Interdecadal change in the relationship between boreal winter North Pacific Oscillation and Eastern Australian rainfall in the following autumn

Previous study reported that boreal winter North Pacific Oscillation (NPO) has a pronounced impact on the interannual variation of eastern Australian rainfall in the following autumn. This study reveals that impact of the winter NPO on the eastern Australian rainfall shows a marked interdecadal weakening around the late-1990s. Before the late-1990s, winter NPO leads to warm sea surface temperature anomalies (SSTAs) in the subtropical North Pacific during succedent spring via modulating surface heat fluxes. Warm SSTAs enhance atmospheric heating and lead to westerly wind anomalies over the tropical western-central Pacific via wind-evaporation-SST feedback process. The westerly wind anomalies over the tropical western-central Pacific contribute to an El Niño-like pattern in the following autumn, which further leads to decrease in the eastern Australian rainfall via modulating the tropical Walker circulation. However, after the late-1990s, winter NPO-related atmospheric anomaly shifts northward compared to that before the late-1990s. As such, the NPO-generated spring SSTAs over the subtropical North Pacific, and the westerly wind anomalies over the tropical western-central Pacific are much weaker. Hence, winter NPO cannot induce a clear El Niño-like pattern in the following autumn, and thus cannot impact eastern Australian rainfall after the late-1990s. Northward displacement of the winter NPO-related atmospheric anomalies after the late-1990s is due to northward movement of the climatological mean circulation and storm track over North Pacific. Further analysis indicates that Atlantic Multidecadal Oscillation (AMO) has a strong influence on the meridional movement of the NPO via modulating North Pacific climatological mean circulation. We suggest that AMO acts as a crucial modulator for the relation between winter NPO and subsequent autumn Australian rainfall.