VLF wave generation using VLF heating: a pointer to a new technique for ELF wave production?

The generation of very-low-frequency (VLF) waves via the cubic nonlinearity of the ionosphere using a VLF `heater´ at 16.4 kHz ±25 Hz (JXN Norway in FSK mode) and an adjacent `probe´ VLF transmitter (Omega Norway) on 12.1 kHz is reported. The transmitters are located near Mo I Rana, on the west coast of Norway. This experiment relies on what may be a unique configuration of these two VLF transmitters, in that they are separated on the Earth´s surface by less than half of their mean VLF wavelength. Their signals can thus be expected to interact in the ionosphere. Clear signals have been observed on 20.65 kHz and 20.75 kHz at Lycksele and Uppsala in Sweden, at a mean range of 330 and 760 km from the two VLF transmitters. It is believed that the signals are generated in the ionosphere above the VLF by the cubic nonlinearity mechanism. This mechanism may have possibilities for the generation of extra-low-frequency (ELF) waves from two adjacent VLF transmitters whose cubic nonlinearity difference frequency is in the ELF range. It is estimated that were Omega Norway to be retuned to an appropriate frequency (32.9 kHz) then the ionosphere above Aldra should simulate an ELF antenna with an output power of about 10 mW. VLF transmitters at lower magnetic latitudes, such as those operating in Hawaii, if suitably retuned may cause the ionosphere to radiate significantly more ELF energy, typically 10 W at 100 Hz