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| Titel |
Simultaneous retrieval of aerosol and cloud properties during the MILAGRO field campaign |
| VerfasserIn |
K. Knobelspiesse, B. Cairns, J. Redemann, R. W. Bergstrom, A. Stohl |
| 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 ; 11, no. 13 ; Nr. 11, no. 13 (2011-07-01), S.6245-6263 |
| Datensatznummer |
250009883
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| Publikation (Nr.) |
 copernicus.org/acp-11-6245-2011.pdf |
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| Zusammenfassung |
| Estimation of Direct Climate Forcing (DCF) due to aerosols in cloudy areas
has historically been a difficult task, mainly because of a lack of
appropriate measurements. Recently, passive remote sensing instruments have
been developed that have the potential to retrieve both cloud and aerosol
properties using polarimetric, multiple view angle, and multi spectral
observations, and therefore determine DCF from aerosols above clouds. One
such instrument is the Research Scanning Polarimeter (RSP), an airborne
prototype of a sensor on the NASA Glory satellite, which unfortunately failed
to reach orbit during its launch in March of 2011. In the spring of 2006, the
RSP was deployed on an aircraft based in Veracruz, Mexico, as part of the
Megacity Initiative: Local and Global Research Observations (MILAGRO) field
campaign. On 13 March, the RSP over flew an aerosol layer lofted above a
low altitude marine stratocumulus cloud close to shore in the Gulf of Mexico.
We investigate the feasibility of retrieving aerosol properties over clouds
using these data. Our approach is to first determine cloud droplet size
distribution using the angular location of the cloud bow and other features
in the polarized reflectance. The selected cloud was then used in a multiple
scattering radiative transfer model optimization to determine the aerosol
optical properties and fine tune the cloud size distribution. In this scene,
we were able to retrieve aerosol optical depth, the fine mode aerosol size
distribution parameters and the cloud droplet size distribution parameters to
a degree of accuracy required for climate modeling. This required assumptions
about the aerosol vertical distribution and the optical properties of the
coarse aerosol size mode. A sensitivity study was also performed to place
this study in the context of future systematic scanning polarimeter
observations, which found that the aerosol complex refractive index can also
be observed accurately if the aerosol optical depth is larger than roughly
0.8 at a wavelength of (0.555 μm). |
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