Theoretical analysis of lee waves over the Andes as seen by satellite pictures

Summary Satellite pictures have been utilised to detect mountain waves on the lee of the Andes range. The wavelengths as observed in the pictures from the distribution of clouds in parallel bands lie between 20 and 30 km for the five cases examined. The wavelengths have also been computed theoretically for these cases by an analytical method and a quasi-numerical method, using linearised perturbation equations. Wavelengths so computed are in fairly good agreement with the observed wavelengths, Vertical velocities associated with the waves along the different sectors of the Andes have also been computed. Their maximum values are of the order of 1–5 m sec^–1. Also, the quasi-stationary character of the waves, as noticed in some of the pictures, is discussed.