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| Titel |
Simulating mixed-phase Arctic stratus clouds: sensitivity to ice initiation mechanisms |
| VerfasserIn |
I. Sednev, S. Menon, G. McFarquhar |
| 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 ; 9, no. 14 ; Nr. 9, no. 14 (2009-07-20), S.4747-4773 |
| Datensatznummer |
250007513
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| Publikation (Nr.) |
 copernicus.org/acp-9-4747-2009.pdf |
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| Zusammenfassung |
| The importance of Arctic mixed-phase clouds on radiation and the Arctic
climate is well known. However, the development of mixed-phase cloud
parameterization for use in large scale models is limited by lack of both
related observations and numerical studies using multidimensional models with
advanced microphysics that provide the basis for understanding the relative
importance of different microphysical processes that take place in
mixed-phase clouds. To improve the representation of mixed-phase cloud
processes in the GISS GCM we use the GISS single-column model coupled to a
bin resolved microphysics (BRM) scheme that was specially designed to
simulate mixed-phase clouds and aerosol-cloud interactions. Using this model
with the microphysical measurements obtained from the DOE ARM Mixed-Phase
Arctic Cloud Experiment (MPACE) campaign in October 2004 at the North Slope
of Alaska, we investigate the effect of ice initiation processes and
Bergeron-Findeisen process (BFP) on glaciation time and longevity of
single-layer stratiform mixed-phase clouds. We focus on observations taken
during 9–10 October, which indicated the presence of a single-layer
mixed-phase clouds. We performed several sets of 12-h simulations to
examine model sensitivity to different ice initiation mechanisms and evaluate
model output (hydrometeors' concentrations, contents, effective radii,
precipitation fluxes, and radar reflectivity) against measurements from the
MPACE Intensive Observing Period. Overall, the model qualitatively simulates
ice crystal concentration and hydrometeors content, but it fails to predict
quantitatively the effective radii of ice particles and their vertical
profiles. In particular, the ice effective radii are overestimated by at
least 50%. However, using the same definition as used for observations,
the effective radii simulated and that observed were more comparable. We find
that for the single-layer stratiform mixed-phase clouds simulated, process of
ice phase initiation due to freezing of supercooled water in both saturated
and subsaturated (w.r.t. water) environments is as important as primary ice
crystal origination from water vapor. We also find that the BFP is a process
mainly responsible for the rates of glaciation of simulated clouds. These
glaciation rates cannot be adequately represented by a water-ice saturation
adjustment scheme that only depends on temperature and liquid and solid
hydrometeors' contents as is widely used in bulk microphysics schemes and are
better represented by processes that also account for supersaturation changes
as the hydrometeors grow. |
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