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| Titel |
Modelling the effects of gravity waves on stratocumulus clouds observed during VOCALS-UK |
| VerfasserIn |
P. J. Connolly, G. Vaughan, P. Cook, G. Allen, H. Coe, T. W. Choularton, C. Dearden, A. Hill |
| 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 ; 13, no. 14 ; Nr. 13, no. 14 (2013-07-29), S.7133-7152 |
| Datensatznummer |
250018784
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| Publikation (Nr.) |
 copernicus.org/acp-13-7133-2013.pdf |
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| Zusammenfassung |
| During the VOCALS campaign spaceborne satellite observations showed that
travelling gravity wave packets, generated by geostrophic adjustment,
resulted in perturbations to marine boundary layer (MBL) clouds over the south-east
Pacific Ocean (SEP). Often, these perturbations were reversible in that passage of
the wave resulted in the clouds becoming brighter (in the wave crest), then
darker (in the wave trough) and subsequently recovering their properties
after the passage of the wave. However, occasionally the wave packets
triggered irreversible changes to the clouds, which transformed from closed
mesoscale cellular convection to open form. In this paper we use large eddy simulation (LES) to
examine the physical mechanisms that cause this transition. Specifically, we
examine whether the clearing of the cloud is due to (i) the wave causing
additional cloud-top entrainment of warm, dry air or (ii) whether the
additional condensation of liquid water onto the existing drops and the
subsequent formation of drizzle are the important mechanisms. We find that,
although the wave does cause additional drizzle formation, this is not the
reason for the persistent clearing of the cloud; rather it is the additional
entrainment of warm, dry air into the cloud followed by a reduction in
longwave cooling, although this only has a significant effect when the cloud
is starting to decouple from the boundary layer. The result in this case is
a change from a stratocumulus to a more patchy cloud regime. For the
simulations presented here, cloud condensation nuclei (CCN) scavenging did not play
an important role in the clearing of the cloud. The results have implications
for understanding transitions between the different cellular regimes in
marine boundary layer (MBL) clouds. |
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