Reflection properties of the lower polar ionosphere, and the characteristics of VLF-wave excitation and propagation at high latitudes (Review)

Ionization sources and methods for the study of electron concentration in the lower polar ionosphere are examined. Sources of anomalous ionization are characterized, and results are presented concerning electron density in the lower polar ionosphere, measured by various methods. Attention is then given to VLF-wave propagation characteristics in the polar region. Transpolar VLF-wave propagation, local experiments, and magnetospheric and active experiments in the VLF range are discussed.