Radially Full Reflection of Fast Magnetosonic Waves Near the Cut-Off Frequency

Fast magnetosonic (MS) waves have been found to propagate mainly in the radial direction inside the plasmasphere. One main topic about the radial propagation of MS waves is whether they would propagate down to the ground or be reflected at some regions. Since WKB assumption might become invalid near the reflection point (if the reflection happens), an analytic approach has been utilized to investigate the propagation behavior of MS waves in this study. It is found that as MS waves propagate inward into the Earth, they might reach the cut-off regions when their frequencies become close to the cut-off frequency. Moreover, as demonstrated by our theoretical model, the behavior of MS waves around these regions can be described by the Airy's equation. Our results find that MS waves would be fully reflected near the cut-off point, since only evanescent waves are allowed in the cut-off regions.