Significant Effective Radiative Forcing of Stratospheric Wildfire Smoke

Liu, Cheng‐Cheng; Portmann, R. W.; Liu, Shang; Rosenlof, Karen H.; Peng, Yifeng; Yu, Pengfei

doi:10.1029/2022gl100175

Cited by 7 publications

(10 citation statements)

References 61 publications

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“…2a) because the absorbed flux in the middle atmosphere more than offsets the reduction of shortwave fluxes at the surface. In relative terms, this reduction appears to be much smaller than reported elsewhere in literature (Hirsch and Koren, 2021;Yu et al, 2021;Liu et al, 2022), however, we will show in the next section that the presence of clouds is of major importance for the quantification of surface and TOA forcing of the Australian smoke event. The negative longwave TOA flux compensates the shortwave TOA forcing such that in the net, the radiative forcing cannot be differentiated from zero with confidence (Fig.…”

Section: Indications Of Global Adjustments To Smoke-radiation Interac...mentioning

confidence: 58%

“…Once there, the fire aerosol had a significantly longer lifetime compared to smoke remaining in the lower troposphere, allowing it to disperse throughout the southern hemisphere (Ohneiser et al, 2022a). In this particular situation, localized causes had global and longer-term effects, which is why the Australian fires are compared to strong volcanic eruptions in the literature (Hirsch and Koren, 2021;Liu et al, 2022).…”

Section: Discussionmentioning

confidence: 99%

“…Its instantaneous positive radiative forcing in the southern hemisphere was estimated as high as +0.5 W m −2 by Heinold et al (2022). The actual radiative effect by the smoke aerosol would however be moderated by longwave adjustments in the stratosphere (Yu et al, 2021;Liu et al, 2022).…”

Section: Introductionmentioning

confidence: 99%

“…It has been argued by Sellitto et al (2022) that the large spread can be attributed to uncertainties in the optical properties of the smoke, i.e., absorptivity and backscattered fraction. In our study, we aim to show in a complementary manner that the different assumptions used to estimate the radiative forcing, i.e., the consideration of cloud effects (Heinold et al, 2022), the contribution of adjustments to the forcing (Yu et al, 2021;Liu et al, 2022), and the spatial extent over which the averaged values were collected (applies e.g. to Hirsch and Koren, 2021;Liu et al, 2022), have significant influence on the estimated magnitude of the forcing value or even the sign of the radiative forcing.…”

Section: Introductionmentioning

confidence: 99%

“…In our study, we aim to show in a complementary manner that the different assumptions used to estimate the radiative forcing, i.e., the consideration of cloud effects (Heinold et al, 2022), the contribution of adjustments to the forcing (Yu et al, 2021;Liu et al, 2022), and the spatial extent over which the averaged values were collected (applies e.g. to Hirsch and Koren, 2021;Liu et al, 2022), have significant influence on the estimated magnitude of the forcing value or even the sign of the radiative forcing. The dynamical mechanisms that led to the formation of a synoptic-scale anticyclonic smoke-induced vortex appear to be well understood (Khaykin et al, 2020;Kablick et al, 2020;Allen et al, 2020;Doglioni et al, 2022), but it is unclear how the global dispersion of smoke impacted on the global circulation of the stratosphere and whether the perturbations in the lower stratosphere could have affected the upper troposphere.…”

Section: Introductionmentioning

confidence: 99%

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

Senf

Heinold²,

Kubin³

et al. 2023

Preprint

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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.

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Section: Indications Of Global Adjustments To Smoke-radiation Interac...mentioning

confidence: 58%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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

Senf

Heinold²,

Kubin³

et al. 2023

Preprint

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Light absorption enhancement of black carbon in a pyrocumulonimbus cloud

Beeler,

Kumar,

Schwarz

et al. 2024

Nat Commun

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Pyrocumulonimbus (pyroCb) firestorm systems have been shown to inject significant amounts of black carbon (BC) to the stratosphere with a residence time of several months. Injected BC warms the local stratospheric air, consequently perturbing transport and hence spatial distributions of ozone and water vapor. A distinguishing feature of BC-containing particles residing within pyroCb smoke is their thick surface coatings made of condensed organic matter. When coated with non-refractory materials, BC’s absorption is enhanced, yet the absorption enhancement factor (Eabs) for pyroCb BC is not well constrained. Here, we perform particle-scale measurements of BC mass, morphology, and coating thickness from inside a pyroCb cloud and quantify Eabs using an established particle-resolved BC optics model. We find that the population-averaged Eabs for BC asymptotes to 2.0 with increasing coating thickness. This value denotes the upper limit of Eabs for thickly coated BC in the atmosphere. Our results provide observationally constrained parameterizations of BC absorption for improved radiative transfer calculations of pyroCb events.

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Divergent features of the upper-tropospheric carbonaceous aerosol layer: effects of atmospheric dynamics and pollution emissions in Asia, South America, and Africa

Wu,

Yan,

Zhang

et al. 2024

Environ. Res. Lett.

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The upper-tropospheric carbonaceous aerosol layer (TCAL) represents the increase of aerosols in the upper-troposphere. It was first discovered over Asia but was found in this study to also occur over South America and Africa. The TCALs over three regions typically exist during the strong deep convection season, with the Asian, South American, and African TCALs showing peak intensity during July–August, October–December, and November–December, respectively. Over Asia, the TCAL has the highest altitude and widest spread due to strongest deep convection and upper-troposphere anticyclonic system. TCAL intensity is highest in South America maybe due to heaviest pollutant emissions. Anthropogenic pollution from India and western China produces two Asian TCAL centers, whereas widespread wildfires result in single centers over South America and Africa. TCAL radiative effect at the top of the atmosphere has warming effects over Asia (+0.23 W m−2), whereas cooling effects perform over South America (−0.54 W m−2) and Africa (−0.20 W m−2) owing to its altitude and the divergent strengths of black-carbon absorption and organic-carbon scattering.

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Significant Effective Radiative Forcing of Stratospheric Wildfire Smoke

Abstract: The pyrocumulonimbus (pyroCb) induced by extreme wildfires can inject many smoke particles into the stratosphere (

Cited by 7 publications

References 61 publications

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

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

Light absorption enhancement of black carbon in a pyrocumulonimbus cloud

Divergent features of the upper-tropospheric carbonaceous aerosol layer: effects of atmospheric dynamics and pollution emissions in Asia, South America, and Africa

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