A Quest for a Controllable ULF Wave Source

Natural geomagnetic phenomena indicate that wave generation and amplification processes occur spontaneously in the magnetosphere and may be available under certain conditions to permit the frequency band near 1 Hz to be used for communications. An ionospheric duct provides low-loss propagation for waves in this band to distances of thousands of kilometers, and their large skin depth in seawater permits penetration to several hundred meters below the ocean surface. Several methods by which the generation of waves in this band might be possible are described. Methods involving the modulation of ionospheric conductivity include the injection of plasma clouds into the ionosphere and heating of the lower region with powerful radio transmitters. Methods involving nonlinear processes in the magnetosphere include cold plasma injection and very low frequency (VLF)/ultralow frequency (ULF) three-wave interactions.