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| Titel |
The scientific basis for a satellite mission to retrieve CCN and its impacts on convective cloud |
| VerfasserIn |
D. Rosenfeld, E. Williams, M. O. Andreae, E. Freud, U. Pöschl, N. O. Rennó |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250064253
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| Zusammenfassung |
| The cloud -mediated radiative forcing is widely recognized as the main source of uncertainty
in our knowledge of the anthropogenic climate forcing and in our understanding of climate
sensitivity. Current outstanding challenges 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 concept for a way to overcome these two challenges, using
relatively simple passive satellite measurements in the visible and 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 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
30 degrees off nadir eastward, with the Sun in the back at 30 degrees off zenith
westward, which requires a Sun synchronous orbit at 14 LST. Having measured
simultaneously the thermodynamic environment, the vertical motions of the clouds, their
microstructure and the CCN concentration will allow separating the dynamic 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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