Phase memory and additional memory in W. K. B. solutions for wave propagation in stratified media

Abstract

For a wave travelling obliquely in a stratified inhomogeneous medium the W. K. B. solution contains a phase memory term that expresses the cumulative change of complex phase as the wave propagates. This memory may have two parts. One is the familiar phase memory displayed in all cases. The other is an additional memory that has recently been shown to be important for radio waves in an anisotropic ionosphere, but it is not present for an isotropic ionosphere. The subject is examined here for some other types of wave in geophysics and atmospheric physics. It is shown that there can be an important additional memory for atmospheric acoustic gravity waves, and a small additional memory in some other cases including seismic waves when Coriolis force is allowed for, and electromagnetic waves in a stratified optically active but isotropic medium. For magnetohydrodynamic waves there is additional memory if a gravitational field is present, but not otherwise.