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| Titel |
A study of aerosol indirect effects and feedbacks on convective precipitation |
| VerfasserIn |
Nicolas Da Silva, Sylvain Mailler, Philippe Drobinski |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250145183
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| Publikation (Nr.) |
 EGU/EGU2017-9097.pdf |
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| Zusammenfassung |
| Atmospheric aerosols from natural and anthropogenic origin are present in the troposphere of
the Mediterranean basin and continental Europe, occasionnally reaching very high
concentrations in air masses with a strong content of aerosols related to mineral
dust emissions, wildfires, or anthropogenic contamination [1]. On the other hand
precipitations in the Mediterranean basin need to be understood precisely since drought
and extreme precipitation events are a part of Mediterranean climate which can
strongly affect the people and the economic activity in the Mediterranean basin
[2].
The present study is a contribution to the investigations on the effects of aerosols on
precipitation in the Mediterranean basin and continental Europe. For that purpose, we used
the Weather Research and Forecasting Model (WRF) parameterized with the Thompson
aerosol-aware microphysics schemes, performing two sensitivity simulations forced with two
different aerosol climatologies during six months covering an entire summer season on a
domain, covering the Mediterranean basin and continental Europe at 50 km resolution.
Aerosols may affect atmospheric dynamics through their direct and semidirect
radiative effects as well as through their indirect effects (through the changes of cloud
microphysics). While it is difficult to disentangle these differents effects in reality, numerical
modelling with the WRF model make it possible to isolate indirect effects by modifying
them without affecting the direct or semidirect effects of aerosols in an attempt
to examine the effect of aerosols on precipitations through microphysical effects
only.
Our first results have shown two opposite responses depending whether the precipitation
are convective or large-scale. Since convective precipitations seem to be clearly inhibited by
increased concentrations of cloud-condensation nuclei, we attempted to understand which
processes and feedbacks are involved in this reduction of parameterized convective
precipitations when the concentrations of cloud-condensation nuclei are increased. We
diagnosed a complex feedback chain beginning from the reduction of mean droplet radii,
yielding an increase of atmospheric stability and also lowering the humidity available in the
planetary boundary layer for the formation of convective clouds and precipitations. These
results suggest that the microphysical effect of aerosols may contribute to a reduction of
convective precipitation mostly through modifications in thermodynamic vertical
profiles.
References
[1] G. Rea, S. Turquety, L. Menut, R. Briant, S. Mailler, and G. Siour. Source
contributions to 2012 summertime aerosols in the euro-mediterranean region.
Atmospheric Chemistry and Physics, 15(14):8013–8036, 2015.
[2] F. Giorgi. Climate change hot-spots. Geophysical Research Letters, 33(8):
L08707, 2006. |
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