Observational and modeling studies reveal that an appreciable fraction of mesospheric and lower thermospheric variability in space and time can be attributed to planetary waves. Measurements indicate that this is also true for summer conditions when vertically propagating stationary and travelling planetary waves experience strong attenuation in the lower part of the middle atmosphere. Possible causes including in-situ generation of normal modes are discussed.The methods of spherical 2-d turbulence analysis are used to investigate temporal and vertical changes of large-scale variability employing satellite radiance data. A relative increase of the variance related to intermediate-scale transient structures is found at high altitudes. This seems to reflect the special propagation conditions for travelling planetary waves at heights around the mesopause.