Radiative impacts of the Australian bushfires 2019–2020 – Part 1: Large-scale radiative forcing
<p>As a consequence of extreme heat and drought, record-breaking wildfires developed and ravaged south-eastern Australia during the fire season 2019–2020. The fire strength reached its paroxysmal phase at the turn of the year 2019–2020. During this phase, pyrocumulonimbus clouds (pyroCb) devel...
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2022-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/22/9299/2022/acp-22-9299-2022.pdf |
| _version_ | 1811295945064710144 |
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| author | P. Sellitto P. Sellitto R. Belhadji C. Kloss B. Legras |
| author_facet | P. Sellitto P. Sellitto R. Belhadji C. Kloss B. Legras |
| author_sort | P. Sellitto |
| collection | DOAJ |
| description | <p>As a consequence of extreme heat and drought,
record-breaking wildfires developed and ravaged south-eastern Australia
during the fire season 2019–2020. The fire strength reached its paroxysmal
phase at the turn of the year 2019–2020. During this phase, pyrocumulonimbus clouds (pyroCb) developed and injected biomass burning aerosols and gases into the
upper troposphere and lower stratosphere (UTLS). The UTLS aerosol layer was
massively perturbed by these fires, with aerosol extinction increased by a
factor of 3 in the visible spectral range in the Southern Hemisphere, with
respect to a background atmosphere, and stratospheric aerosol optical depth
reaching values as large as 0.015 in February 2020. Using the best available
description of this event by observations, we estimate the radiative forcing
(RF) of such perturbations of the Southern Hemispheric aerosol layer. We use
offline radiative transfer modelling driven by observed information of the
aerosol extinction perturbation and its spectral variability obtained from
limb satellite measurements. Based on hypotheses on the absorptivity and the
angular scattering properties of the aerosol layer, the regional (at three
latitude bands in the Southern Hemisphere) clear-sky TOA (top-of-atmosphere)
RF is found varying from small positive values to relatively large negative
values (up to <span class="inline-formula">−2.0</span> W m<span class="inline-formula"><sup>−2</sup></span>), and the regional clear-sky surface RF is
found to be consistently negative and reaching large values (up to <span class="inline-formula">−4.5</span> W m<span class="inline-formula"><sup>−2</sup></span>). We argue that clear-sky positive values are unlikely for this
event, if the ageing/mixing of the biomass burning plume is mirrored by the
evolution of its optical properties. Our best estimate for the area-weighted
global-equivalent clear-sky RF is <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">0.35</mn><mo>±</mo><mn mathvariant="normal">0.21</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="64pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="0e7f3e36ab8722a4405fca577758aa6a"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-9299-2022-ie00001.svg" width="64pt" height="10pt" src="acp-22-9299-2022-ie00001.png"/></svg:svg></span></span> (TOA RF) and
<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">0.94</mn><mo>±</mo><mn mathvariant="normal">0.26</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="64pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="bd501a800047bfc59def03f942a4842d"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-9299-2022-ie00002.svg" width="64pt" height="10pt" src="acp-22-9299-2022-ie00002.png"/></svg:svg></span></span> W m<span class="inline-formula"><sup>−2</sup></span> (surface RF), thus the strongest documented for
a fire event and of comparable magnitude with the strongest volcanic
eruptions of the post-Pinatubo era. The surplus of RF at the surface, with
respect to TOA, is due to absorption within the plume that has contributed
to the generation of ascending smoke vortices in the stratosphere. Highly
reflective underlying surfaces, like clouds, can nevertheless swap negative
to positive TOA RF, with global average RF as high as <span class="inline-formula">+1.0</span> W m<span class="inline-formula"><sup>−2</sup></span>
assuming highly absorbing particles.</p> |
| first_indexed | 2024-04-13T05:41:04Z |
| format | Article |
| id | doaj.art-60535e39fd7043d0a30a6684fb8c25cd |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-04-13T05:41:04Z |
