Australian PyroCb Smoke Generates Synoptic‐Scale Stratospheric Anticyclones

Fires in southeastern Australia produced at least 18 pyrocumulonimbus (pyroCb) between 29 December 2019 and 4 January 2020. The largest plumes from this event exhibited several previously undocumented phenomena in the stratosphere. These include (i) the generation of potential vorticity and anticyclonic circulations from absorptive aerosol heating, (ii) the formation of a vertical temperature anomaly dipole, (iii) the rapid ascent from the lowermost stratosphere (15–16 km) to altitudes above 31 km in less than 2 months, (iv) an unprecedented abundance of H2O and CO in the stratosphere, and (v) the displacement of background O3 and N2O from rapid ascent of air from the troposphere and lower stratosphere. Each of these phenomena is traced back to a 5‐day‐old stratospheric plume composed of a massive amount of aerosol and biomass burning gases from a pyroCb outbreak. Until now, there has been no documented evidence that pyroCb plumes can affect stratospheric winds. Plain Language Summary The 2019–2020 bushfire season in Australia has been referred to as the Black Summer by the Australian government due to the extreme amount of destruction it caused. One particularly intense period during this season was between 29 December 2019 and 4 January 2020, when an outbreak of huge thunderstorms fueled by very intense bushfires in southeast Australia emitted unprecedented amounts of smoke to heights 16 km above the surface. Multiple smoke plumes traveled around the Southern Hemisphere over the next few months. One plume (about 1,000 km across and 5 km thick) with very high smoke concentration traveled east from Australia to South America by late January, then reversed course, and completely circled the globe westward over the next few weeks. This plume showed several unusual characteristics, such as excessive lofting from 15 to 30 km due to smoke‐induced heating, low ozone, and high nitrous oxide concentrations typical of air at much lower altitudes and winds rotating around the plume at about 15 m s−1. Some of the smaller smoke plumes also showed significant rising and rotation. This is the first evidence of smoke causing changes to winds in the stratosphere and opens up a whole new vein of scientific research. Key Points Pyrocumulonimbus plumes diabatically heated the local stratosphere, driving rapid ascent from the tropopause to heights above 31 km A global model shows that these aerosol perturbations generated potential vorticity and anticyclonic circulations, las