Cirrus clouds in convective outflow during the HIBISCUS campaign

F. Fierli (1) , G. Di Donfrancesco (2) , F. Cairo (1) , M. Zampieri (1, 3) , E. Orlandi (1)

1 ISAC - Istituto di Scienze dell'Atmosfera e del Clima
2 Ente Nazionale Energia e Ambiente
3 LMD - Laboratoire de Météorologie Dynamique (UMR 8539)

Light-weight microlidar measurements were taken on-board a stratospheric balloon during the HIBISCUS 2004 campaign, held in Bauru, Brazil (22 S, 49 W). Tropical cirrus observations showed high mesoscale variability in optical and microphysical properties. The cirrus clouds were observed throughout the flight between 12 and 15 km height. It was found that the clouds were composed of different layers, characterized by a marked variability in height, thickness and optical properties. Trajectory analysis and mesoscale transport simulations clearly revealed that the clouds had formed in the outflow of a large and persistent convective region, while the observed optical properties and cloud structure variability could be linked to different residence times of convective-processed air in the upper troposphere. Mesoscale simulations were able to reproduce the supersaturation due to recent outflow, while it was necessary to consider the presence of other formation processes than convective hydration for cirrus forming in aged detrained anvils.

Domaines: Océan, Atmosphère

F. Fierli, G. Di Donfrancesco, F. Cairo, M. Zampieri, E. Orlandi. Cirrus clouds in convective outflow during the HIBISCUS campaign. Atmospheric Chemistry and Physics Discussions, 2007, 7 (3), pp.6737-6765. ⟨hal-00328085⟩