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| Titel |
TTL cirrus ice water content--extinction relationships from ATTREX measurements |
| VerfasserIn |
Troy Thornberry, Andrew Rollins, Sarah Woods, Thaopaul Bui, Ru-Shan Gao |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250135063
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| Publikation (Nr.) |
 EGU/EGU2016-15862.pdf |
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| Zusammenfassung |
| Cirrus clouds cover a large fraction of the globe and play a significant role in the radiative
balance of the Earth system, but remain a source of uncertainty since their net radiative effect
varies depending on their microphysical properties. Cirrus are particularly prevalent in the
tropical central and western Pacific, where they form at the extremely cold temperatures in
the tropical tropopause layer (TTL) and result in dehydration of air as it rises into the
stratosphere. TTL cirrus typically exhibit low ice number concentrations and small particles
relative to mid-latitude cirrus, resulting in significantly lower ice water contents
(IWC).
Lidar observations of TTL cirrus produce measurements of volume extinction (σ) and
rely on empirically derived relationships to calculate cloud IWC. To date, TTL cirrus
σ–IWC relationships have been extrapolated from measurements of mid-latitude,
higher temperature clouds, or based on a limited number of observations within TTL
cirrus. In this analysis we use measurements of cirrus extinction and IWC acquired
during the Airborne Tropical Tropopause Experiment (ATTREX) mission in the
TTL over the western Pacific to derive new relationships between these parameters
for TTL cirrus that can be used to improve the determination of TTL IWC from
satellite, airborne and ground-based lidar. ATTREX yielded more than 24 hours of
sampling in TTL cirrus at temperatures below 203 K (-70˚ C). Cirrus clouds were
encountered at altitudes between 14.5 km and 17.5 km with IWC down to the ∼2
μg m−3 detection limit of the NOAA Water instrument and water vapor mixing
ratios as low as 1.5 ppm. Most TTL cirrus sampled had ice number concentrations
(INC) less than 100 L−1, and very few had INC of more than 1000 L−1. σ values
measured by the in situ cloud probes ranged from < 10−6 m−1 to ∼10−3 m−1. |
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