| publishDate | 2022-07-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-60535e39fd7043d0a30a6684fb8c25cd2022-12-22T03:00:06ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242022-07-01229299931110.5194/acp-22-9299-2022Radiative impacts of the Australian bushfires 2019–2020 – Part 1: Large-scale radiative forcingP. Sellitto0P. Sellitto1R. Belhadji2C. Kloss3B. Legras4Univ. Paris-Est Créteil and Université de Paris Cité, CNRS, Laboratoire Interuniversitaire des Systèmes Atmosphériques, Institut Pierre Simon Laplace, Créteil, FranceIstituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo, Catania, ItalyUniv. Paris-Est Créteil and Université de Paris Cité, CNRS, Laboratoire Interuniversitaire des Systèmes Atmosphériques, Institut Pierre Simon Laplace, Créteil, FranceLaboratoire de Physique de l'Environnement et de l'Espace, Orléans, FranceLaboratoire de Météorologie Dynamique, UMR CNRS 8539, École Normale Supérieure, PSL Research University, École Polytechnique, Sorbonne Universités, École des Ponts PARISTECH, Institut Pierre Simon Laplace, Paris, France<p>As a consequence of extreme heat and drought, record-breaking wildfires developed and ravaged south-eastern Australia during the fire season 2019–2020. The fire strength reached its paroxysmal phase at the turn of the year 2019–2020. During this phase, pyrocumulonimbus clouds (pyroCb) developed and injected biomass burning aerosols and gases into the upper troposphere and lower stratosphere (UTLS). The UTLS aerosol layer was massively perturbed by these fires, with aerosol extinction increased by a factor of 3 in the visible spectral range in the Southern Hemisphere, with respect to a background atmosphere, and stratospheric aerosol optical depth reaching values as large as 0.015 in February 2020. Using the best available description of this event by observations, we estimate the radiative forcing (RF) of such perturbations of the Southern Hemispheric aerosol layer. We use offline radiative transfer modelling driven by observed information of the aerosol extinction perturbation and its spectral variability obtained from limb satellite measurements. Based on hypotheses on the absorptivity and the angular scattering properties of the aerosol layer, the regional (at three latitude bands in the Southern Hemisphere) clear-sky TOA (top-of-atmosphere) RF is found varying from small positive values to relatively large negative values (up to <span class="inline-formula">−2.0</span> W m<span class="inline-formula"><sup>−2</sup></span>), and the regional clear-sky surface RF is found to be consistently negative and reaching large values (up to <span class="inline-formula">−4.5</span> W m<span class="inline-formula"><sup>−2</sup></span>). We argue that clear-sky positive values are unlikely for this event, if the ageing/mixing of the biomass burning plume is mirrored by the evolution of its optical properties. Our best estimate for the area-weighted global-equivalent clear-sky RF is <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">0.35</mn><mo>±</mo><mn mathvariant="normal">0.21</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="64pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="0e7f3e36ab8722a4405fca577758aa6a"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-9299-2022-ie00001.svg" width="64pt" height="10pt" src="acp-22-9299-2022-ie00001.png"/></svg:svg></span></span> (TOA RF) and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">0.94</mn><mo>±</mo><mn mathvariant="normal">0.26</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="64pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="bd501a800047bfc59def03f942a4842d"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-9299-2022-ie00002.svg" width="64pt" height="10pt" src="acp-22-9299-2022-ie00002.png"/></svg:svg></span></span> W m<span class="inline-formula"><sup>−2</sup></span> (surface RF), thus the strongest documented for a fire event and of comparable magnitude with the strongest volcanic eruptions of the post-Pinatubo era. The surplus of RF at the surface, with respect to TOA, is due to absorption within the plume that has contributed to the generation of ascending smoke vortices in the stratosphere. Highly reflective underlying surfaces, like clouds, can nevertheless swap negative to positive TOA RF, with global average RF as high as <span class="inline-formula">+1.0</span> W m<span class="inline-formula"><sup>−2</sup></span> assuming highly absorbing particles.</p>https://acp.copernicus.org/articles/22/9299/2022/acp-22-9299-2022.pdf |
| spellingShingle | P. Sellitto P. Sellitto R. Belhadji C. Kloss B. Legras Radiative impacts of the Australian bushfires 2019–2020 – Part 1: Large-scale radiative forcing Atmospheric Chemistry and Physics |
| title | Radiative impacts of the Australian bushfires 2019–2020 – Part 1: Large-scale radiative forcing |
| title_full | Radiative impacts of the Australian bushfires 2019–2020 – Part 1: Large-scale radiative forcing |
| title_fullStr | Radiative impacts of the Australian bushfires 2019–2020 – Part 1: Large-scale radiative forcing |
| title_full_unstemmed | Radiative impacts of the Australian bushfires 2019–2020 – Part 1: Large-scale radiative forcing |
| title_short | Radiative impacts of the Australian bushfires 2019–2020 – Part 1: Large-scale radiative forcing |
| title_sort | radiative impacts of the australian bushfires 2019 2020 part 1 large scale radiative forcing |
| url | https://acp.copernicus.org/articles/22/9299/2022/acp-22-9299-2022.pdf |
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