Book Description
A terrestrial propagation model is studied where the earth to ionosphere waveguide system is cylindrically stratified, the dip angle of the static magnetic field is assumed to be arbitrary and the waves propagate in East to West or West to East directions at a constant magnetic latitude. The profiles of ionospheric electronic density chosen for the numerical computations are representative of sudden ionospheric disturbances (SID), solar flares, auroral absorption or polar cap absorption (PCA) events. The resulting phase velocity and attenuation rates of ELF and VLF signals are compared with those computed under representative quiet daytime conditions. PCA events (which give the most dramatic effects) cause a lowering of the effective ionosphere; the resulting propagation is nearly isotropic and the phase velocities are decreased at ELF and increased at VLF. The attenuation rates are increased at ELF and also in the lower part of the VLF band. The propagation parameters are affected to a lesser degree by the other events: ionospheric density perturbations at heights below 60 km have more readily discernable effects at ELF, while the changes of the ionospheric density gradient at larger heights are observable at VLF. However, these differences are not uniquely distinguishable from propagation characteristics obtainable under quiet daytime conditions. (Author).
