The 2019/20 Australian wildfires generated a persistent smoke-charged vortex rising up to 35\u2009km altitude

Sergey Khaykin,Adam Bourassa,Bernard Legras,Florent Tencé,Sophie Godin-Beekmann,Daniel Zawada,Slimane Bekki,Landon Rieger,Lars Isaksen,Silvia Bucci,Julien Jumelet,Pasquale Sellitto

doi:10.1038/s43247-020-00022-5

Abstract

The Australian bushfires around the turn of the year 2020 generated an unprecedented perturbation of stratospheric composition, dynamical circulation and radiative balance. Here we show from satellite observations that the resulting planetary-scale blocking of solar radiation by the smoke is larger than any previously documented wildfires and of the same order as the radiative forcing produced by moderate volcanic eruptions. A striking effect of the solar heating of an intense smoke patch was the generation of a self-maintained anticyclonic vortex measuring 1000 km in diameter and featuring its own ozone hole. The highly stable vortex persisted in the stratosphere for over 13 weeks, travelled 66,000 km and lifted a confined bubble of smoke and moisture to 35 km altitude. Its evolution was tracked by several satellite-based sensors and was successfully resolved by the European Centre for Medium-Range Weather Forecasts operational system, primarily based on satellite data. Because wildfires are expected to increase in frequency and strength in a changing climate, we suggest that extraordinary events of this type may contribute significantly to the global stratospheric composition in the coming decades.

Highlights

The Australian bushfires around the turn of the year 2020 generated an unprecedented perturbation of stratospheric composition, dynamical circulation and radiative balance
Another PyroCb outbreak with stratospheric impact, less vigorous, took place on 4 January 2020 and on 7 January, the horizontal extent of the stratospheric smoke cloud peaked at 6.1 million km[2] (Fig. 1b) extending over much of the Southern midlatitudes (Fig. 2 and Supplementary Fig. 4c)
Three months after the PyroCb event, the stratospheric aerosol optical depth (SAOD) perturbation has remained at the volcanic levels, gradually decreasing with a rate similar to the decay of stratospheric aerosol produced by moderate volcanic eruptions

Summary

Introduction

The Australian bushfires around the turn of the year 2020 generated an unprecedented perturbation of stratospheric composition, dynamical circulation and radiative balance. Pyro-cumulonimbus (pyroCb) clouds from that event caused stratospheric perturbations an order of magnitude larger than the previous benchmarks of extreme pyroCb activity and approached the effect of moderate volcanic eruption[1,2]. We use various satellite observations to quantify the magnitude of hemispheric-scale perturbation of stratospheric gaseous compounds and aerosol loading caused by these wildfires. Using the operational forecasting system of the European Centre for Medium-Range Weather Forecasts (ECMWF)[6] we show that the solar heating of an intense smoke patch has led to generation of a quasi-ellipsoidal anticyclonic vortex which lofted a confined bubble of carbonaceous aerosols and water vapour up to 35 km altitude in about 3 months

Methods

Results

Discussion

Conclusion