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| Titel |
Impact of natural and anthropogenic aerosols on stratocumulus and precipitation in the Southeast Pacific: a regional modelling study using WRF-Chem |
| VerfasserIn |
Q. Yang, W. I. Gustafson, J. D. Fast, H. Wang, R. C. Easter, M. Wang, S. J. Ghan, L. K. Berg, L. R. Leung, H. Morrison |
| 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 ; 12, no. 18 ; Nr. 12, no. 18 (2012-09-28), S.8777-8796 |
| Datensatznummer |
250011478
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| Publikation (Nr.) |
 copernicus.org/acp-12-8777-2012.pdf |
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| Zusammenfassung |
| Cloud-system resolving simulations with the chemistry version of the Weather
Research and Forecasting (WRF-Chem) model are used to quantify the relative
impacts of regional anthropogenic and oceanic emissions on changes in
aerosol properties, cloud macro- and microphysics, and cloud radiative
forcing over the Southeast Pacific (SEP) during the VAMOS
Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) (15
October–16 November 2008). Two distinct regions are identified. The near-coast
polluted region is characterized by low surface precipitation rates, the
strong suppression of non-sea-salt particle activation due to sea-salt
particles, a predominant albedo effect in aerosol indirect effects, and
limited impact of aerosols associated with anthropogenic emissions on
clouds. Opposite sensitivities to natural marine and anthropogenic aerosol
perturbations are seen in cloud properties (e.g., cloud optical depth and
cloud-top and cloud-base heights), precipitation, and the top-of-atmosphere
and surface shortwave fluxes over this region. The relatively clean remote
region is characterized by large contributions of aerosols from non-regional
sources (lateral boundaries) and much stronger drizzle at the surface. Under
a scenario of five-fold increase in regional anthropogenic emissions, this
relatively clean region shows large cloud responses, for example, a 13%
increase in cloud-top height and a 9% increase in albedo in response to a
moderate increase (25% of the reference case) in cloud condensation
nuclei (CCN) concentration. The reduction of precipitation due to this
increase in anthropogenic aerosols more than doubles the aerosol lifetime in
the clean marine boundary layer. Therefore, the aerosol impacts on
precipitation are amplified by the positive feedback of precipitation on
aerosol, which ultimately alters the cloud micro- and macro-physical
properties, leading to strong aerosol-cloud-precipitation interactions. The
high sensitivity is also related to an increase in cloud-top entrainment
rate (by 16% at night) due to the increased anthropogenic aerosols. The
simulated aerosol-cloud-precipitation interactions due to the increased
anthropogenic aerosols have a stronger diurnal cycle over the clean region
compared to the near-coast region with stronger interactions at night.
During the day, solar heating results in more frequent decoupling of the
cloud and sub-cloud layers, thinner clouds, reduced precipitation, and
reduced sensitivity to the increase in anthropogenic emissions. This study
shows the importance of natural aerosols in accurately quantifying
anthropogenic forcing within a regional modeling framework. The results of
this study also imply that the energy balance perturbations from increased
anthropogenic emissions are larger in the more susceptible clean
environment than in already polluted environment and are larger than
possible from the first indirect effect alone. |
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