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| Titel |
Cloud and boundary layer interactions over the Arctic sea ice in late summer |
| VerfasserIn |
M. D. Shupe, P. O. G. Persson, I. M. Brooks, M. Tjernström, J. Sedlar, T. Mauritsen, S. Sjogren, C. Leck |
| 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. 18 ; Nr. 13, no. 18 (2013-09-24), S.9379-9399 |
| Datensatznummer |
250085706
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| Publikation (Nr.) |
 copernicus.org/acp-13-9379-2013.pdf |
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| Zusammenfassung |
Observations from the Arctic Summer Cloud Ocean Study (ASCOS), in the
central Arctic sea-ice pack in late summer 2008, provide a detailed view of
cloud–atmosphere–surface interactions and vertical mixing processes over the
sea-ice environment. Measurements from a suite of ground-based remote
sensors, near-surface meteorological and aerosol instruments, and profiles
from radiosondes and a helicopter are combined to characterize a week-long
period dominated by low-level, mixed-phase, stratocumulus clouds. Detailed
case studies and statistical analyses are used to develop a conceptual model
for the cloud and atmosphere structure and their interactions in this
environment.
Clouds were persistent during the period of study, having qualities that
suggest they were sustained through a combination of advective influences
and in-cloud processes, with little contribution from the surface. Radiative
cooling near cloud top produced buoyancy-driven, turbulent eddies that
contributed to cloud formation and created a cloud-driven mixed layer. The
depth of this mixed layer was related to the amount of turbulence and
condensed cloud water. Coupling of this cloud-driven mixed layer to the
surface boundary layer was primarily determined by proximity. For 75% of
the period of study, the primary stratocumulus cloud-driven mixed layer was
decoupled from the surface and typically at a warmer potential temperature.
Since the near-surface temperature was constrained by the ocean–ice mixture,
warm temperatures aloft suggest that these air masses had not significantly
interacted with the sea-ice surface. Instead, back-trajectory analyses
suggest that these warm air masses advected into the central Arctic Basin
from lower latitudes. Moisture and aerosol particles likely accompanied
these air masses, providing necessary support for cloud formation. On the
occasions when cloud–surface coupling did occur, back trajectories indicated
that these air masses advected at low levels, while mixing processes kept
the mixed layer in equilibrium with the near-surface environment. Rather
than contributing buoyancy forcing for the mixed-layer dynamics, the surface
instead simply appeared to respond to the mixed-layer processes aloft.
Clouds in these cases often contained slightly higher condensed water
amounts, potentially due to additional moisture sources from below. |
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