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| Titel |
The effects of timing and rate of marine cloud brightening aerosol injection on albedo changes during the diurnal cycle of marine stratocumulus clouds |
| VerfasserIn |
A. K. L. Jenkins, P. M. Forster, L. S. Jackson |
| 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 ; 13, no. 3 ; Nr. 13, no. 3 (2013-02-08), S.1659-1673 |
| Datensatznummer |
250017653
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| Publikation (Nr.) |
 copernicus.org/acp-13-1659-2013.pdf |
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| Zusammenfassung |
| The marine-cloud brightening geoengineering technique has been suggested as
a possible means of counteracting the positive radiative forcing associated
with anthropogenic atmospheric CO2 increases. The focus of this study
is to quantify the albedo response to aerosols injected into marine
stratocumulus cloud from a point source at different times of day. We use a
cloud-resolving model to investigate both weakly precipitating and
non-precipitating regimes. Injection into both regimes induces a first
indirect aerosol effect. Additionally, the weakly precipitating regime shows
evidence of liquid water path gain associated with a second indirect aerosol
effect that contributes to a more negative radiative forcing, and cloud
changes indicative of a regime change to more persistent cloud. This results
in a cloud albedo increase up to six times larger than in the
non-precipitating case. These indirect effects show considerable variation
with injection at different times in the diurnal cycle. For the weakly
precipitating case, aerosol injection results in domain average increases in
cloud albedo of 0.28 and 0.17 in the early and mid morning (03:00:00 local
time (LT) and 08:00:00 LT respectively) and 0.01 in the evening (18:00:00
LT). No cloud develops when injecting into the cloud-free early afternoon
(13:00:00 LT). However, the all-sky albedo increases (which include both the
indirect and direct aerosol effects) are highest for early morning injection
(0.11). Mid-morning and daytime injections produce increases of 0.06, with
the direct aerosol effect compensating for the lack of cloud albedo
perturbation during the cloud-free early afternoon. Evening injection
results in an increase of 0.04. For the weakly precipitating case
considered, the optimal injection time for planetary albedo response is the
early morning. Here, the cloud has more opportunity develop into a more
persistent non-precipitating regime prior to the dissipative effects of
solar heating. The effectiveness of the sea-spray injection method is highly
sensitive to diurnal injection time and the direct aerosol effect of an
intense aerosol point source. Studies which ignore these factors could
overstate the effectiveness of the marine cloud brightening technique. |
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