Clouds at the tropical tropopause: A case study during the APE-THESEO campaign over the western Indian Ocean

Vincenzo Santacesaria, Roberto Carla, Robert MacKenzie, Alberto Adriani, Francesco Cairo, Guido Didonfrancesco, Christoph Kiemle, Gianluca Redaelli, Jürgen Beuermann, Cornelius Schiller, Thomas Peter, Beiping Luo, Heini Wernli, Fabrizio Ravegnani, Alexey Ulanovsky, Vladimir Yushkov, Nikolay Sitnikov, Stefano Balestri, Leopoldo Stefanutti

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Abstract

In this paper, we report a detailed description of a thin cirrus at the tropopause above a cumulonimbus (Cb) convective cluster observed during the Airborne Platform for Earth Observation-Third European Stratospheric Experiment for Ozone (APE-THESEO) campaign in February-March 1999 in the western Indian Ocean. The thin cirrus (Ci) has an optical depth at 532 nm below 0.1, with extended subvisible stretches, and is located directly below the tropopause, which was supersaturated with respect to ice. A direct comparison between the optical depth retrieved by Meteosat and that obtained by means of the hygrometers installed on the M55-Geophysica aircraft is discussed showing discrepancies ranging from 10 to 20%. Combining satellite and aircraft data, we show that the observed Ci is not due to cirrus outflow from Cb anvils. In the absence of any deeply convective clouds reaching altitudes above 15 km, we propose a possible mechanism of Ci formation based on a net mesoscale transport of water vapor from altitudes above 16 km to the tropopause region around 18 km. This transport could be driven by the critical layer and turbulence induced by gravity waves that could have been generated by lower level Cb cluster activity. The proposed mechanism for high-altitude Ci formation corroborates the new paradigm of a tropical tropopause layer (TTL) or "substratosphere," several kilometers thick, which is decoupled from the convection-dominated lower troposphere.
Original languageEnglish
Pages (from-to)-
JournalJournal of Geophysical Research
Volume108
Issue number2
Publication statusPublished - 27 Jan 2003
Externally publishedYes

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All Science Journal Classification (ASJC) codes

  • Geophysics
  • Oceanography
  • Forestry
  • Aquatic Science
  • Ecology
  • Condensed Matter Physics
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Physical and Theoretical Chemistry
  • Polymers and Plastics
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Materials Chemistry
  • Palaeontology

Cite this

Santacesaria, V., Carla, R., MacKenzie, R., Adriani, A., Cairo, F., Didonfrancesco, G., ... Stefanutti, L. (2003). Clouds at the tropical tropopause: A case study during the APE-THESEO campaign over the western Indian Ocean. Journal of Geophysical Research, 108(2), -.