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In situ measurements of tropical cloud properties in the West African Monsoon: upper tropospheric ice clouds, Mesoscale Convective System outflow, and subvisual cirrus

Frey, W. and Borrmann, S. and Kunkel, D. and Weigel, R. and de Reus, M. and Schlager, H. and Roiger, A. and Voigt, C. and Hoor, P. and Curtius, J. and Krämer, M. and Schiller, C. and Volk, C. M. and Homan, C. D. and Fierli, F. and Di Donfrancesco, G. and Ulanovsky, A. and Ravegnani, F. and Sitnikov, M.N. and Viciani, S. and D’Amato, F. and Shur, G. and Belyaev, D. and Law, K. S. and Cairo, F. (2011) In situ measurements of tropical cloud properties in the West African Monsoon: upper tropospheric ice clouds, Mesoscale Convective System outflow, and subvisual cirrus. Atmospheric Chemistry and Physics, 11, pp. 5569-5590. DOI: 10.5194/acp-11-5569-2011.

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Official URL: http://www.atmos-chem-phys.net/11/5569/2011/

Abstract

In situ measurements of ice crystal size distributions in tropical upper troposphere/lower stratosphere (UT/LS) clouds were performed during the SCOUT-AMMA campaign overWest 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 346K 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 1.5mm were found. A maximum ice water content of 0.05 gm−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 gm−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 gm−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.

Document Type:Article
Title:In situ measurements of tropical cloud properties in the West African Monsoon: upper tropospheric ice clouds, Mesoscale Convective System outflow, and subvisual cirrus
Authors:
AuthorsInstitution or Email of Authors
Frey, W.MPI für Chemie, Mainz
Borrmann, S.MPI für Chemie, Mainz
Kunkel, D.MPI für Chemie, Mainz
Weigel, R.Johannes Gutenberg Univ., Mainz
de Reus, M.Elementar Analysensysteme GmbH, Hanau
Schlager, H.DLR
Roiger, A.DLR
Voigt, C.Johannes Gutenberg Univ., Mainz/DLR
Hoor, P.Johannes Gutenberg Univ., Mainz
Curtius, J.Univ. Frankfurt
Krämer, M.FZ Jülich
Schiller, C.FZ Jülich
Volk, C. M. Univ. Wuppertal
Homan, C. D. Univ. Wuppertal
Fierli, F.ISAC-CNR, Rome, I
Di Donfrancesco, G.l’Energia e l’Ambiente, Frascati, I
Ulanovsky, A.ISTC, Dolgoprudny, Moskow Region, R
Ravegnani, F.ISAC-CNR, Rome, I
Sitnikov, M.N.ISTC, Dolgoprudny, Moskow Region, R
Viciani, S.CNR-INO, Florence, I
D’Amato, F.CNR-INO, Florence, I
Shur, G.ISTC, Dolgoprudny, Moskow Region, R
Belyaev, D.MDB, Moscow Region, R
Law, K. S.KNMI, De Bilt, NL
Cairo, F.ISAC-CNR, Rome, I
Date:2011
Journal or Publication Title:Atmospheric Chemistry and Physics
Refereed publication:Yes
In Open Access:Yes
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:11
DOI:10.5194/acp-11-5569-2011
Page Range:pp. 5569-5590
Status:Published
Keywords:ice crystal size distributions
HGF - Research field:Aeronautics, Space and Transport, Aeronautics, Space and Transport
HGF - Program:Space, Aeronautics
HGF - Program Themes:Earth Observation, ATM and Operation
DLR - Research area:Raumfahrt, Aeronautics
DLR - Program:R EO - Erdbeobachtung, L AO - Air Traffic Management and Operation
DLR - Research theme (Project):R - Vorhaben Atmosphären- und Klimaforschung, L - Climate, Weather and Environment
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics > Atmospheric Trace Species
Deposited By: Jana Freund
Deposited On:17 Nov 2011 15:33
Last Modified:26 Mar 2013 13:33

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