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Volume 25, issue 11
Ann. Geophys., 25, 2271–2291, 2007
https://doi.org/10.5194/angeo-25-2271-2007
© Author(s) 2007. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 25, 2271–2291, 2007
https://doi.org/10.5194/angeo-25-2271-2007
© Author(s) 2007. This work is distributed under
the Creative Commons Attribution 3.0 License.

  29 Nov 2007

29 Nov 2007

Aerosol distribution over the western Mediterranean basin during a Tramontane/Mistral event

T. Salameh1, P. Drobinski2, L. Menut1, B. Bessagnet3, C. Flamant2, A. Hodzic4, and R. Vautard5 T. Salameh et al.
  • 1Institut Pierre Simon Laplace/Laboratoire de Météorologie Dynamique, École Polytechnique/ENS/UPMC/CNRS, Palaiseau, France
  • 2Institut Pierre Simon Laplace/Service d'Aéronomie, UPMC/UVSQ/CNRS, Paris, France
  • 3Institut National de l'Environnement Industriel et des Risques, INERIS, Verneuil en Halatte, France
  • 4National Center for Atmospheric Research, Boulder, CO, USA
  • 5Institut Pierre Simon Laplace/Laboratoire des Sciences du Climat et de l'Environnement, CEA/UVSQ/CNRS, Gif sur Yvette, France

Abstract. This paper investigates experimentally and numerically the time evolution of the spatial distribution of aerosols over the Western Mediterranean basin during the 24 March 1998 Mistral event documented during the FETCH experiment. Mistral and Tramontane are very frequently northerly wind storms (5–15 days per month) accelerated along the Rh\^one and Aude valleys (France) that can transport natural and anthropogenic aerosols offshore as far as a few hundred kilometers, which can, in turn, have an impact on the radiation budget over the Mediterranean Sea and on precipitation.

The spatial distribution of aerosols was documented by means of the airborne lidar LEANDRE-2 and space-borne radiometer SeaWIFS, and a validated mesoscale chemical simulation using the chemistry-transport model CHIMERE with an aerosol module, forced by the non-hydrostatic model MM5.

This study shows that: (1) the Mistral and Tramontane contribute to the offshore exportation of a large amount of aerosols originally emitted over continental Europe (in particular, ammonium nitrate in the particulate phase and sulfates) and along the shore from the industrialized and urban areas of Fos-Berre/Marseille. The amount of aerosol loading solely due to the Mistral and Tramontane is as large as 3–4 times the background aerosol amount and the contribution of sea-salt particles to the total aerosol loading and optical depth ranges from 1 to 10% even in such stormy conditions; (2) the aerosol concentration pattern is very unsteady as a result of the time evolution of the two winds (or Genoa cyclone position): The Tramontane wind prevails in the morning hours of 24 March, leaving room for the Mistral wind and an unusually strong Ligurian outflow in the afternoon. The Genoa surface low contributes to advect the aerosols along a cyclonic trajectory that skirts the North African coast and reaches Italy. The wakes trailing downstream the Massif Central and the Alps prevent any horizontal diffusion of the aerosols and can, at times, contribute to aerosol stagnation.

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