This talk will combine stratospheric lidar observations and meteorological modelling to discuss and illustrate the complex structure of mesoscale mountain waves above Scandinanavia. At three successive days at the end of January 2000 the DLR airborne lidar OLEX explored mountain-wave-induced polar stratospheric clouds above the Scandinavian mountain ridge.

Depending on the synoptical-scale meteorological conditions stratospheric temperature anomalies of different amplitude and horizontal extent are generated by upward propagating mountain waves. Short-term excitation of about 6 hours resulted in localised stratospheric temperature anomalies directly above the mountain ridge. The lidar observations and the mesoscale modeling give evidence for wave breaking below a critical level at about 25 km altitude. In this case, the elevation of the observed clouds differed not much from the synoptic-scale clouds upstream above the Norwegian Sea. On the other hand, just one day later, long-lasting flow (more than 12 h) past the Scandinavian mountain ridge formed huge 400 km horizontally extending stratospheric ice clouds in altitudes as much as 5 km above the elevation of the upstream clouds. Inertia gravity waves with horizontal wavelengths of about 350 km are responsible for their formation. For the first time, a predicted temperature minimum due to the action of inertia gravity waves far downstream of the mountains could be proofed by the observation of an isolated stratospheric ice cloud above Finland.