Atmos. Chem. Phys. Discuss., 3, 1557-1578, 2003
www.atmos-chem-phys-discuss.net/3/1557/2003/
doi:10.5194/acpd-3-1557-2003
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Ultrathin Tropical Tropopause Clouds (UTTCs): I. Cloud morphology and occurrence
T. Peter1, B. P. Luo1, H. Wernli1, M. Wirth2, C. Kiemle2, H. Flentje2, V. A. Yushkov3, V. Khattatov3, V. Rudakov3, A. Thomas4, S. Borrmann4, G. Toci5, P. Mazzinghi6, J. Beuermann7, C. Schiller7, F. Cairo8, G. Di Don-francesco9, P. Mazzinghi6, J. Beuermann7, C. Schiller7, F. Cairo8, G. Di Don-francesco9, A. Adriani8, C. M. Volk10, J. Strom11, K. Noone12, V. Mitev13, R. A. MacKenzie14, K. S. Carslaw15, T. Trautmann16, V. Santacesaria17, and L. Stefanutti18
1Institute for Atmospheric and Climate Science, ETH Zürich, Switzerland
2Institute for Atmospheric Physics, DLR Oberpfaffenhofen, Germany
3Central Aerological Observatory, Moscow, Russia
4Institute for Atmospheric Physics, University of Mainz, Germany
5Quantum Electronics Institute, National Research Council (IEQ-CNR), Florence, Italy
6National Institute of Applied Optics, Florence, Italy
7Institute I: Stratosphere, Forschungszentrum Jülich GmbH, Jülich, Germany
8Institute for Atmospheric Science and Climate, CNR, Roma, Italy
9ENEA Casaccia, Roma, Italy
10Institut für Meteorologie und Geophysik, Universität Frankfurt, Germany
11Institute of Applied Environmental Research, Stockholm University, Sweden
12Department of Meteorology, Stockholm University, Sweden
13Observatoire Cantonal, Neuchâtel, Switzerland
14Environmental Science Department, Lancaster University, UK
15School of the Environment, University of Leeds, UK
16Institute of Meteorology, University of Leipzig, Germany
17IROE – CNR “Nello Carrara", Firenze, Italy
18Geophysica-GEIE – CNR, Firenze, Italy

Abstract. Subvisible cirrus clouds (SVCs) may contribute to dehydration close to the tropical tropopause. The higher and colder SVCs and the larger their ice crystals, the more likely they represent the last efficient point of contact of the gas phase with the ice phase and, hence, the last dehydrating step, before the air enters the stratosphere. The first simultaneous in situ and remote sensing measurements of SVCs were taken during the APE-THESEO campaign in the western Indian ocean in February/March 1999. The observed clouds, termed Ultrathin Tropical Tropopause Clouds (UTTCs), belong to the geometrically and optically thinnest large-scale clouds in the Earth's atmosphere. Individual UTTCs may exist for many hours as an only 200–300 m thick cloud layer just a few hundred meters below the tropical cold point tropopause, covering up to 105 km2. With temperatures as low as 181 K these clouds are prime representatives for defining the water mixing ratio of air entering the lower stratosphere.

Citation: Peter, T., Luo, B. P., Wernli, H., Wirth, M., Kiemle, C., Flentje, H., Yushkov, V. A., Khattatov, V., Rudakov, V., Thomas, A., Borrmann, S., Toci, G., Mazzinghi, P., Beuermann, J., Schiller, C., Cairo, F., Di Don-francesco, G., Mazzinghi, P., Beuermann, J., Schiller, C., Cairo, F., Di Don-francesco, G., Adriani, A., Volk, C. M., Strom, J., Noone, K., Mitev, V., MacKenzie, R. A., Carslaw, K. S., Trautmann, T., Santacesaria, V., and Stefanutti, L.: Ultrathin Tropical Tropopause Clouds (UTTCs): I. Cloud morphology and occurrence, Atmos. Chem. Phys. Discuss., 3, 1557-1578, doi:10.5194/acpd-3-1557-2003, 2003.
 
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