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| Titel |
The shortwave radiative forcing bias of liquid and ice clouds from MODIS observations |
| VerfasserIn |
L. Oreopoulos, S. Platnick, G. Hong, P. Yang, R. F. Cahalan |
| 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 ; 9, no. 16 ; Nr. 9, no. 16 (2009-08-19), S.5865-5875 |
| Datensatznummer |
250007574
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| Publikation (Nr.) |
 copernicus.org/acp-9-5865-2009.pdf |
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| Zusammenfassung |
| We present an assessment of the plane-parallel bias of the shortwave cloud
radiative forcing (SWCRF) of liquid and ice clouds at 1 deg scales using
global MODIS (Terra and Aqua) cloud optical property retrievals for four
months of the year 2005 representative of the meteorological seasons. The
(negative) bias is estimated as the difference of SWCRF calculated using the
Plane-Parallel Homogeneous (PPH) approximation and the Independent Column
Approximation (ICA). PPH calculations use MODIS-derived gridpoint means
while ICA calculations use distributions of cloud optical thickness and
effective radius. Assisted by a broadband solar radiative transfer
algorithm, we find that the absolute value of global SWCRF bias of liquid
clouds at the top of the atmosphere is about 6 W m−2 for MODIS overpass
times while the SWCRF bias for ice clouds is smaller in absolute terms by
about 0.7 W m−2, but with stronger spatial variability. If effective
radius variability is neglected and only optical thickness horizontal
variations are accounted for, the absolute SWCRF biases increase by about
0.3–0.4 W m−2 on average. Marine clouds of both phases exhibit greater
(more negative) SWCRF biases than continental clouds. Finally, morning
(Terra)–afternoon (Aqua) differences in SWCRF bias are much more pronounced
for ice clouds, up to about 15% (Aqua producing stronger negative bias)
on global scales, with virtually all contribution to the difference coming
from land areas. The substantial magnitude of the global SWCRF bias, which
for clouds of both phases is collectively about 4 W m−2 for diurnal
averages, should be considered a strong motivation for global climate
modelers to accelerate efforts linking cloud schemes capable of subgrid
condensate variability with appropriate radiative transfer schemes. |
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