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

Santacesaria, V.; Stefanutti, L.; MacKenzie, R.; Luo, B.; Ulanovsky, A.; Yushkov, V.; Cario, F.; Kiemle, C.; Wernli, H.; Peter, T.; di Donfrancesco, G.; Carla, R.; Beuermann, J.; Balestri, S.; Adriani, A.; Schiller, C.; Ravegnani, F.; Redaelli, G.

doi:10.1029/2002JD002166

Journal Article

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

Santacesaria, V. ; Carla, R. ; MacKenzie, R. ; Adriani, A. ; Cario, F. ; di Donfrancesco, G. ; Kiemle, C. ; Redaelli, G. ; Beuermann, J.FZJ* ; Schiller, C.FZJ* ; Peter, T. ; Luo, B. ; Wernli, H. ; Ravegnani, F. ; Ulanovsky, A. ; Yushkov, V. ; Balestri, S. ; Stefanutti, L.

2003
Union Washington, DC

Journal of geophysical research / Atmospheres 108, 4044 (2003) [10.1029/2002JD002166]

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Please use a persistent id in citations: http://hdl.handle.net/2128/20879 doi:10.1029/2002JD002166

Abstract: [1] 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.

Keyword(s): J ; thin tropical cirrus (auto) ; APE-THESEO campaign (auto) ; tropical tropopause layer (TTL) (auto) ; convective system (auto)