Self-confinement of wildfire smoke within long-lived vortices rising in the stratosphere

Abstract

International audienceThe 2019-2020 Australian wildfires have produced a striking phenomenon in the stratosphere: an ascending disc of smoke contained within an anticyclonic vortex that persisted 3 months, travelled 66000 km and rose from 16 to 36 km. We analyse this exceptional structures and several of its companions with CALIOP data and the ERA5 reanalysis demonstrating its analogy with ellipsoidal free solutions of the quasi-geostrophic equation. A main difference is that here the vortex is maintained and rises due to the heating by the absorbing smoke. In the ERA5, where the wildfire smoke is missing, this forcing is exerted by the assimilation of spaceborne temperature profiles that produces an assimilation increment compensating the fast decay of the free solution. Based on these observations, we discuss the theoretical basis for the self-organisation and the stability of the smoke vortex. We show evidences that similar events, albeit of lesser magnitude, have already occurred, in particular during the Australian 2009 wildfire and the Canadian 2017 widlfire