The generation of ELF and VLF radio waves in the ionosphere using powerful hf transmitters

The generation of Extremely Low Frequency (ELF) and Very Low Frequency (VLF) waves by ionospheric heating using powerful High Frequency (HF) radio waves is reviewed. Most attention is given to natural current modulation using modulated HF heating and results are presented from all the major heating facilities in chronological order. Both around based and satellite measurements are described, as are techniques for enhancing ELF/VLF wave generation efficiency. Techniques for ELF/VLF wave generation which do not require the presence of natural ionospheric currents are also reviewed. (C) 1998 COSPAR. Published by Elsevier Science Ltd.