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A. Bücher
and
J. Dessens

Abstract

Surface temperature was measured at the Pic du Midi de Bigorre, 2862 m MSL, from the foundation of the Observatory in 1878 until the closing of the meteorological station in 1984. After testing the homogeneity of the series with the annual mean temperatures in western Europe and in southwestern France, the period 1882–1970 was retained for trend analysis.

The mean annual temperature increased 0.83°C during the 89-yr period. This increase is the sum of a very significant increase in the daily minimum temperature (+ 2.11°C) and a decrease in the maximum temperature (− 0.45°C). In consequence, the most dramatic change in the temperature regime was the difference between maximum and minimum; this decreased from 8.05°C in 1882 to 5.49°C in 1970. A mean increase is observed in all seasons, but, as for western Europe, it is stronger in spring and fall than in winter and summer.

Analysis of cloudiness data for the same period shows a 15% increase in annual mean cloudiness and also significant year-to-year correlations between cloudiness and the maximum and minimum temperature. In consequence, the change in the temperature regime observed at the Pic du Midi since the end of last century is most probably the result of a climatic change involving an increase in cloud cover and, maybe, an increasing greenhouse effect.

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J. Bertrand
,
J. Baudet
, and
J. Dessens

Abstract

Atmospheric ice nuclei concentrations were measured at Abidjan for 27 months, with a mixing chamber operated at −20C. Seasonal variations appear to be linked to the position of the Intertropical Front. Air masses arriving from continental Africa correspond to high ice nuclei concentrations. The washing out of the atmosphere due to rain gives rise to low concentrations. The distribution of daily concentration averages may be represented by a log-normal distribution with high probability of convergence.

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