The aim of this thesis is to determine which atmospheric conditions induce rotor formation in the surroundings of the city of Innsbruck, located in the Alpine Inn Valley, Austria. For this purpose, the impact of several idealized atmospheric conditions on the realistic terrain surrounding Innsbruck was investigated using numerical simulations. The Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) was used. The employed atmospheric conditions are favorable for southerly foehn and are derived from upstream radiosonde measurements. The presence of a rotor was diagnosed via characteristics of the wind field and a turbulence threshold.
The simulation results suggest, that southerly foehn in the Inn Valley can be accompanied by rotors under the condition that an inversion above the Alpine crest is present. The large scale wind direction can influence the probability for rotor formation. No rotors form if the upper level wind is south-westerly, since the mountain wave forcing is reduced. In contrast, south-easterly upper level wind is favorable for rotor formation, due to significant mountain wave activity. In the presence of an inversion, the strongest rotors develop in connection with trapped lee waves, developing due to strong vertical wind shear. Rotors developing in the surroundings of Innsbruck are spatially variable. The simulations show, that rotors are more likely to develop in the lee of peaks surrounding Innsbruck, where the mountain wave forcing is stronger, than over the city. High amplitude trapped lee waves leading to rotors over two kilometers in height, connected with extreme turbulence, can form close to Innsbruck airport.