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| Titel |
A global survey of cloud overlap based on CALIPSO and CloudSat measurements |
| VerfasserIn |
J. Li, J. Huang, K. Stamnes, T. Wang, Q. Lv, H. Jin |
| 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 ; 15, no. 1 ; Nr. 15, no. 1 (2015-01-15), S.519-536 |
| Datensatznummer |
250119310
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| Publikation (Nr.) |
 copernicus.org/acp-15-519-2015.pdf |
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| Zusammenfassung |
Using 2B-CLDCLASS-LIDAR (radar–lidar) cloud classification and
2B-FLXHR-LIDAR radiation products from CloudSat over 4 years, this study
evaluates the co-occurrence frequencies of different cloud types, analyzes
their along-track horizontal scales and cloud radiative effects (CREs), and
utilizes the vertical distributions of cloud types to evaluate cloud-overlap
assumptions.
The statistical results show that high clouds, altostratus (As), altocumulus
(Ac) and cumulus (Cu) tend to coexist with other cloud types. However,
stratus (St) (or stratocumulus, Sc), nimbostratus (Ns) and convective clouds
are much more likely to exhibit individual features than other cloud types.
On average, altostratus-over-stratus/stratocumulus cloud systems have a
maximum horizontal scale of 17.4 km, with a standard deviation of 23.5 km.
Altocumulus-over-cumulus cloud types have a minimum scale of 2.8 km,
with a standard deviation of 3.1 km. By considering the weight of each
multilayered cloud type, we find that the global mean instantaneous net CREs
of multilayered cloud systems during the daytime are approximately −41.3
and −50.2 W m−2, which account for 40.1 and 42.3% of the global
mean total net CREs at the top of the atmosphere (TOA) and at the surface,
respectively. The radiative contributions of high-over-altocumulus and
high-over-stratus/stratocumulus (or cumulus) in the all multilayered cloud
systems are dominant due to their frequency.
Considering the overlap of cloud types, the cloud fraction based on the
random overlap assumption is underestimated over vast oceans, except in the
west-central Pacific Ocean warm pool. Obvious overestimations mainly occur
over tropical and subtropical land masses. In view of a lower degree of
overlap than that predicted by the random overlap assumption to occur over the
vast ocean, particularly poleward of 40° S, the study therefore
suggests that a linear combination of minimum and random overlap assumptions
may further improve the predictions of actual cloud fractions for
multilayered cloud types (e.g., As + St/Sc and
Ac + St/Sc) over the Southern Ocean. The establishment of
a statistical relationship between multilayered cloud types and the
environmental conditions (e.g., atmospheric vertical motion, convective
stability and wind shear) would be useful for parameterization design of
cloud overlap in numerical models. |
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