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| Titel |
Tropical thin cirrus and relative humidity observed by the Atmospheric Infrared Sounder |
| VerfasserIn |
B. H. Kahn, C. K. Liang, A. Eldering, A. Gettelman, Q. Yue, K. N. Liou |
| 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 ; 8, no. 6 ; Nr. 8, no. 6 (2008-03-13), S.1501-1518 |
| Datensatznummer |
250005920
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| Publikation (Nr.) |
 copernicus.org/acp-8-1501-2008.pdf |
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| Zusammenfassung |
| Global observations of cloud and humidity distributions in the upper
troposphere within all geophysical conditions are critically important in
order to monitor the present climate and to provide necessary data for
validation of climate models to project future climate change. Towards this
end, tropical oceanic distributions of thin cirrus optical depth (τ),
effective diameter (De), and relative humidity with respect to ice
(RHi) within cirrus (RHic) are simultaneously derived from the
Atmospheric Infrared Sounder (AIRS). Corresponding increases in De and
cloud temperature are shown for cirrus with τ>0.25 that
demonstrate quantitative consistency to other surface-based, in situ and
satellite retrievals. However, inferred cirrus properties are
shown to be less certain for increasingly tenuous cirrus. In-cloud
supersaturation is observed for 8–12% of thin cirrus and is several
factors higher than all-sky conditions; even higher frequencies are shown
for the coldest and thinnest cirrus. Spatial and temporal variations in
RHic correspond to cloud frequency while regional variability in
RHic is observed to be most prominent over the N. Indian Ocean basin.
The largest cloud/clear sky RHi anomalies tend to occur in dry regions
associated with vertical descent in the sub-tropics, while the smallest
occur in moist ascending regions in the tropics. The characteristics of
RHic frequency distributions depend on τ and a peak frequency is
located between 60–80% that illustrates RHic is on average biased
dry. The geometrical thickness of cirrus is typically less than the vertical
resolution of AIRS temperature and specific humidity profiles and thus leads
to the observed dry bias, shown with coincident cloud vertical structure
obtained from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite
Observation (CALIPSO). The joint distributions of thin cirrus microphysics
and humidity derived from AIRS provide unique and important regional and
global-scale insights on upper tropospheric processes not available from
surface, in situ, and other contemporary satellite observing platforms. |
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