抄録
The rate of energy penetration of VLF (10Kc) radio waves through a sharp ionospheric boundary under a constant magnetic field is calculated and the directions of the ray and the wave normal at the boundary are discussed.
For the case in which the VLF radio waves go up into the ionosphere from free space below, a rigorous calculation is performed using Bremmer's method and the existence of a quasi-Brewster's angle is ascertained.
In the case in which the waves come downwards from above, an approximate method is set up for the calculation and it is shown that the VLF waves can penetrate down to the earth's surface, only when the wave normal lies in a narrow band of angle near the normal of the boundary. In this case the ray direction of the penetrating waves is close to the magnetic field.
