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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 29, issue 5
Ann. Geophys., 29, 731–747, 2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 29, 731–747, 2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.

  03 May 2011

03 May 2011

Numerical study of tracers transport by a mesoscale convective system over West Africa

C. Barthe1, C. Mari2, J.-P. Chaboureau2, P. Tulet1,3, F. Roux2, and J.-P. Pinty2 C. Barthe et al.
  • 1Laboratoire de l'Atmosphère et des Cyclones, UMR8105, CNRS – Université de la Réunion and Météo-France, Saint-Denis, La Réunion, France
  • 2Laboratoire d'Aérologie, UMR5560, CNRS – Université de Toulouse, Toulouse, France
  • 3CNRM-GAME, URA1357, CNRS – Meteo-France, Toulouse, France

Abstract. A three-dimensional cloud-resolving model is used to investigate the vertical transport from the lower to the upper troposphere in a mesoscale convective system (MCS) that occurred over Niger on 15 August 2004. The redistribution of five passive tracers initially confined in horizontally homogeneous layers is analyzed. The monsoon layer tracer (0–1.5 km) is the most efficiently transported in the upper troposphere with concentrations 3 to 4 times higher than the other tracers in the anvil. On the contrary the African Easterly Jet tracer (~3 km) has the lowest contribution above 5 km. The vertical profiles of the mid-troposphere tracers (4.5–10 km) in the MCS exhibit two peaks: one in their initial layers, and the second one at 13–14 km altitude, underlying the importance of mid-tropospheric air in feeding the upper troposphere. Mid-tropospheric tracers also experience efficient transport by convective downdrafts with a consequent increase of their concentrations at the surface. The concentration of the upper troposphere–lower stratosphere tracer exhibits strong gradients at the edge of the cloud, meaning almost no entrainment of this tracer into the cloud. No downward transport from the upper troposphere is simulated below 5 km. A proxy for lightning produced NOx is transported preferentially in the forward anvil in the upper troposphere. Additionally, lateral inflows significantly contribute to the updraft and downdraft airflows emphasizing the three-dimensional structure of the West African MCSs.

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