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| Titel |
In-situ aircraft observations of ice concentrations within clouds over the Antarctic Peninsula and Larsen Ice Shelf |
| VerfasserIn |
D. P. Grosvenor, T. W. Choularton, T. Lachlan-Cope, M. W. Gallagher, J. Crosier, K. N. Bower, R. S. Ladkin, J. R. Dorsey |
| 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 ; 12, no. 23 ; Nr. 12, no. 23 (2012-12-03), S.11275-11294 |
| Datensatznummer |
250011629
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| Publikation (Nr.) |
 copernicus.org/acp-12-11275-2012.pdf |
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| Zusammenfassung |
In-situ aircraft observations of ice crystal concentrations in
Antarctic clouds are presented for the first time. Orographic, layer
and wave clouds around the Antarctic Peninsula and Larsen Ice shelf
regions were penetrated by the British Antarctic Survey's Twin Otter
aircraft, which was equipped with modern cloud physics probes. The
clouds studied were mostly in the free troposphere and hence ice
crystals blown from the surface are unlikely to have been a major
source for the ice phase. The temperature range covered by the
experiments was 0 to −21 °C. The clouds were found to contain
supercooled liquid water in most regions and at heterogeneous ice
formation temperatures ice crystal concentrations (60 s
averages) were often less than 0.07 l−1,
although values up to 0.22 l−1 were
observed. Estimates of observed aerosol concentrations were used as
input into the DeMott et al. (2010) ice nuclei (IN)
parameterisation. The observed ice crystal number concentrations were
generally in broad agreement with the IN predictions, although on the
whole the predicted values were higher. Possible reasons for this are
discussed and include the lack of IN observations in this region with
which to characterise the parameterisation, and/or problems in
relating ice concentration measurements to IN concentrations. Other IN
parameterisations significantly overestimated the number of ice
particles. Generally ice particle concentrations were much lower than
found in clouds in middle latitudes for a given temperature.
Higher ice crystal concentrations were sometimes observed at
temperatures warmer than −9 °C, with values of several per
litre reached. These were attributable to secondary ice particle
production by the Hallett Mossop process. Even in this temperature
range it was observed that there were regions with little or no ice
that were dominated by supercooled liquid water. It is likely that in
some cases this was due to a lack of seeding ice crystals to act as
rimers to initiate secondary ice particle production. This highlights
the chaotic and spatially inhomogeneous nature of this process and indicates that the accurate
representation of it in global models is likely to represent
a challenge. However, the contrast between Hallett Mossop zone ice
concentrations and the fairly low concentrations of heterogeneously
nucleated ice suggests that the Hallet Mossop process has the
potential to be very important in remote, pristine regions such as
around the Antarctic coast. |
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