Green's function for a switched plasma medium and a perturbation technique for the study of wave propagation in a transient plasma with a small rise time

摘要

Summary form only given. The main effect of switching a medium (creating a temporal discontinuity in the properties of a medium) is the splitting of the source (incident) wave into new waves whose frequencies are different. Lightning induced effects in the ionosphere cause a temporary enhancement of ionization. Such transient plasmas have a time-varying plasma frequency /spl omega//sub p/(t) with a rise time T/sub r/. If the period t/sub 0/ of a source wave existing before the transient effect begins is much larger than the rise time, the ionization change may be idealized as a sudden switching of the medium. The solution to this initial value problem with a step-change in the electron density profile is known and this profile will be considered as a reference profile. The switching action gives rise to a reflected wave (propagating in the opposite direction to that of the source wave) and a transmitted wave at an upshifted frequency /spl omega//sub 2/=(/spl omega//sub 0//sup 2/+/spl omega//sub p//sup p/). The topic of this paper is the solution of the initial value problem when t/sub 0/ is comparable to the rise time T/sub r/.