HF Radio Wave Absorption in the Nighttime : Part III. Ray Paths and Absorption of MF and HF Radio Waves Incident at the Nighttime Ionosphere (Reports of the Japanese Antarctic Research Expedition)

Computations of the ray path and absorption of radio waves by means of the ray-tracing technique are applied to the oblique propagation of MF and HF waves passing through model ionospheres in the nighttime under different conditions. The field intensity deduced from those computed results is discussed in comparison with that measured on board the ship of the Japanese Antarctic Research Expeditions as already reported in Parts I and II of this paper. It is confirmed quantitatively to a certain degree that the ionization in the nighttime E region is responsible for the absorption of MF and lower HF waves.