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: | , , , |
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| Formato: | article |
| Lenguaje: | EN |
| Publicado: |
Copernicus Publications
2021
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| Materias: | |
| Acceso en línea: | https://doaj.org/article/4198065ebe0f4adaa6b528dd3c8ac88a |
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| Sumario: | <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> |
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