2019-2020 Australian bushfire smoke, multi-year La Niña, and implications for the Interdecadal Pacific Oscillation (IPO)

The onset of a La Niña event in 2020, with a major contribution from the huge amounts of smoke produced by the disastrous 2019–2020 Australian bushfires, resulted in that event persisting over the next several years with significant impacts worldwide. Here, we attempt to understand the processes and mechanisms related to the wildfire smoke that could have sustained this multi-year high-impact event by analyzing initialized Earth system predictions with E3SMv2 and CESM2 with and without the effects of the Australian bushfire smoke. We hypothesize that Bjerknes feedback sustains the La Niña conditions through an intensified anomalous Walker Circulation that connects strengthened precipitation and ascent in the western Pacific with anomalous subsidence, an invigorated South Pacific High, stronger Trades, and cooler SSTs across the tropical Pacific. Some ensemble members transition to El Niño after 2 years, driven by the development of a positive North Pacific Meridional Mode (NPMM) near Hawaii. Coupled processes in the off-equatorial western Pacific Ocean indicate a connection to the negative phase of the Interdecadal Pacific Oscillation with implications for understanding and predicting interannual and decadal Earth system fluctuations.