Striking repercussions of the Australian "Black Summer" bushfires on the stratospheric composition and dynamical circulation

Abstract : Wildfire-driven pyro-convection (PyroCb) is capable of lofting combustion products into the stratosphere, polluting it with smoke aerosols at hemispheric and yearly scales. This realization has emerged after the record-breaking British Columbia PyroCb event in August 2017 that approached moderate volcanic eruptions in terms of stratospheric aerosol load perturbation. The Australian “Black Summer” bushfires in 2019/20 have surpassed the previous record by a factor of 3 and rivaled the strongest volcanic eruptions in the XXI century. Here we exploit a synergy of various satellite observations, ECMWF meteorological analysis and radiative transfer modeling to quantify the perturbation of stratospheric particulate and gaseous composition, dynamical circulation and radiative balance caused by the Australian New Year’s PyroCb outbreak. One of the most striking repercussions of this event was the generation of several persistent anticyclonic vortices that provided confinement to the PyroCb plumes and preserved them from rapid dilution in the environment. The most intense vortex measured 1000 km in diameter, persisted in the stratosphere for over 13 weeks and lifted a confined bubble of combustion gases, aerosols and moisture to 35 km altitude. It was accompanied by a synoptic-scale ozone hole with the total column reduction by about 30%. The startling consequences of the Australian event provide new insights into climate-altering potential of the wildfires, that have increased in frequency and strength over the recent years.