Short and long-term stratospheric impact of smoke from the 2019/2020 Australian wildfires

Abstract. In the end of December 2019 and beginning of 2020, massive firestorms in Australia formed pyrocumulonimbus clouds (PyroCb) that acted like enormous smokestacks, pumping smoke to the upper troposphere and stratosphere. We study the smoke with data from four satellite-based sensors: the aerosol observation platforms CALIOP, OMPS-LP, and OMPS-NM, and water vapor retrievals from MLS. Smoke was lifted to the upper troposphere and stratosphere during two events and spread almost exclusively within the extratropics. Smoke from the 1st event, starting Dec 29, was injected directly into the stratosphere by pyrocumulonimbus clouds causing a rapid initial increase in AOD. CALIOP identifies a rapid decline in this stratospheric smoke (half-life: 10 days), not captured in previous studies of the Australian fires, indicating photochemical processing of organic aerosol. This decay rate is in line with model predictions of mid-tropospheric organic aerosol loss by photolytic removal and is similar to our estimates of decay rates after the North American fires in Aug 2017. Smoke from the 2nd event, Jan 4, appeared in the stratosphere after more than one week of transport in the troposphere, forming a second peak in the aerosol load. The AOD from the 2nd event fires decreased more slowly than the AOD from the 1st event, likely due to chemical processing of this smoke in the humid troposphere during its slower transport to the stratosphere. Together these injections gave a major elevation of the aerosol load during almost one year.