CROSS-MERIDIAN REFRACTION OF DUCTED WHISTLER-MODE WAVES

The propagation of a ducted whistler-mode wave is considered for the c ase in which the wave normal has an azimuthal component. The meridiona l gradient in electron density associated with the duct is taken to be sufficient to keep the meridional component of the wave normal close to the direction of the ambient magnetic field. Because of the strong anisotropy effects at whistler-mode frequencies, this may lead to a co nsiderable difference, even in cross-meridian propagation, from the un ducted case, where there is no such constraint. When there is axial sy mmetry, the deflection in longitude may be found by a series of elemen tary steps followed by quadrature, and results are presented for a dip ole magnetic field and realistic plasmaspheric density models. For the case of an azimuthal density gradient, a first-order theory is given in which the variation in longitude is given by quadrature, and result s are shown exhibiting the dependence on frequency and on the density model used. The case of a duct limited in longitude is also discussed. Here, the ray path oscillates in longitude, and a simple analysis ena bles the 'wavelength' and the relative amplitude of the oscillation to be estimated in terms of the density enhancement and the azimuthal wi dth of the duct. Finally, in an Appendix, the effects of the oscillati on in the meridional component of the wave normal, which are second-or der, are analysed.