Nonlinear generation of electromagnetic waves in a magnetoplasma

It is shown that a finite-amplitude upper-hybrid wave can decay into a perpendicularly (to an external magnetic field B0zˇ) propagating electrostatic lower-hybrid/ion-cyclotron wave and a left-handed circularly polarized (LHCP) electromagnetic wave (along B0) or an ordinary mode radiation (across B0). Nonlinear dispersion relations and the growth rates are obtained. It is suggested that the present nonlinear instability can be responsible for the enhanced narrow band radiation which is frequently observed in the Earth's magnetosphere.