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| Titel |
The scientific basis for a satellite mission to retrieve CCN concentrations and their impacts on convective clouds |
| VerfasserIn |
D. Rosenfeld, E. Williams, M. O. Andreae, E. Freud, U. Pöschl, N. O. Rennó |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 5, no. 8 ; Nr. 5, no. 8 (2012-08-23), S.2039-2055 |
| Datensatznummer |
250003055
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| Publikation (Nr.) |
 copernicus.org/amt-5-2039-2012.pdf |
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| Zusammenfassung |
| The cloud-mediated aerosol radiative forcing is widely recognized as the
main source of uncertainty in our knowledge of the anthropogenic forcing on
climate. The current challenges for improving our understanding are (1)
global measurements of cloud condensation nuclei (CCN) in the cloudy
boundary layer from space, and (2) disentangling the effects of aerosols
from the thermodynamic and meteorological effects on the clouds. Here, we
present a new conceptual framework to help us overcome these two challenges,
using relatively simple passive satellite measurements in the visible and
infared (IR). The idea is to use the clouds themselves as natural CCN chambers by
retrieving simultaneously the number of activated aerosols at cloud base,
Na, and the cloud base updraft speed. The Na is obtained by
analyzing the distribution of cloud drop effective radius in convective
elements as a function of distance above cloud base. The cloud base updraft
velocities are estimated by double stereoscopic viewing and tracking of the
evolution of cloud surface features just above cloud base. In order to
resolve the vertical dimension of the clouds, the field of view will be 100
m for the microphysical retrievals, and 50 m for the stereoscopic
measurements. The viewing geometry will be eastward and 30 degrees off
nadir, with the Sun in the back at 30 degrees off zenith westward, requiring
a Sun-synchronous orbit at 14 LST. Measuring simultaneously the
thermodynamic environment, the vertical motions of the clouds, their
microstructure and the CCN concentration will allow separating the dynamics
from the CCN effects. This concept is being applied in the proposed
satellite mission named Clouds, Hazards and Aerosols Survey for Earth
Researchers (CHASER). |
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