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

Th. Peter (1) , B. P. Luo (1) , M. Wirth (2) , C. Kiemle (2) , H. Flentje (2) , V. A. Yushkov (3) , V. Khattatov (3) , V. Rudakov (3) , A. Thomas (2) , S. Borrmann (2) , G. Toci (4) , P. Mazzinghi (5) , J. Beuermann (6) , C. Schiller (6) , F. Cairo (7) , G. Di Donfrancesco (8) , A. Adriani (7) , C. M. Volk (9) , J. Strom (10) , K. Noone (11) , V. Mitev (12) , R. A. Mackenzie (13) , K. S. Carslaw (14) , T. Trautmann (15) , V. Santacesaria (16) , L. Stefanutti (17)

1 IAC - Institute for Atmospheric and Climate Science [Zürich]
2 IPA - Institute for Atmospheric Physics [Mainz]
3 CAO - Central Aerological Observatory
4 Quantum Electronics Institute
5 National Institute of Applied Optics
6 Institute I: Stratosphere
7 ISAC - Istituto di Scienze dell'Atmosfera e del Clima
8 ENEA - Italian National agency for new technologies, Energy and sustainable economic development [Frascati]
9 Institut für Meteorologie und Geophysik [Frankfurt]
10 ITM - Institute of Applied Environmental Research [Stockholm]
11 MISU - Department of Meteorology [Stockholm]
12 OCN - Observatoire Cantonal de Neuchâtel
13 Department of Environmental Science [Lancaster]
14 SEE - School of Earth and Environment [Leeds]
15 Institute of Meteorology
16 IROE ? CNR "Nello Carrara"
17 Geophysica-GEIE ? "CNR"

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.

Domaines: Océan, Atmosphère

Th. Peter, B. P. Luo, M. Wirth, C. Kiemle, H. Flentje, et al.. Ultrathin Tropical Tropopause Clouds (UTTCs): I. Cloud morphology and occurrence. Atmospheric Chemistry and Physics, 2003, 3 (4), pp.1083-1091. ⟨hal-00295304⟩