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Computer modelling of clouds at Kleiner Feldberg |
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| Authors: | R N Colvile R Sander T W Choularton K N Bower D W F Inglis W Wobrock D Schell I B Svenningsson A Wiedensohler H -C Hansson A Hallberg J A Ogren K J Noone M C Facchini S Fuzzi G Orsi B G Arends W Winiwarter T Schneider A Berner |
| Institution: | (1) Department of Pure & Applied Physics, UMIST, PO Box 88, M60 1QD Manchester, UK;(2) Air Chemistry Department, Max Planck Institut für Chemie, Mainz, Germany;(3) Department of Nuclear Physics, University of Lund, Sölvegatan 14, S-223 62 Lund, Sweden;(4) Department of Meteorology, Stockholm University, S-106 91 Stockholm, Sweden;(5) Zentrum für Umweltforschung and Institut für Meteorologie und Geophysik, Johann Wolfgang Goethe Universität, Robert Mayer Strasse, Frankfurt am Main, Germany;(6) Istituto FISBAT-C.N.R., Via de'Castagnoli 1, 40126 Bologna, Italy;(7) Netherlands Energy Research Foundation, PO Box 1, 1755 ZG Petten, The Netherlands;(8) Institut für Analytische Chemie, Technische Universität Wien, Getreidemarkt 9/151, A-1060 Vienna, Austria;(9) Deutsche Wetterdienst, Meteorologisches Observatorium Hamburg, Frahmredder 95, Hamburg, Germany;(10) Institut für Experimentalphysik, Universität Wien, Strudlhofgasse 4, A-1090 Vienna, Austria;(11) Present address: Laboratoire de Météorologie Physique, Université Blaise Pascal, 24 Avenue des Landais, 63177 Aubière Cedex, France;(12) Present address: NOAA/CMDL/R/E/CG, 325 Broadway, 80303-3328 Boulder, CO, USA;(13) Present address: Center for Atmospheric Chemistry Studies, Graduate School for Oceanography, 02882-1197 Narragansett, RI, USA;(14) Present address: Presidio Multizonale di Prevenzione, Settore Chimico, Via Triachini 17, 40138 Bologna, Italy;(15) Present address: Forschungzentrum Scibersdorf, A-2444 Selbersdorf, Austria |
| Abstract: | The airflow, cloud microphysics and gas- and aqueous-phase chemistry on Kleiner Feldberg have been modelled for the case study of the evening of 1 November 1990, in order to calculate parameters that are not easily measured in the cloud and thus to aid the interpretation of the GCE experimental data-set. An airflow model has been used to produce the updraught over complex terrain for the cloud model, with some care required to ensure realistic modelling of the strong stable stratification of the atmosphere. An extensive set of measurements has been made self-consistent and used to calculate gas and aerosol input parameters for the model. A typical run of the cloud model has calculated a peak supersaturation of 0.55% which occurs about 20 s after entering cloud where the updraught is 0.6 m s–1. This figure has been used to calculate the efficiency with which aerosol particles were scavenged; it is higher than that calculated by other methods, and produces a cloud with slightly too many droplets. A broad cloud droplet size spectrum has been produced by varying the model inputs to simulate turbulent mixing and fluctuations in cloud parameters in space and time, and the ability of mixing processes near cloud-base to produce a lower peak supersaturation is discussed. The scavenging of soluble gases by cloud droplets has been observed and departures from Henry's Law in bulk cloud-water samples seen to be caused by variation of pH across the droplet spectrum and the inability of diffusion to adjust initial distributions of highly soluble substances across the spectrum in the time available. Aqueous-phase chemistry has been found to play a minor role in the cloud as modelled, but circumstances in which these processes would be more important are identified. |
| Keywords: | Cloud model airflow model cloud chemistry cloud microphysics aerosols Henry's Law nitric acid cloud-water acidity turbulence mixing scavenging Kleiner Feldberg GCE |
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