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1986 .

(2 publications)

L. Picon and M. Desbois. A method for measuring surface albedo variations from Meteosat images. Annales Geophysicae, 4:601-607, December 1986. [ bib | ADS link ]

This paper presents a preliminary work to estimate the variations of ground albedoes in Africa. The data are Meteosat images in visible and infrared channels for January and April 1982. The compositing of the images is used to approach at the best the clear sky conditions. These composite images can also help to detect the extension of the humid air penetration over Africa. The basic assumption is that at north of this area the atmospheric effects on the visible channel remained constant from one month to another. Then a simple histogram method is used for the comparison over the chosen areas between January and April in the visible channel. Only the effect on reflection of solar zenith angle has been taken into account.

K. Laval and L. Picon. Effect of a Change of the Surface Albedo of the Sahel on Climate. Journal of Atmospheric Sciences, 43:2418-2429, November 1986. [ bib | DOI | ADS link ]

We have investigated with our general circulation model the effect of an increase of surface albedo over the Sahel on climate. When albedo increases, the precipitation and evaporation rates are lower. Our experiment also has shown variations of zonal circulation over the Sahel: the Tropical Easterly Jet is stronger and easterlies at low altitude are weaker when the precipitation rate is higher. These results, in agreement with observations of the changes of circulation between dry and wet years, suggest that the albedo can play an important role in the triggering or the maintenance of a drought in the Sahel through the effects of circulation.

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