The material life cycle of Koobor: separating coherent organization from potential-vorticity evolution in a wildfire-generated stratospheric vortex

Abstract

Pyro-cumulonimbus convection associated with extreme wildfires can generate long-lived stratospheric vortices, yet their material coherence and life cycle remain poorly characterized. We apply geodesic vortex detection to winds from reanalysis to identify objectively defined (observer-independent) material boundaries of \emph{Koobor}, generated by the 2019--2020 Australian bushfires. These boundaries are closed material curves that undergo uniform finite-time tangential stretching and resist filamentation. We reconstruct their evolution across isentropic levels. Material coherence develops upward from 590~K, reaches maximum persistence at 690~K, and becomes progressively shorter-lived at higher levels. At 690~K, the reconstructed birth-to-death interval is approximately 40~days, while overlapping detections across levels define a nearly 60-day envelope. Analysis of potential vorticity (PV) within and around these material boundaries reveals a distinct dynamical evolution: the material boundary forms before strong PV isolation develops, a compact PV core emerges during the mature phase, and PV isolation weakens as material coherence approaches its demise. Strong PV isolation is concentrated at intermediate levels, whereas at 850~K material coherence occurs without a comparably well-defined PV core. These results provide an objective material description of the birth, vertical development, and decay of a wildfire-generated stratospheric vortex and show that material organization precedes the development of its strongest PV signature, which subsequently intensifies and weakens over the lifetime of the coherent vortex.

arXiv commentImproved version of an earlier manuscript submitted to NPG, with a substantially revised treatment of material coherence and the addition of potential-vorticity analysis. The revised manuscript will be submitted to JGR: Atmospheres. Comments welcome!