A CRITICAL EXAMINATION OF THE PRECIPITATION RECORDS AT THE PIC DU MIDI OBSERVATORY, PYRENEES, FRANCE

Abstract

The set of meteorological data collected from 1882 to 1984 at the Pic du Midi Observatory, a mountain station located at 2862 m MSL in the central part of the Pyrenees, includes precipitation measurements. It is well known that the quality of rain and snow precipitation measurements at a mountain station is poor. However, the new interest for all types of meteorological data at high elevation sites in relation with climatic changes leads to critically examine the precipitation data too. A homogeneity test of the Pic du Midi series, using a regional precipitation series in the surrounding plain of Aquitaine, confirms a warning made by the observers indicating that, since January 1937, the precipitation data may not be used. The test also suggests either not to use the data of the years 1923 to 1936, or to use them with a multiplying factor of 1.17. The data of the 1882–1922 period show that the precipitation amount at the Pic du Midi is nearly the same as in the surrounding valleys from May to November, but that it is about twice during the cold months. The seasonal and annual relationships between temperature and precipitation suggest that the increase in temperature observed from 1882 to 1984 at the Pic du Midi has resulted in a decrease in the winter and spring precipitation, but in no change in the summer and autumn precipitation.