PROPAGATION OF ELF AND VLF WAVES BELOW AN ANISOTROPIC IONOSPHERE WITH A DIPPING STATIC MAGNETIC FIELD.
SYLVANIA ELECTRONIC SYSTEMS-EAST WALTHAM MASS APPLIED RESEARCH LAB
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Fields of cylindrically curved ionosphere layers are approximated by exponential functions which consider the increase of the phase velocity and decrease of the attenuation rate with the altitude of the layers. Matrix multiplication techniques are applied to the treatment of multi-layer ionosphere models. The individual ionosphere layers are thin relative to the wavelength and the approximate field representations give in the limits of horizontal and radial static magnetic field results identical to those obtained using more accurate treatments of curvature effects. TM modes in the space between the earth and the ionosphere excite coupled TM and TE modes in the ionosphere layers, the presence of which are considered in an iterative solution of the modal equation. In the ELF range propagation parameters computed for the East to West EW and West to East WE directions differ most for dip angles of 15 to 30 degrees. In the VLF range propagation parameters may exhibit discontinuities for EW direction. The interference distance D of the two lower-wave guide modes is increased for propagation in the EW direction relative to propagation in WE direction provided that the electron density profiles exhibit sharp density gradients at heights in the range from 80 - 85 km. The desired propagation characteristics could not be produced in the presence of a nondipping static magnetic field or using smoothly varying electron density profiles. Author
- Radiofrequency Wave Propagation