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| Titel |
Sensitivity of remote aerosol distributions to representation of cloud–aerosol interactions in a global climate model |
| VerfasserIn |
H. Wang, R. C. Easter, P. J. Rasch, M. Wang, X. Liu, S. J. Ghan, Y. Qian, J.-H. Yoon, P.-L. Ma, V. Vinoj |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 6, no. 3 ; Nr. 6, no. 3 (2013-06-05), S.765-782 |
| Datensatznummer |
250017821
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| Publikation (Nr.) |
 copernicus.org/gmd-6-765-2013.pdf |
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| Zusammenfassung |
Many global aerosol and climate models, including the widely used Community
Atmosphere Model version 5 (CAM5), have large biases in predicting aerosols
in remote regions such as the upper troposphere and high latitudes. In this
study, we conduct CAM5 sensitivity simulations to understand the role of key
processes associated with aerosol transformation and wet removal affecting
the vertical and horizontal long-range transport of aerosols to the remote
regions. Improvements are made to processes that are currently not well
represented in CAM5, which are guided by surface and aircraft measurements
together with results from a multi-scale aerosol–climate model
that explicitly represents convection and aerosol–cloud interactions at
cloud-resolving scales. We pay particular attention to black carbon (BC) due
to its importance in the Earth system and the availability of measurements.
We introduce into CAM5 a new unified scheme for convective transport and
aerosol wet removal with explicit aerosol activation above convective cloud
base. This new implementation reduces the excessive BC aloft to better
simulate observed BC profiles that show decreasing mixing ratios in the mid-
to upper-troposphere. After implementing this new unified convective scheme,
we examine wet removal of submicron aerosols that occurs primarily through
cloud processes. The wet removal depends strongly on the subgrid-scale
liquid cloud fraction and the rate of conversion of liquid water to
precipitation. These processes lead to very strong wet removal of BC and
other aerosols over mid- to high latitudes during winter months. With our
improvements, the Arctic BC burden has a 10-fold (5-fold) increase in the
winter (summer) months, resulting in a much-better simulation of the BC
seasonal cycle as well. Arctic sulphate and other aerosol species also
increase but to a lesser extent. An explicit treatment of BC aging with
slower aging assumptions produces an additional 30-fold (5-fold) increase in
the Arctic winter (summer) BC burden. This BC aging treatment, however, has
minimal effect on other underpredicted species. Interestingly, our
modifications to CAM5 that aim at improving prediction of high-latitude and
upper-tropospheric aerosols also produce much-better aerosol optical depth
(AOD) over various other regions globally when compared to multi-year AERONET
retrievals. The improved aerosol distributions have impacts on other aspects
of CAM5, improving the simulation of global mean liquid water path and cloud
forcing. |
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