Journal Article

PreJuSER-17014

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png 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. ; Borrmann, S. ; Kunkel, D. ; Weigel, R. ; de Reus, M. ; Schlager, H. ; Roiger, A. ; Voigt, C. ; Hoor, P. ; Curtius, J. ; Krämer, M.FZJ* ; Schiller, C.FZJ* ; Volk, C. M. ; Homan, M. ; Fierli, F. ; Di Donfrancesco, G. ; Ulanovsky, A. ; Ravegnani, F. ; Sitnikov, N. M. ; Viciani, S. ; D'Amato, F. ; Shur, G. N. ; Belyaev, G. V. ; Law, K. S. ; Cairo, F.

2011
EGU Katlenburg-Lindau

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Please use a persistent id in citations: http://hdl.handle.net/2128/9964  doi:10.5194/acp-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 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 O-3 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 mu m. 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 2.3x10(-4) gm(-3), an effective radius of about 18 mu m, while the largest particles had a maximum dimension of 61 mu m.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 mu m, and the mean ice water content was about 1.4x10(-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.

Keyword(s): J ; m (auto)

Note: The SCOUT-O3 and SCOUT-AMMA projects were funded by the European Commission through Contract 505390-GOCE-CT-2004-505390 and the EC Integrated Projects AMMA-EU (Contract no. 004089-2). The M-55 Geophysica campaign was supported by the EEIG-Geophysica Consortium, CNRS-INSU, CNES, and EUFAR. Meteosat Second Generation data were provided by the AMMA database (http://aoc.amma-international.org/observation/satellite/) and were processed including the flight tracks by Sylwester Arabas from the University of Warsaw, Poland.Based on a French initiative, AMMA was built by an international scientific group and funded by a large number of agencies, especially from France, the United Kingdom, the United States, Africa, and - for us - German sources. It has been a beneficiary of a major financial contribution from the European Community Sixth Framework Programme (AMMA-EU). Significant financial support for our activities with the M-55 Geophysica in Australia and Burkina Faso also was supplied by the Max Planck Society.For the CIP data processing we gratefully acknowledge help from Aaron Bansemer (NCAR, Boulder, Co, USA). For very helpful comments on the manuscript we thank Jasmine Cetrone from the University of Washington, Seattle, USA. We thank Stefano Balestri, Ana Alfaro Martinez (ERS), and the pilots, engineers, crew of the M-55 Geophysica. The local authorities, scientists and staff in Ouagadougou (Burkina Faso) were wonderful hosts, and we thank for their amazing hospitality and support during this in many respects challenging campaign in Burkina Faso, which for all of us was a deeply moving life experience. Special thanks are due to Toro Drabo from the University in Ouagadougou. We grateful acknowledge the constructive and helpful comments by Darrel Baumgardner, Grant Allen, and the two anonymous referees.

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Contributing Institute(s):

1. Stratosphäre (IEK-7)

Research Program(s):

1. Atmosphäre und Klima (P23)

Appears in the scientific report 2011

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