Material coherence and life cycle of a wildfire-generated stratospheric vortex

Abstract. Pyro-cumulonimbus convection associated with extreme wildfires can generate longlived vortical structures in the stratosphere. These structures have been described as coherent, yet a rigorous material characterization has remained lacking. Here we provide such a characterization by applying geodesic vortex detection to reanalysis winds during the 2019–2020 Australian bushfires.

We identify a coherent Lagrangian vortex, dubbed Koobor, whose boundary is given by materially coherent loops exhibiting nearly uniform stretching and strong resistance to filamentation over finite time intervals of up to 40 days. The detected vortex extends across multiple isentropic levels, revealing a vertically organized evolution with delayed onset and reduced persistence at higher levels.

Taken together across isentropic levels, the reconstructed life cycle indicates that Koobor maintained quasi-material coherence for nearly 60 days from its first detection, through a sequence of overlapping materially coherent boundaries rather than a single boundary advected over the entire period.

Our results establish a material framework for wildfire-induced stratospheric vortices and provide a dynamically consistent description of their life cycle, from formation to decay