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| Titel |
Satellite observations of cirrus clouds in the Northern Hemisphere lowermost stratosphere |
| VerfasserIn |
R. Spang, G. Günther, M. Riese, L. Hoffmann, R. Müller, S. Griessbach |
| 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 ; 15, no. 2 ; Nr. 15, no. 2 (2015-01-27), S.927-950 |
| Datensatznummer |
250119348
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| Publikation (Nr.) |
 copernicus.org/acp-15-927-2015.pdf |
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| Zusammenfassung |
Here we present observations of the Cryogenic Infrared Spectrometers and
Telescopes for the Atmosphere (CRISTA) of cirrus cloud and water vapour in
August 1997 in the upper troposphere and lower stratosphere (UTLS).
The observations indicate a considerable flux of moisture from the upper
tropical troposphere into the extratropical lowermost stratosphere (LMS),
resulting in the occurrence of high-altitude optically thin cirrus clouds in
the LMS.
The locations of the LMS cloud events observed by CRISTA are consistent with
the tropopause height determined from coinciding radiosonde data. For a
hemispheric analysis in tropopause relative coordinates an improved
tropopause determination has been applied to the European Centre for Medium-Range
Weather Forecasts (ECMWF) temperature profiles.
We found that a significant fraction of the cloud occurrences in the
tropopause region are located in the LMS, even if a conservative
overestimate of the cloud top height (CTH) determination by CRISTA of 500 m
is assumed. The results show rather high occurrence frequencies
(~ 5%) up to high northern latitudes (70° N) and
altitudes well above the tropopause (> 500 m at ~350 K and above) in large areas at mid- and high latitudes.
Comparisons with model runs of the Chemical Lagrangian Model of the
Stratosphere (CLaMS) over the CRISTA period show a reasonable consistency
in the retrieved cloud pattern. For this purpose a limb ray tracing
approach was applied through the 3-D model fields to obtain integrated
measurement information through the atmosphere along the limb path of the
instrument. The simplified cirrus scheme implemented in CLaMS seems to cause
a systematic underestimation in the CTH occurrence frequencies in the LMS
with respect to the observations. The observations together with the model
results demonstrate the importance of isentropic, quasi-horizontal transport
of water vapour from the subtropics and the potential for the occurrence of
cirrus clouds in the lowermost stratosphere and tropopause region. |
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