Trapping of whistler-waves through the side of ducts

It is shown that, when the whistler-mode phase refractive index is plotted along the length of geomagnetic field lines as a function of altitude, there is a minimum at an altitude of between 1400 and 2200 kms depending on magnetospheric model and wave frequency. Ray-tracing calculations are presented which show that the wave normal direction of upgoing whistler-mode waves can become field-aligned at and above the altitude of the refractive index minimum and this can lead to trapping of waves through the side of a suitably positioned duct. The mechanism is made possible by the increase of refractive index along the duct length above the altitude of the refractive index minimum. Ray paths resulting from trapping by this mechanism in both a winter night and a summer day model of the magnetospheric plasma are presented and discussed.

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