after Arctic amplification. The two exhibit an antagonistic relationship before Arctic amplification, while their relationship becomes primarily synergistic after amplification.