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| Titel |
In situ measurements of tropical cloud properties in the West African Monsoon: upper tropospheric ice clouds, Mesoscale Convective System outflow, and subvisual cirrus |
| VerfasserIn |
W. Frey, S. Borrmann, D. Kunkel, R. Weigel, M. Reus, H. Schlager, A. Roiger, C. Voigt, P. Hoor, J. Curtius, M. Krämer, C. Schiller, C. M. Volk, C. D. Homan, F. Fierli, G. Donfrancesco, A. Ulanovsky, F. Ravegnani, N. M. Sitnikov, S. Viciani, F. D'Amato, G. N. Shur, G. V. Belyaev, K. S. Law, F. Cairo |
| 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 ; 11, no. 12 ; Nr. 11, no. 12 (2011-06-16), S.5569-5590 |
| Datensatznummer |
250009846
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| Publikation (Nr.) |
 copernicus.org/acp-11-5569-2011.pdf |
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| Zusammenfassung |
In situ measurements of ice crystal size distributions in tropical
upper troposphere/lower stratosphere (UT/LS) clouds were performed during the
SCOUT-AMMA campaign over West Africa in August 2006. The cloud properties
were measured with a Forward Scattering Spectrometer Probe (FSSP-100) and a
Cloud Imaging Probe (CIP) operated aboard the Russian high altitude research
aircraft M-55 Geophysica with the mission base in Ouagadougou, Burkina Faso.
A total of 117 ice particle size distributions were obtained from the
measurements in the vicinity of Mesoscale Convective Systems (MCS). Two to
four modal lognormal size distributions were fitted to the average size
distributions for different potential temperature bins. The measurements
showed proportionately more large ice particles compared to former
measurements above maritime regions. With the help of trace gas measurements
of NO, NOy, CO2, CO, and O3 and
satellite images, clouds in young and aged MCS outflow were identified. These
events were observed at altitudes of 11.0 km to 14.2 km
corresponding to potential temperature levels of 346 K to
356 K. In a young outflow from a developing MCS ice crystal number
concentrations of up to (8.3 ± 1.6) cm−3 and rimed ice particles
with maximum dimensions exceeding 1.5 mm were found. A maximum ice
water content of 0.05 g m−3 was observed and an effective radius
of about 90 μm. In contrast the aged outflow events were more
diluted and showed a maximum number concentration of 0.03 cm−3, an
ice water content of 2.3 × 10−4 g m−3, an effective
radius of about 18 μm, while the largest particles had a maximum
dimension of 61 μm.
Close to the tropopause subvisual cirrus were encountered four times at
altitudes of 15 km to 16.4 km. The mean ice particle number
concentration of these encounters was 0.01 cm−3 with maximum
particle sizes of 130 μm, and the mean ice water content was about
1.4 × 10−4 g m−3. All known in situ
measurements of subvisual tropopause cirrus are compared and an exponential
fit on the size distributions is established for modelling purposes.
A
comparison of aerosol to ice crystal number concentrations, in order to
obtain an estimate on how many ice particles may result from activation of
the present aerosol, yielded low ratios for the subvisual cirrus cases of
roughly one cloud particle per 30 000 aerosol particles, while for the MCS
outflow cases this resulted in a high ratio of one cloud particle per 300
aerosol particles. |
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