Guidance of radio and hydromagnetic waves in the magnetosphere

Abstract

The strength and transverse scale of field-aligned irregularities of ionization likely to be required to guide electromagnetic waves through the magnetosphere around the lines of flux of the earth's magnetic field are investigated over the spectrum from hydromagnetic through audio to radio frequencies. For a given flux line there are about five decades of frequency over which guidance is possible for comparatively small fractional changes of ionization density. This frequency range slides down in frequency by about three decades as one moves from low- to high-latitude lines. Guidance disappears at sufficiently high radio frequencies because the magnetosphere then behaves substantially like free space. Guidance disappears at sufficiently low hydromagnetic frequencies because the transverse scale of the guiding structure required is too large to be accommodated in the magnetosphere. Guiding is unlikely much above 10 Mc/s or much below 1 cps.