Abstract
Abstract. The two most intense wildfires of the last decade that took place in Canada in 2017 and Australia in 2019–2020 were followed by large injections of smoke into the stratosphere due to pyro-convection. After the Australian event, Khaykin et al. (2020) and Kablick et al. (2020) discovered that part of this smoke self-organized as anticyclonic confined vortices that rose in the mid-latitude stratosphere up to 35 km. Based on Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) observations and the ERA5 reanalysis, this new study analyses the Canadian case and finds, similarly, that a large plume had penetrated the stratosphere by 12–13 August 2017 and then became trapped within a mesoscale anticyclonic structure that travelled across the Atlantic. It then broke into three offspring that could be followed until mid-October, performing three round-the-world journeys and rising up to 23 km. We analyse the dynamical structure of the vortices produced by these two wildfires and demonstrate how the assimilation of the real temperature and ozone data from instruments measuring the signature of the vortices explains the appearance and maintenance of the vortices in the constructed dynamical fields. We propose that these vortices can be seen as bubbles of small, almost vanishing, potential vorticity and smoke carried vertically across the stratification from the troposphere inside the middle stratosphere by their internal heating, against the descending flux of the Brewer–Dobson circulation.
Highlights
A spectacular consequence of large summer wildfires in mid-latitude forests is the generation of pyro-cumulonimbus (PyroCb) that can reach the lower stratosphere during extreme events (Fromm et al, 2010)
The smoke bubbles were attributed to vortices based on the ERA5 reanalysis which were available throughout their life cycles
The western component could be followed until 4 September, accompanied by patches seen by Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP); it remained below 460 K and could not be linked to any structure seen from CALIOP after 15 September with any certainty
Summary
A spectacular consequence of large summer wildfires in mid-latitude forests is the generation of pyro-cumulonimbus (PyroCb) that can reach the lower stratosphere during extreme events (Fromm et al, 2010). A stratospheric rise of up to 30 K d−1 in potential temperature was diagnosed based on satellite observations by Khaykin et al (2018), and a compact smoke cloud at 19 km over the Haute-Provence Observatory, southern France, on 29 August 2017 was reported in the same study. Another goal of this work is to complement Khaykin et al (2020) by expanding their diagnostics and interpretations on the 2020 case. This paper is structured as follows: Sect. 2 describes the data and methods used in this work; Sect. 3 describes the new vortices found after the 2017 Canadian fire and their evolution, including a detailed discussion of previous results; Sect. 4 describes the structure of the vortices based on the 2017 Canadian case and the 2020 Australian case; and Sect, 5 offers conclusions
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