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| Titel |
Moisture and dynamical interactions maintaining decoupled Arctic mixed-phase stratocumulus in the presence of a humidity inversion |
| VerfasserIn |
A. Solomon, M. D. Shupe, P. O. G. Persson, H. Morrison |
| 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 ; 11, no. 19 ; Nr. 11, no. 19 (2011-10-07), S.10127-10148 |
| Datensatznummer |
250010116
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| Publikation (Nr.) |
 copernicus.org/acp-11-10127-2011.pdf |
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| Zusammenfassung |
| Observations suggest that processes maintaining subtropical and Arctic
stratocumulus differ, due to the different environments in which they occur.
For example, specific humidity inversions (specific humidity increasing with
height) are frequently observed to occur near cloud top coincident with
temperature inversions in the Arctic, while they do not occur in the
subtropics. In this study we use nested LES simulations of decoupled Arctic
Mixed-Phase Stratocumulus (AMPS) clouds observed during the DOE Atmospheric
Radiation Measurement Program's Indirect and SemiDirect Aerosol Campaign
(ISDAC) to analyze budgets of water components, potential temperature, and
turbulent kinetic energy. These analyses quantify the processes that
maintain decoupled AMPS, including the role of humidity inversions. Key
structural features include a shallow upper entrainment zone at cloud top
that is located within the temperature and humidity inversions, a mixed
layer driven by cloud-top cooling that extends from the base of the upper
entrainment zone to below cloud base, and a lower entrainment zone at the
base of the mixed layer. The surface layer below the lower entrainment zone
is decoupled from the cloud mixed-layer system. Budget results show that
cloud liquid water is maintained in the upper entrainment zone near cloud
top (within a temperature and humidity inversion) due to a down gradient
transport of water vapor by turbulent fluxes into the cloud layer from above
and direct condensation forced by radiative cooling. Liquid water is
generated in the updraft portions of the mixed-layer eddies below cloud top
by buoyant destabilization. These processes cause at least 20% of the
cloud liquid water to extend into the inversion. The redistribution of water
vapor from the top of the humidity inversion to its base maintains the cloud
layer, while the mixed layer-entrainment zone system is continually losing
total water. In this decoupled system, the humidity inversion is the only
source of water vapor for the cloud system, since water vapor from the
surface layer is not efficiently transported into the mixed layer.
Sedimentation of ice is the dominant sink of moisture from the mixed layer. |
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