FREQUENT SAHARAN DUST OUTBREAKS NORTH OF THE PYRENEES: A sign of a climatic change?

• Published in: Weather 1990, Vol.45 (9), p.327-333
• Main Authors: Dessens, J., Dinh, Pham Van
• Format: Article
• Language: English
• ISSN: 0043-1656; 1477-8696
• DOI: 10.1002/j.1477-8696.1990.tb05658.x

Examined is the possibility that the observed frequent and massive Saharan dust outbreaks with either dry or wet dustfalls on the ground in that part of France, immediately north of the Pyrenees range in the 7-year period 1983-1989, may be a sign of climate change. Described is a classical dust outbreak in southwestern France as illustrated by a specific instance at Lannemezan, Hautes-Pyrenees on June 23, 1988. A table presents a summary of observations of Saharan dust outbreaks at Lannemezan and of reports of dust falls in other parts of Europe in the period 1983-1988. Discussed are meteorological conditions for long-range transport of dust including the factors influencing long-range transport of dust such as the lifetime of dust particles and the horizontal wind velocity and turbulent mixing and precipitation; the determination of source areas of the dust clouds above Lannemezan by the computation of trajectories, and the meteorological conditions favorable to dust transport over southwestern France, as illustrated by a specific example. Possible effects of a dust increase in the atmosphere are summarized, viz., alteration in the radiation budget; decrease in air conductivity due to depletion of small ions by large concentrations of dust; change in the chemical content of rain; modification of cloud nucleation processes. It is concluded that frequent Saharan dust outbreaks have been observed since 1983 in southwestern France and the occurrence frequency has increased since 1986. Most of the events have concerned a much larger area than southwestern France so that they are probably the sign of a significant climatological change either in the synoptic flow or, more probably, in the source areas.