Preprints
https://doi.org/10.5194/egusphere-2023-113
https://doi.org/10.5194/egusphere-2023-113
02 Feb 2023
 | 02 Feb 2023

How the extreme 2019–2020 Australian wildfires affected global circulation and adjustments

Fabian Senf, Bernd Heinold, Anne Kubin, Jason Müller, Roland Schrödner, and Ina Tegen

Abstract. Wildfires are a significant source of absorbing aerosols in the atmosphere. Especially extreme fires, such as those during the 2019–2020 Australian wildfire season (Black Summer fires), can have considerable large-scale effects. In this context, the climate impact of extreme wildfires not only unfolds because of the emitted carbon dioxide, but also due to smoke aerosol released as high as the stratosphere. The overall aerosol effects depend on a variety of factors, such as the amount emitted, the injection height, and the composition of the burned material, and is therefore subject to considerable uncertainty. In the present study, we address the global impact caused by the exceptionally strong and high-reaching smoke emissions from the Australian wildfires using simulations with a global aerosol-climate model. We show that the absorption of solar radiation by the black carbon contained in the emitted smoke led to a shortwave radiative forcing of more than +5 W m−2 in the southern mid-latitudes of the lower stratosphere. Subsequent adjustment processes in the stratosphere slowed down the diabatically driven meridional circulation, thus redistributing the heating perturbation on a global scale. As a result of these stratospheric adjustments, a positive temperature perturbation developed in both hemispheres leading to additional longwave radiation emitted back to space. According to the model results, this adjustment occurred in the stratosphere within the first two months after the event. At the top of atmosphere (TOA), the net effective radiative forcing (ERF) in the southern hemisphere was initially dominated by the instantaneous positive radiative forcing of about +0.5 W m−2, for which the positive sign resulted mainly from the presence of clouds above the Southern Ocean. The longwave adjustments led to a compensation of the initially net positive TOA ERF, which is seen in the southern hemisphere, the tropics and the northern mid-latitudes. The changes in the lower stratosphere also affected the upper troposphere through a thermodynamic downward coupling mechanism in the model. Subsequently, increased temperatures were also obtained in the upper troposphere, causing a decrease in relative humidity, cirrus amount, and the ice water path. As a result, surface precipitation also decreased, which was accompanied by a weakening of the tropospheric circulation due to the given energetic constraints. In general, it appears that the radiative effects of smoke from single extreme wildfire events can lead to global impacts that affect the interplay of tropospheric and stratospheric cycles in complex ways. This emphasizes that future changes in extreme wildfires need to be included in projections of aerosol radiative forcing.

Journal article(s) based on this preprint

11 Aug 2023
How the extreme 2019–2020 Australian wildfires affected global circulation and adjustments
Fabian Senf, Bernd Heinold, Anne Kubin, Jason Müller, Roland Schrödner, and Ina Tegen
Atmos. Chem. Phys., 23, 8939–8958, https://doi.org/10.5194/acp-23-8939-2023,https://doi.org/10.5194/acp-23-8939-2023, 2023
Short summary

Fabian Senf et al.

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Review of Senf et al.', Anonymous Referee #1, 08 Mar 2023
  • RC2: 'Comment on egusphere-2023-113', Anonymous Referee #2, 26 Mar 2023

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Review of Senf et al.', Anonymous Referee #1, 08 Mar 2023
  • RC2: 'Comment on egusphere-2023-113', Anonymous Referee #2, 26 Mar 2023

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
AR by Fabian Senf on behalf of the Authors (22 May 2023)  Author's response   Manuscript 
ED: Referee Nomination & Report Request started (24 May 2023) by Farahnaz Khosrawi
RR by Anonymous Referee #2 (14 Jun 2023)
EF by Polina Shvedko (25 May 2023)  Author's tracked changes 
ED: Publish subject to minor revisions (review by editor) (16 Jun 2023) by Farahnaz Khosrawi
AR by Fabian Senf on behalf of the Authors (26 Jun 2023)  Author's response   Author's tracked changes   Manuscript 
ED: Publish as is (27 Jun 2023) by Farahnaz Khosrawi
AR by Fabian Senf on behalf of the Authors (06 Jul 2023)

Journal article(s) based on this preprint

11 Aug 2023
How the extreme 2019–2020 Australian wildfires affected global circulation and adjustments
Fabian Senf, Bernd Heinold, Anne Kubin, Jason Müller, Roland Schrödner, and Ina Tegen
Atmos. Chem. Phys., 23, 8939–8958, https://doi.org/10.5194/acp-23-8939-2023,https://doi.org/10.5194/acp-23-8939-2023, 2023
Short summary

Fabian Senf et al.

Data sets

Dataset associated with Senf et al. (2023): "How the extreme 2019-2020 Australian wildfire affected global circulation and adjustments" Fabian Senf, Bernd Heinold, Anne Kubin, Jason Müller, Roland Schrödner, and Ina Tegen https://doi.org/10.5281/zenodo.7568466

Jupyter Notebooks for Plotting and Analysis of the "Circulation Responses for WiFi-AUS" study, Submission Release Fabian Senf https://doi.org/10.5281/zenodo.7575809

Fabian Senf et al.

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Short summary
Wildfire smoke is a significant source of airborne atmospheric particles that can absorb sun light. Especially extreme fires, such as those during the 2019–2020 Australian wildfire season (Black Summer fires), can considerably affect our climate system. In the present study, we investigate the various effects of Australian smoke using a global climate model to clarify how the Earth's atmosphere including its circulation systems adjusted to the extraordinary amount of Australian smoke.