RAY-TRACING STUDY OF THE PLASMAPAUSE EFFECT ON NON-DUCTED WHISTLER-MODE WAVE-PROPAGATION

The effect of the plasmapause on whistler-mode wave propagation and generation is investigated by means of the two-dimensional ray tracings started at the equator over a wide frequency range, 0.1 < LAMBDA-0 < 1.0 (LAMBDA-0 : wave frequency normalized by the equatorial gyrofrequency) and for a wide range of the initial wave normal angle theta-0. The main important findings are summarized as follows: (1) efficient gradient trapping is recognized at the inner edge of the plasmapause (especially with strong gradient) for lower frequency (LAMBDA-0 < 0.4) waves with smaller initial theta-0S (-40-degrees approximately + 40-degrees) generated at the equator; (2) lower frequency waves generated at the equator inside the plasmapause are found to have an access to low-altitude satellites and to ground, and their transmission latitude is slightly smaller than the plasmapause location; and (3) the outer edge of the plasmapause (especially with weak gradient) is also found to act as a guide for higher frequency (LAMBDA-0 > 0.5) waves. These theoretical findings are discussed with their relevance to the experimental facts of different magnetospheric whistler-mode emissions.