Less atmospheric radiative heating by dust due to the synergy of coarser size and aspherical shape

<p>Mineral dust aerosols cool and warm the atmosphere by scattering and absorbing solar (shortwave: SW) and thermal (longwave: LW) radiation. However, significant uncertainties remain in dust radiative effects, largely due to differences in the dust size distribution and spectral optical prope...

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Autores principales:	A. Ito, A. A. Adebiyi, Y. Huang, J. F. Kok
Formato:	article
Lenguaje:	EN
Publicado:	Copernicus Publications 2021
Materias:	Physics QC1-999 Chemistry QD1-999
Acceso en línea:	https://doaj.org/article/4198065ebe0f4adaa6b528dd3c8ac88a
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spelling	oai:doaj.org-article:4198065ebe0f4adaa6b528dd3c8ac88a2021-11-19T07:51:20ZLess atmospheric radiative heating by dust due to the synergy of coarser size and aspherical shape10.5194/acp-21-16869-20211680-73161680-7324https://doaj.org/article/4198065ebe0f4adaa6b528dd3c8ac88a2021-11-01T00:00:00Zhttps://acp.copernicus.org/articles/21/16869/2021/acp-21-16869-2021.pdfhttps://doaj.org/toc/1680-7316https://doaj.org/toc/1680-7324<p>Mineral dust aerosols cool and warm the atmosphere by scattering and absorbing solar (shortwave: SW) and thermal (longwave: LW) radiation. However, significant uncertainties remain in dust radiative effects, largely due to differences in the dust size distribution and spectral optical properties simulated in Earth system models. Dust models typically underestimate the coarse dust load (more than 2.5 <span class="inline-formula">µm</span> in diameter) and assume a spherical shape, which leads to an overestimate of the fine dust load (less than 2.5 <span class="inline-formula">µm</span>) after the dust emissions in the models are scaled to match observed dust aerosol optical depth at 550 nm (DAOD<span class="inline-formula"><sub>550</sub></span>). Here, we improve the simulated dust properties with data sets that leverage measurements of size-resolved dust concentration, asphericity factor, and refractive index in a coupled global chemical transport model with a radiative transfer module. After the adjustment of size-resolved dust concentration and spectral optical properties, the global and annual average of DAOD<span class="inline-formula"><sub>550</sub></span> from the simulation increases from 0.023 to 0.029 and falls within the range of a semi-observationally based estimate (0.030 <span class="inline-formula">±</span> 0.005). The reduction of fine dust load after the adjustment leads to a reduction of the SW cooling at the top of the atmosphere (TOA). To improve agreement against a semi-observationally based estimate of the radiative effect efficiency at TOA, we find that a less absorptive SW dust refractive index is required for coarser aspherical dust. Thus, only a minor difference is estimated for the net global dust radiative effect at TOA (<span class="inline-formula">−</span>0.08 vs. <span class="inline-formula">−</span>0.00 W m<span class="inline-formula"><sup>−2</sup></span> on a global scale). Conversely, our sensitivity simulations reveal that the surface warming is substantially enhanced near the strong dust source regions (less cooling to <span class="inline-formula">−</span>0.23 from <span class="inline-formula">−</span>0.60 W m<span class="inline-formula"><sup>−2</sup></span> on a global scale). Thus, less atmospheric radiative heating is estimated near the major source regions (less heating to 0.15 from 0.59 W m<span class="inline-formula"><sup>−2</sup></span> on a global scale), because of enhanced LW warming at the surface by the synergy of coarser size and aspherical shape.</p>A. ItoA. A. AdebiyiY. HuangY. HuangY. HuangJ. F. KokCopernicus PublicationsarticlePhysicsQC1-999ChemistryQD1-999ENAtmospheric Chemistry and Physics, Vol 21, Pp 16869-16891 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Physics QC1-999 Chemistry QD1-999
spellingShingle	Physics QC1-999 Chemistry QD1-999 A. Ito A. A. Adebiyi Y. Huang Y. Huang Y. Huang J. F. Kok Less atmospheric radiative heating by dust due to the synergy of coarser size and aspherical shape
description	<p>Mineral dust aerosols cool and warm the atmosphere by scattering and absorbing solar (shortwave: SW) and thermal (longwave: LW) radiation. However, significant uncertainties remain in dust radiative effects, largely due to differences in the dust size distribution and spectral optical properties simulated in Earth system models. Dust models typically underestimate the coarse dust load (more than 2.5 <span class="inline-formula">µm</span> in diameter) and assume a spherical shape, which leads to an overestimate of the fine dust load (less than 2.5 <span class="inline-formula">µm</span>) after the dust emissions in the models are scaled to match observed dust aerosol optical depth at 550 nm (DAOD<span class="inline-formula"><sub>550</sub></span>). Here, we improve the simulated dust properties with data sets that leverage measurements of size-resolved dust concentration, asphericity factor, and refractive index in a coupled global chemical transport model with a radiative transfer module. After the adjustment of size-resolved dust concentration and spectral optical properties, the global and annual average of DAOD<span class="inline-formula"><sub>550</sub></span> from the simulation increases from 0.023 to 0.029 and falls within the range of a semi-observationally based estimate (0.030 <span class="inline-formula">±</span> 0.005). The reduction of fine dust load after the adjustment leads to a reduction of the SW cooling at the top of the atmosphere (TOA). To improve agreement against a semi-observationally based estimate of the radiative effect efficiency at TOA, we find that a less absorptive SW dust refractive index is required for coarser aspherical dust. Thus, only a minor difference is estimated for the net global dust radiative effect at TOA (<span class="inline-formula">−</span>0.08 vs. <span class="inline-formula">−</span>0.00 W m<span class="inline-formula"><sup>−2</sup></span> on a global scale). Conversely, our sensitivity simulations reveal that the surface warming is substantially enhanced near the strong dust source regions (less cooling to <span class="inline-formula">−</span>0.23 from <span class="inline-formula">−</span>0.60 W m<span class="inline-formula"><sup>−2</sup></span> on a global scale). Thus, less atmospheric radiative heating is estimated near the major source regions (less heating to 0.15 from 0.59 W m<span class="inline-formula"><sup>−2</sup></span> on a global scale), because of enhanced LW warming at the surface by the synergy of coarser size and aspherical shape.</p>
format	article
author	A. Ito A. A. Adebiyi Y. Huang Y. Huang Y. Huang J. F. Kok
author_facet	A. Ito A. A. Adebiyi Y. Huang Y. Huang Y. Huang J. F. Kok
author_sort	A. Ito
title	Less atmospheric radiative heating by dust due to the synergy of coarser size and aspherical shape
title_short	Less atmospheric radiative heating by dust due to the synergy of coarser size and aspherical shape
title_full	Less atmospheric radiative heating by dust due to the synergy of coarser size and aspherical shape
title_fullStr	Less atmospheric radiative heating by dust due to the synergy of coarser size and aspherical shape
title_full_unstemmed	Less atmospheric radiative heating by dust due to the synergy of coarser size and aspherical shape
title_sort	less atmospheric radiative heating by dust due to the synergy of coarser size and aspherical shape
publisher	Copernicus Publications
publishDate	2021
url	https://doaj.org/article/4198065ebe0f4adaa6b528dd3c8ac88a
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_version_	1718420254591287296

Less atmospheric radiative heating by dust due to the synergy of coarser size and aspherical shape

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