Superlong Waves

Superlong Waves 

(also, myriametric waves), radio waves with wavelengths greater than 10 km (frequencies less than 30 kilohertz). Superlong waves have wavelengths comparable to the distance from the surface of the earth to the ionosphere; they can therefore propagate along the spherical earthionosphere waveguide over very long distances with negligible attenuation. Superlong waves are used in ground navigation systems. Under certain conditions, they can penetrate the ionosphere along the lines of force of the earth’s magnetic field and return to earth at the magnetically conjugate point in the opposite hemisphere (seeATMOSPHERICS). They also propagate in the earth’s crust and in the oceans and seas because the absorption coefficient in the conducting media is reduced as the frequency decreases. Thus, superlong waves can be used in underground and underwater communications systems (seeRADIO-WAVE PROPAGATION).