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| Titel |
Lidar multiple scattering factors inferred from CALIPSO lidar and IIR retrievals of semi-transparent cirrus cloud optical depths over oceans |
| VerfasserIn |
A. Garnier, J. Pelon, M. A. Vaughan, D. M. Winker, C. R. Trepte, P. Dubuisson |
| 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 ; 8, no. 7 ; Nr. 8, no. 7 (2015-07-15), S.2759-2774 |
| Datensatznummer |
250116478
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| Publikation (Nr.) |
 copernicus.org/amt-8-2759-2015.pdf |
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| Zusammenfassung |
| Cirrus cloud absorption optical depths retrieved at 12.05 μm are
compared to extinction optical depths retrieved at 0.532 μm from
perfectly co-located observations of single-layered semi-transparent cirrus
over ocean made by the Imaging Infrared Radiometer (IIR) and the Cloud and
Aerosol Lidar with Orthogonal Polarization (CALIOP) flying on board the
CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations)
satellite. IIR infrared absorption optical depths are compared to CALIOP
visible extinction optical depths when the latter can be directly derived
from the measured apparent two-way transmittance through the cloud. An
evaluation of the CALIOP multiple scattering factor
is inferred from these comparisons after assessing and correcting biases in
IIR and CALIOP optical depths reported in version 3 data products. In
particular, the blackbody radiance taken in the IIR version 3 algorithm is
evaluated, and IIR retrievals are corrected accordingly. Numerical
simulations and IIR retrievals of ice crystal sizes suggest that the ratios
of CALIOP extinction and IIR absorption optical depths should remain roughly
constant with respect to temperature. Instead, these ratios are found to
increase quasi-linearly by about 40 % as the temperature at the layer
centroid altitude decreases from 240 to 200 K. It is discussed that this
behavior can be explained by variations of the multiple scattering factor
ηT applied to correct the measured apparent two-way
transmittance for contribution of forward-scattering. While the CALIOP
version 3 retrievals hold ηT fixed at 0.6, this study shows
that ηT varies with temperature (and hence cloud particle
size) from ηT = 0.8 at 200 K to ηT = 0.5 at
240 K for single-layered semi-transparent cirrus clouds with optical depth
larger than 0.3. The revised parameterization of ηT introduces
a concomitant temperature dependence in the simultaneously derived CALIOP
lidar ratios that is consistent with observed changes in CALIOP
depolarization ratios and particle habits derived from IIR measurements. |
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