1986 .

(5 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.

J. Laurent, D. Brard, A. Girard, C. Camy-Peyret, C. Lippens, C. Muller, J. Vercheval, and M. Ackerman. Middle atmospheric water vapor observed by the Spacelab One grille spectrometer. Planetary and Space Science, 34:1067-1071, November 1986. [ bib | DOI | ADS link ]

Two water vapor atmospheric concentration profiles have been obtained, one at 33 deg N, 59 deg E, and the other at 68 deg S, 124 deg W, during the Spacelab One flight respectively on December 2 and 1, 1983. These profiles extend from the middle stratosphere up to mesopause and show significant differences above the altitude of 70 km, the Antarctic profile showing then higher concentrations. This result correlates with Spacelab One carbon monoxide observations and SME ozone results as far as the hydroxyl radical chemistry is concerned.

L. Fairhead, J.-E. Arlot, and W. Thuillot. An analysis of occultation observations of the Galilean satellites of Jupiter and comparison with theories. Astronomy Astrophysics, 169:360-366, November 1986. [ bib | ADS link ]

Historic occultation data on Galilean satellites were evaluated for usefulness for determining the proper motions of the satellites in conjunction with current, higher accuracy data. The database covers 4411 observations from 1836-1972 and includes observations from 44 different sites. The time residuals were calculated by two techniques which considered the time when the center of the satellite is on the conical surface resting on the planet with the apex on the earth. Errors were the same order of magnitude as obtained with visual eclipse data. Thus, the historic occultation data can be used in the same way as the historic eclipse data.

J. Vercheval, C. Lippens, C. Muller, M. Ackerman, and M.-P. Lemaitre. CO2 and CO vertical distribution in the middle atmosphere and lower thermosphere deduced from infrared spectra. Annales Geophysicae, 4:161-164, April 1986. [ bib | ADS link ]

The observation of infrared absorption lines by means of a grille spectrometer on board Spacelab 1 leads to the determination of CO2 and CO number densities in the low thermosphere and in the middle atmosphere. It is shown how the observational results can be represented by theoretical models based on the interaction processes between solar UV radiation, CO2, CO, and OH molecules.