Parametric instability of VLF waves in the upper ionosphere

A parametric instability of quasi-monochromatic VLF waves in the upper ionosphere is considered. It is shown that the initial signal scatters into a low-frequency plasma wave and decays into low-frequency and ion-cyclotron waves most effectively. A parametric interaction between two whistlers and an ion-cyclotron wave is considered. The above processes may be responsible for excitation of the low-hybrid resonance in the ionosphere and magnetosphere of the earth.