Reflection of VLF radio waves at a junction in the Earth-ionosphere waveguide

The conditions for the neglect of reflection of VLF modes incident on a junction between the daytime and nighttime Earth-ionosphere waveguides are considered. It is shown that reflections are indeed small but some interesting and possibly significant exceptions may occur at highly oblique incidence. In fact, total reflection may take place for night-to-day transmission at angles within several degrees of grazing. The same analytical model is also relevant to oblique transmission across a flat lying coast line