Direct and semi-direct radiative forcing of smoke aerosols over clouds
Observations from Earth observing satellites indicate that dark carbonaceous aerosols that absorb solar radiation are widespread in the tropics and subtropics. When these aerosols mix with clouds, there is generally a reduction of cloudiness owing to absorption of solar energy in the aerosol layer....
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ftdoajarticles:oai:doaj.org/article:ba64a38bff704f78822d2a8a97ebc1b3 2023-05-15T18:21:17+02:00 Direct and semi-direct radiative forcing of smoke aerosols over clouds E. M. Wilcox 2012-01-01T00:00:00Z https://doi.org/10.5194/acp-12-139-2012 https://doaj.org/article/ba64a38bff704f78822d2a8a97ebc1b3 EN eng Copernicus Publications http://www.atmos-chem-phys.net/12/139/2012/acp-12-139-2012.pdf https://doaj.org/toc/1680-7316 https://doaj.org/toc/1680-7324 doi:10.5194/acp-12-139-2012 1680-7316 1680-7324 https://doaj.org/article/ba64a38bff704f78822d2a8a97ebc1b3 Atmospheric Chemistry and Physics, Vol 12, Iss 1, Pp 139-149 (2012) Physics QC1-999 Chemistry QD1-999 article 2012 ftdoajarticles https://doi.org/10.5194/acp-12-139-2012 2022-12-30T22:14:33Z Observations from Earth observing satellites indicate that dark carbonaceous aerosols that absorb solar radiation are widespread in the tropics and subtropics. When these aerosols mix with clouds, there is generally a reduction of cloudiness owing to absorption of solar energy in the aerosol layer. Over the subtropical South Atlantic Ocean, where smoke from savannah burning in southern Africa resides above a persistent deck of marine stratocumulus clouds, radiative heating of the smoke layer leads to a thickening of the cloud layer. Here, satellite observations of the albedo of overcast scenes of 25 km 2 size or larger are combined with additional satellite observations of clouds and aerosols to estimate the top-of-atmosphere direct radiative forcing attributable to presence of dark aerosol above bright cloud, and the negative semi-direct forcing attributable to the thickening of the cloud layer. The average positive direct radiative forcing by smoke over an overcast scene is 9.2±6.6 W m −2 for cases with an unambiguous signal of absorbing aerosol over cloud in passive ultraviolet remote sensing observations. However, cloud liquid water path is enhanced by 16.3±7.7 g m −2 across the range of values for sea surface temperature for cases of smoke over cloud. The negative radiative forcing associated with this semi-direct effect of smoke over clouds is estimated to be −5.9±3.5 W m −2 . Therefore, the cooling associated with the semi-direct cloud thickening effect compensates for greater than 60 % of the direct radiative effect. Accounting for the frequency of occurrence of significant absorbing aerosol above overcast scenes leads to an estimate of the average direct forcing of 1.0±0.7 W m −2 contributed by these scenes averaged over the subtropical southeast Atlantic Ocean during austral winter. The regional average of the negative semi-direct forcing is −0.7±0.4 W m −2 . Therefore, smoke aerosols overlaying the decks of overcast marine stratocumulus clouds considered here yield a small net positive radiative ... Article in Journal/Newspaper South Atlantic Ocean Directory of Open Access Journals: DOAJ Articles Austral Atmospheric Chemistry and Physics 12 1 139 149 |
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Physics QC1-999 Chemistry QD1-999 |
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Physics QC1-999 Chemistry QD1-999 E. M. Wilcox Direct and semi-direct radiative forcing of smoke aerosols over clouds |
topic_facet |
Physics QC1-999 Chemistry QD1-999 |
description |
Observations from Earth observing satellites indicate that dark carbonaceous aerosols that absorb solar radiation are widespread in the tropics and subtropics. When these aerosols mix with clouds, there is generally a reduction of cloudiness owing to absorption of solar energy in the aerosol layer. Over the subtropical South Atlantic Ocean, where smoke from savannah burning in southern Africa resides above a persistent deck of marine stratocumulus clouds, radiative heating of the smoke layer leads to a thickening of the cloud layer. Here, satellite observations of the albedo of overcast scenes of 25 km 2 size or larger are combined with additional satellite observations of clouds and aerosols to estimate the top-of-atmosphere direct radiative forcing attributable to presence of dark aerosol above bright cloud, and the negative semi-direct forcing attributable to the thickening of the cloud layer. The average positive direct radiative forcing by smoke over an overcast scene is 9.2±6.6 W m −2 for cases with an unambiguous signal of absorbing aerosol over cloud in passive ultraviolet remote sensing observations. However, cloud liquid water path is enhanced by 16.3±7.7 g m −2 across the range of values for sea surface temperature for cases of smoke over cloud. The negative radiative forcing associated with this semi-direct effect of smoke over clouds is estimated to be −5.9±3.5 W m −2 . Therefore, the cooling associated with the semi-direct cloud thickening effect compensates for greater than 60 % of the direct radiative effect. Accounting for the frequency of occurrence of significant absorbing aerosol above overcast scenes leads to an estimate of the average direct forcing of 1.0±0.7 W m −2 contributed by these scenes averaged over the subtropical southeast Atlantic Ocean during austral winter. The regional average of the negative semi-direct forcing is −0.7±0.4 W m −2 . Therefore, smoke aerosols overlaying the decks of overcast marine stratocumulus clouds considered here yield a small net positive radiative ... |
format |
Article in Journal/Newspaper |
author |
E. M. Wilcox |
author_facet |
E. M. Wilcox |
author_sort |
E. M. Wilcox |
title |
Direct and semi-direct radiative forcing of smoke aerosols over clouds |
title_short |
Direct and semi-direct radiative forcing of smoke aerosols over clouds |
title_full |
Direct and semi-direct radiative forcing of smoke aerosols over clouds |
title_fullStr |
Direct and semi-direct radiative forcing of smoke aerosols over clouds |
title_full_unstemmed |
Direct and semi-direct radiative forcing of smoke aerosols over clouds |
title_sort |
direct and semi-direct radiative forcing of smoke aerosols over clouds |
publisher |
Copernicus Publications |
publishDate |
2012 |
url |
https://doi.org/10.5194/acp-12-139-2012 https://doaj.org/article/ba64a38bff704f78822d2a8a97ebc1b3 |
geographic |
Austral |
geographic_facet |
Austral |
genre |
South Atlantic Ocean |
genre_facet |
South Atlantic Ocean |
op_source |
Atmospheric Chemistry and Physics, Vol 12, Iss 1, Pp 139-149 (2012) |
op_relation |
http://www.atmos-chem-phys.net/12/139/2012/acp-12-139-2012.pdf https://doaj.org/toc/1680-7316 https://doaj.org/toc/1680-7324 doi:10.5194/acp-12-139-2012 1680-7316 1680-7324 https://doaj.org/article/ba64a38bff704f78822d2a8a97ebc1b3 |
op_doi |
https://doi.org/10.5194/acp-12-139-2012 |
container_title |
Atmospheric Chemistry and Physics |
container_volume |
12 |
container_issue |
1 |
container_start_page |
139 |
op_container_end_page |
149 |
_version_ |
1766200463453061120 |