The Influence of Certain Ionoshperic Phenomena on Extremely Low Frequency (ELF) Propagation

A number of phenomena that may cause irregularities in extremely low frequency (ELF) ionospheric propagation are suggested. Geomagnetic anisotropy, path asymmetry due to different ionospheric characteristics on the darkened and sunlit hemispheres, effects of strong boundary discontinuities such as the twilight zone or northern latitude sporadic , and the effects of geophysical trauma such as solar particle fluxes are considered. A primitive analysis of ELF propagation data illustrates that an association can be drawn between the effects of solar charged particle emissions and coincident ELF propagation irregularities. Paths that pass through the auroral zone appear to be most severely affected.