Planetary waves-mean flow interaction in the middle atmosphere: Lidar observations and modelisation

Lidar observations of the temperature from 30 to 80 km have been made at the Observatory of Haute-Provence on an operational basis since 1981. Data obtained during the four last winters indicate the quasi-systematic presence of traveling Rossby waves with periods ranging from 5 to 20 days and a vacillation of the zonal mean circulation leading to a succession of upper stratospheric warmings and associated mesospheric coolings spaced by 25 to 50 days. A semi-spectral model of the wave one-mean flow interaction has been used to interpret these results. When a stationary wave forcing is imposed at the lower boundary of the model, a vacillation of the zonal flow is obtained as soon as the amplitude of this wave reaches a critical value of about 140 m. When an 18-day westward traveling wave is imposed in supplement to this forcing, the date of occurrence of the upper stratospheric warmings is imposed by the coincidence of the phases of the two waves that enhanced the forcing.