Long-term variation of the temperature of the middle atmosphere at mid-latitude: dynamical and radiative causes

International audienceTemperature of the middle atmosphere has been measured since 1979 at the Observatory of Haute-Provence (France, 44°N, 6°E) using the Rayleigh lidar technique. More than 500 temperature profiles in the height range 35-75 km have been used in that study. The main results are the following: temperature trends of opposite sign have been observed in the mesosphere (-20°K at 65 km) and in the stratosphere (+20°K at 40 km) between 1981 and 1985; but while the trend in the stratosphere is only found in winter, the tendency in the mesosphere is observed all year around. These temperature changes exhibit a highly significant correlation with the solar flux (represented by the radio flux at 10.7 cm) in the mesosphere and an equally significant anticorrelation in the winter stratosphere. On the other hand, the temperature at the 50-km level does not present any long-term variation. These results are interpreted as due to a superposition of a direct response of the mesosphere to the increase of the UV flux and a second effect, mainly present in winter, which affects all height ranges. This effect may or not be related to the 11-year solar cycle, but its height dependence and its sign can only be interpreted by a change in the planetary wave activity