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| Titel |
Comparison of ice cloud properties simulated by the Community Atmosphere Model (CAM5) with in-situ observations |
| VerfasserIn |
T. Eidhammer, H. Morrison, A. Bansemer, A. Gettelman, A. J. Heymsfield |
| 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 ; 14, no. 18 ; Nr. 14, no. 18 (2014-09-23), S.10103-10118 |
| Datensatznummer |
250119058
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| Publikation (Nr.) |
 copernicus.org/acp-14-10103-2014.pdf |
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| Zusammenfassung |
| Detailed measurements of ice crystals in cirrus clouds were used to compare
with results from the Community Atmospheric Model Version 5 (CAM5) global
climate model. The observations are from two different field campaigns with
contrasting conditions: Atmospheric Radiation Measurements Spring Cloud
Intensive Operational Period in 2000 (ARM-IOP), which was characterized
primarily by midlatitude frontal clouds and cirrus, and Tropical Composition,
Cloud and Climate Coupling (TC4), which was dominated by anvil cirrus.
Results show that the model typically overestimates the slope parameter of
the exponential size distributions of cloud ice and snow, while the variation
with temperature (height) is comparable. The model also overestimates the
ice/snow number concentration (0th moment of the size distribution) and
underestimates higher moments (2nd through 5th), but compares well with
observations for the 1st moment. Overall the model shows better agreement
with observations for TC4 than for ARM-IOP in regards to the moments. The
mass-weighted terminal fall speed is lower in the model compared to
observations for both ARM-IOP and TC4, which is partly due to the
overestimation of the size distribution slope parameter. Sensitivity tests
with modification of the threshold size for cloud ice to snow autoconversion
(Dcs) do not show noticeable improvement in modeled moments,
slope parameter and mass weighed fall speed compared to observations. Further,
there is considerable sensitivity of the cloud radiative forcing to
Dcs, consistent with previous studies, but no value of
Dcs improves modeled cloud radiative forcing compared to
measurements. Since the autoconversion of cloud ice to snow using the
threshold size Dcs has little physical basis, future improvement
to combine cloud ice and snow into a single category, eliminating the need
for autoconversion, is suggested. |
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