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| Titel |
Prognostic description of ice using a single category in the GCM ECHAM-HAM |
| VerfasserIn |
Remo Dietlicher, David Neubauer, Ulrike Lohmann |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250148366
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| Publikation (Nr.) |
 EGU/EGU2017-12616.pdf |
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| Zusammenfassung |
| A new scheme for stratiform cloud microphysics has been implemented in a general
circulation model. It features a widely used description of cloud water with the two categories
for cloud droplets and rain. The unique aspect of the scheme is the break with the traditional
approach to describe cloud ice analogously. Here we parametrize cloud ice with a single,
prognostic category, as it has been done in recent regional models. The intrinsicly hard to
parametrize processes of aggregation and accretion are replaced by the explicit
computation of ice particle collection and fall speeds within the prognosed particle size
distribution.
This work shows that a single category is a viable approach to describe cloud ice in
climate models. Performance is evaluated in idealized single column model setups as well as
global runs. We find that a nested approach for substepping the microphysics scheme yields
good results in terms of numerical stability and computational cost. The scheme is compared
to an established description of cloud ice with two categories for in-cloud ice and snow. We
find that especially in clouds where aggregation is weak but fall-speeds are not negligible due
to strong depositional growth or riming, the new scheme produces much more reasonable
results. |
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