Wildfire Smoke Highlights Troposphere-to-Stratosphere Pathway

Following the 2020 wildfires in Australia, an extremely large amount of smoke entered the stratosphere and was dispersed throughout the southern hemisphere stratosphere. However, the pathway and entry point of the smoke into the stratosphere and the underlying mechanism remained unclear. Here, Lagrangian trajectory analysis is used to examine the flow downstream of the fires in the south Pacific, where the smoke was detected. We find that tropical cyclone Sarai merged with an extratropical cyclone to form a troposphere-wide cyclonic system, with a deep potential vorticity cutoff above it. The smoke first traveled in the isentropic layer between 340 and 350 °K. Having reached the cyclone, the smoke circulated and entered the stratosphere through a dip in the tropopause height within the cutoff. The cyclone described in this case study is not uncommon in these regions, possibly underlining the importance of this mechanism for troposphere-to-stratosphere exchange.