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

Authors

Senf,  Fabian
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Heinold,  Bernd
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Kubin,  Anne
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Müller,  Jason
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Schrödner,  Roland
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Tegen,  Ina
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

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Citation

Senf, F., Heinold, B., Kubin, A., Müller, J., Schrödner, R., Tegen, I. (2023): How the extreme 2019–2020 Australian wildfires affected global circulation and adjustments, XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG) (Berlin 2023).
https://doi.org/10.57757/IUGG23-0795


Cite as: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5016691
Abstract
The uncertain climate impact of extreme wildfires not only unfolds because of the emitted carbon dioxide, but also due to smoke aerosol. 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. 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.