A waveguide for low-frequency electromagnetic waves in the upper ionosphere

Abstract

New possibilities for extremely low frequency (ELF) radio communication are shown here to arise from the peculiar waveguide properties of the anisotropic multicomponent magnetoplasma in the upper ionosphere. Unlike the well known high-frequency (HF) communication channels formed by the electron density distribution in the lower ionosphere¹, the variable ionic composition and the geomagnetic field are essential for this spectral range below the ionic gyrofrequency. This global waveguide cavity, effective for Alfvèn wave propagation, surrounds the Earth near the ionospheric F₂-layer maximum. Unlike the LF waveguide cavity, located between the Earth's surface and the lower ionosphere², the aforesaid cavity is not connected with the boundaries of any media: the waveguide-like distribution of refractive index for Alfvèn waves is determined by smooth altitudinal profiles of electron and ionic densities. The dispersive properties of these waveguides are very sensitive to the proportions of heavy and light ions; therefore, they may be termed ‘chemical’ waveguides.