Three Dimensional Propagation of Planetary Waves

Abstract

The ideas of ray tracing from geometrical optics and wave propagation in a slowly varying medium are used to study the propagation of plaentary waves in the atmosphere. Kinematic wave theory is applied to wave solutions of the linearised quasi-geostrophic potential vorticity equation on the sphere. An index is defined for planetary wave propagation in the vertical-meridional plane and it is shown that wave activity is refracted towards larger values of this index. Ray solutions for stationary planetary waves are calculated for simple basic states and for basic states representative of Northern Hemisphere summer, autumn and winter conditions. The results agree with those from observational and numerical model studies of stationary planetary waves in the atmosphere. It is shown that the sphericity of the Earth and the curvature of the zonal flow are important factors determining the propagation of planetary waves.