MIDLATITUDE LONG-TERM VARIABILITY OF THE MIDDLE ATMOSPHERE - TRENDS AND CYCLIC AND EPISODIC CHANGES

A study of variability and long-term trend detection in the middle atmosphere is performed using the temperature database obtained since 1979 by French Rayleigh lidars at 44 degrees N. A multivariable analysis is used to consider natural variability, including solar activity, quasi biennial oscillation (QBO), and volcanic eruption effects. As the solar proxy has an important role in this analysis, its choice is first discussed. Changes induced by solar activity reported here, mainly large negative correlation observed in the winter upper stratosphere, are not reproduced by numerical models without an unrealistic solar UV change. A significant warming of 6 K in the mesosphere is observed in summer 1992 and 1993. This large change could be due to aerosols injected in the stratosphere by the Mount Pinatubo eruption. Observed volcanic aerosol effects are compared with some numerical simulations and are shown to present some agreements. A long-term cooling of 0.4 K/year is observed in the mesosphere that is statistically significant but is larger than anthropogenic effects simulated in numerical models. In the upper stratosphere the small trend observed is not yet significant but in better agreement with model predictions.