Climatology and trends of the middle atmospheric temperature (33–87 km) as seen by Rayleigh lidar over the south of France
Résumé
The technique of the Rayleigh lidar provides temperature profiles with a good temporal and vertical resolution in the middle atmosphere. Data obtained by 2 Rayleigh lidars set up at the Observatory of Haute-Provence (44°N, 6°E) and at Biscarrosse (44°N, 1°W) from 1978 to 1989 led to a unique set of data of 1200 night-mean temperature profiles from 37 to 87 km. A climatology of the temperature over the south of France has been established from this data base and new results concerning both the short-term and long-term variability of the middle atmosphere are presented in this paper. The observed temperature around 44°N, 0°W is in general colder than the mean temperature given in the COSPAR International Reference Atmosphere (1986) near 75 km and warmer above 80 km. A clear semi-annual variation is observed near 65 km with maxima occurring just after the equinoxes. The study of short-term variability indicates clearly two frequency domains: long periods below 65 km with a maximum in December-January which relate to planetary waves and shorter periods above 65 km induced by the breaking of gravity waves. A correlation with the 11-year solar cycle, negative in the stratosphere and positive in the mesosphere, is found to be well above the 95% confidence level with an amplitude larger in winter than in summer. However, with only 11 years of data it is obviously difficult to conclude that this atmospheric perturbation is induced by the solar forcing. A cooling of the mesosphere of about -4 K/decade at 60-70 km is found but is at the limit of the 95% confidence level, whereas we do not observe any significant trend in the stratosphere.
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