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| Titel |
A case study on the formation and evolution of ice supersaturation in the vicinity of a warm conveyor belt's outflow region |
| VerfasserIn |
P. Spichtinger, K. Gierens, H. Wernli |
| 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 ; 5, no. 4 ; Nr. 5, no. 4 (2005-03-22), S.973-987 |
| Datensatznummer |
250002664
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| Publikation (Nr.) |
 copernicus.org/acp-5-973-2005.pdf |
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| Zusammenfassung |
| A case study is presented on the formation and evolution of an
ice-supersaturated region (ISSR) that was detected by a radiosonde
in NE Germany at 06:00 UTC 29 November 2000. The ISSR was situated
in the vicinity of the outflow region of a warm conveyor belt
associated with an intense event of cyclogenesis in the eastern
North Atlantic. Using ECMWF analyses and trajectory calculations it
is determined when the air parcels became supersaturated and later
subsaturated again. In the case considered, the state of air parcel
supersaturation can last for longer than 24h. The ISSR was
unusually thick: while the mean vertical extension of ISSRs in NE
Germany is about 500m, the one investigated here reached 3km.
The ice-supersaturated region investigated was bordered both
vertically and horizontally by strongly subsaturated air. Near the
path of the radiosonde the ISSR was probably cloud free, as inferred
from METEOSAT infrared images. However, at other locations within
the ISSR it is probable that there were cirrus clouds. Relative
humidity measurements obtained by the Lindenberg radiosonde are used
to correct the negative bias of the ECMWF humidity and to construct
two-dimensional maps of ice supersaturation over Europe during the
considered period. A systematic backward trajectory analysis for the
ISSRs on these maps shows that the ISSR air masses themselves
experienced only a moderate upward motion during the previous days,
whereas parts of the ISSRs were located just above strongly
ascending air masses from the boundary layer. This indicates
qualitatively that warm conveyor belts associated with mid-latitude
cyclogenesis are disturbances that can induce the formation of ISSRs
in the upper troposphere. The ISSR maps also lead us to a new
perception of ISSRs as large dynamic regions of supersaturated air
where cirrus clouds can be embedded at some locations while there is
clear air at others. |
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