Contrasting Responses of Smoke Dispersion and Fire Emissions to Aerosol-Radiation Interaction during the Largest Australian Wildfires in 2019-2020.

The record-breaking 2019-2020 Australian wildfires have been primarily linked to climate change and its internal variability. However, the meteorological feedback mechanisms affecting smoke dispersion and wildfire emissions on a synoptic scale remain unclear. This study focused on the largest wildfires occurring between December 25, 2019 and January 10, 2020, under the enhanced subtropical high, when the double peak in wildfire evolution was favored by sustained low humidity and two synchronous increases in temperature and wind. Based on the coupled atmospheric chemical transport model, we revealed an abnormal downdraft and a lowered planetary boundary layer over southeastern Australia, caused by the radiative cooling effects (exceeding -100 W m at surface) of carbonaceous aerosols (CAs) from wildfires. These changes hindered the smoke dispersion and increased the PM concentration by ∼27.8%. By contrast, the low-level anomalous cyclonic circulation induced by CAs brought more water vapor toward the fire zone. This, combined with surface cooling and low wind speeds, suppressed wildfire emissions, thereby reducing PM concentration by ∼11.6%. These findings highlight the critical role of aerosol-radiation interaction in wildfire behavior.