Exploring the uncertainties in the aviation soot–cirrus effect
<p>A global aerosol–climate model, including a two-moment cloud microphysical scheme and a parametrization for aerosol-induced ice formation in cirrus clouds, is applied in order to quantify the impact of aviation soot on natural cirrus clouds. Several sensitivity experiments are performed to...
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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/6a9eb7ba3ed14e5682a14751bdf8dc28 |
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| Sumario: | <p>A global aerosol–climate model, including a two-moment cloud microphysical
scheme and a parametrization for aerosol-induced ice formation in cirrus
clouds, is applied in order to quantify the impact of aviation soot on natural
cirrus clouds. Several sensitivity experiments are performed to assess the
uncertainties in this effect related to (i) the assumptions on the ice
nucleation abilities of aviation soot, (ii) the representation of vertical
updrafts in the model, and (iii) the use of reanalysis data to relax the model
dynamics (the so-called nudging technique). Based on the results of the model
simulations, a radiative forcing from the aviation soot–cirrus effect in the
range of <span class="inline-formula">−35</span> to <span class="inline-formula">13</span> mW m<span class="inline-formula"><sup>−2</sup></span> is quantified, depending on
the assumed critical saturation ratio for ice nucleation and active fraction of
aviation soot but with a confidence level below 95 % in several cases. Simple
idealized experiments with prescribed vertical velocities further show that the
uncertainties on this aspect of the model dynamics are critical for the
investigated effect and could potentially add a factor of about 2 of further
uncertainty to the model estimates of the resulting radiative forcing. The use
of the nudging technique to relax model dynamics is proved essential in order
to identify a statistically significant signal from the model internal
variability, while simulations performed in free-running mode and with
prescribed sea-surface temperatures and sea-ice concentrations are shown to be
unable to provide robust estimates of the investigated effect. A comparison
with analogous model studies on the aviation soot–cirrus effect show a very
large model diversity, with a conspicuous lack of consensus across the various
estimates, which points to the need for more in-depth analyses on the roots of
such discrepancies.</p> |
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