Atmos. Chem. Phys. Discuss., 10, 4927-4961, 2010
© Author(s) 2010. This work is distributed
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Impact of deep convection in the tropical tropopause layer in West Africa: in-situ observations and mesoscale modelling
F. Fierli1, E. Orlandi1, K. S. Law2, C. Cagnazzo3, F. Cairo1, C. Schiller4, S. Borrmann5,6, G. Didonfrancesco7, F. Ravegnani1, and M. Volk8,9
1Institute for Atmospheric Sciences and Climate, ISAC-CNR, Italy
2LATMOS-IPSL, CNRS, Paris, France
3CMCC, Bologna, Italy
4Forschungzentrum Jülich, Jülich, Germany
5Max Planck Institute for Chemistry, Particle Chemistry Department, Mainz, Germany
6Institute for Atmospheric Physics, Johannes Gutenberg University, Mainz, Germany
7ENEA, ACS Dept., Rome, Italy
8Institute for Atmospheric and Environmental Sciences, J. W. Goethe-University, Frankfurt, Germany
9now at: Department of Physics, University of Wuppertal, Wuppertal, Germany

Abstract. We present the analysis of the impact of convection on the composition of the tropical tropopause layer region (TTL) in West-Africa during the AMMA-SCOUT campaign. Geophysica M55 aircraft observations of water vapor, ozone, aerosol and CO2 show perturbed values at altitudes ranging from 14 km to 17 km (above the main convective outflow) and satellite data indicates that air detrainment is likely originated from convective cloud east of the flight. Simulations of the BOLAM mesoscale model, nudged with infrared radiance temperatures, are used to estimate the convective impact in the upper troposphere and to assess the fraction of air processed by convection. The analysis shows that BOLAM correctly reproduces the location and the vertical structure of convective outflow. Model-aided analysis indicates that in the outflow of a large convective system, deep convection can largely modify chemical composition and aerosol distribution up to the tropical tropopause. Model analysis also shows that, on average, deep convection occurring in the entire Sahelian transect (up to 2000 km E of the measurement area) has a non negligible role in determining TTL composition.

Citation: Fierli, F., Orlandi, E., Law, K. S., Cagnazzo, C., Cairo, F., Schiller, C., Borrmann, S., Didonfrancesco, G., Ravegnani, F., and Volk, M.: Impact of deep convection in the tropical tropopause layer in West Africa: in-situ observations and mesoscale modelling, Atmos. Chem. Phys. Discuss., 10, 4927-4961, doi:10.5194/acpd-10-4927-2010, 2010.
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