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| Titel |
Intercomparison of aerosol-cloud-precipitation interactions in stratiform orographic mixed-phase clouds |
| VerfasserIn |
A. Muhlbauer, T. Hashino, L. Xue, A. Teller, U. Lohmann, R. M. Rasmussen, I. Geresdi, Z. Pan |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 10, no. 17 ; Nr. 10, no. 17 (2010-09-02), S.8173-8196 |
| Datensatznummer |
250008743
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| Publikation (Nr.) |
 copernicus.org/acp-10-8173-2010.pdf |
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| Zusammenfassung |
Anthropogenic aerosols serve as a source of both cloud condensation nuclei
(CCN) and ice nuclei (IN) and affect microphysical properties of clouds.
Increasing aerosol number concentrations is hypothesized to retard the cloud
droplet coalescence and the riming in mixed-phase clouds, thereby decreasing
orographic precipitation.
This study presents results from a model intercomparison of 2-D simulations of
aerosol-cloud-precipitation interactions in stratiform orographic mixed-phase
clouds. The sensitivity of orographic precipitation to changes in the aerosol
number concentrations is analysed and compared for various dynamical and
thermodynamical situations. Furthermore, the sensitivities of microphysical
processes such as coalescence, aggregation, riming and diffusional growth to
changes in the aerosol number concentrations are evaluated and compared.
The participating numerical models are the model from the Consortium for
Small-Scale Modeling (COSMO) with bulk microphysics, the Weather Research and
Forecasting (WRF) model with bin microphysics and the University of Wisconsin
modeling system (UWNMS) with a spectral ice habit prediction microphysics
scheme. All models are operated on a cloud-resolving scale with 2 km
horizontal grid spacing.
The results of the model intercomparison suggest that the sensitivity of
orographic precipitation to aerosol modifications varies greatly from case to
case and from model to model. Neither a precipitation decrease nor a
precipitation increase is found robustly in all simulations. Qualitative
robust results can only be found for a subset of the simulations but even
then quantitative agreement is scarce. Estimates of the aerosol effect on
orographic precipitation are found to range from −19% to 0% depending on
the simulated case and the model.
Similarly, riming is shown to decrease in some cases and models whereas it
increases in others, which implies that a decrease in riming with increasing
aerosol load is not a robust result. Furthermore, it is found that neither a
decrease in cloud droplet coalescence nor a decrease in riming necessarily
implies a decrease in precipitation due to compensation effects by other
microphysical pathways.
The simulations suggest that mixed-phase conditions play an important role in
buffering the effect of aerosol perturbations on cloud microphysics and
reducing the overall susceptibility of clouds and precipitation to changes in
the aerosol number concentrations. As a consequence the aerosol effect on
precipitation is suggested to be less pronounced or even inverted in regions
with high terrain (e.g., the Alps or Rocky Mountains) or in regions where
mixed-phase microphysics is important for the climatology of orographic
precipitation. |
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