Articles | Volume 3, issue 4
Atmos. Chem. Phys., 3, 1083–1091, 2003
https://doi.org/10.5194/acp-3-1083-2003
Atmos. Chem. Phys., 3, 1083–1091, 2003
https://doi.org/10.5194/acp-3-1083-2003

  29 Jul 2003

29 Jul 2003

Ultrathin Tropical Tropopause Clouds (UTTCs): I. Cloud morphology and occurrence

Th. Peter1, B. P. Luo1, 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 Donfrancesco9, A. Adriani8, C. M. Volk10, J. Strom11, K. Noone12, V. Mitev13, R. A. MacKenzie14, K. S. Carslaw15, T. Trautmann16, V. Santacesaria17, and L. Stefanutti18 Th. Peter et al.
  • 1Institute for Atmospheric and Climate Science, ETH Zürich, Switzerlands
  • 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, Switzerlandy, Sweden
  • 14Environmental Science Department, Lancaster University, UK
  • 15School of the Environment, University of Leeds, UKweden
  • 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.

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