The North Pacific Meridional Mode (PMM) is the leading atmosphere-ocean coupling pattern over the subtropical northeastern Pacific. In this study, we reveal that the impact of the PMM in boreal spring on the following-winter El Niño and Southern Oscillation (ENSO) enhanced significantly after the mid-1980s according to multiple observational and reanalysis datasets. After the mid-1980s, the spring PMM related sea surface temperature (SST) and atmospheric anomalies over the subtropical northeastern Pacific could propagate southwestward to the tropical central Pacific via wind-evaporation-SST (WES) feedback. The tropical SST and atmospheric anomalies further develop to an ENSO-like pattern via a positive air-sea interaction. By contrast, before the mid-1980s, SST and atmospheric anomalies over the subtropical northeastern Pacific in association with the PMM cannot extend to the deep tropics. Therefore, the spring PMM has a weak contribution to the occurrence of ENSO. Variation of the spring PMM-winter ENSO relation is related to changes in the background flow. The strong mean trade winds after the mid-1980s lead to an increase in the air-sea coupling over the subtropical northeastern Pacific. Thus, the spring PMM-related SST anomalies can propagate southwestward to the tropical central Pacific and exert impacts on the succedent winter ENSO. In addition, the southward shifted Inter-tropical convergence zone after the mid-1980s also favors the southward extension of the PMM-related atmospheric anomalies to the deep tropics and contributes to a stronger spring PMM-winter ENSO connection. The interdecadal variation and its formation mechanism of the spring PMM-winter ENSO relationship appear in both the observations and a long historical simulation generated by the CIESM model.

ENSO, Pacific Meridional Mode, Air-sea interaction, Interdecadal variation