GROWTH OF PACKET OF FINITE AMPLITUDE VERY-LOW-FREQUENCY WAVES WITH SPECIAL REFERENCE TO MAGNETOSPHERE

Cyclotron resonance interaction of a packet of finite amplitude 'whistler' mode waves, travelling in the direction of the ambient magnetic field, with a collection of high energy electrons spiralling along the field is examined. It is concluded that when the amplitude of a packet of waves becomes large enough, the packet grows in length rather than amplitude. In a uniform medium a wave packet develops, in which the frequency varies monotonically along its length, approaching a quarter of the electron gyrofrequency at the front. The amplitude of the packet is more or less constant with distance along it. Using typical values of magnetosphere parameters, it is shown that, although the nonlinear effects considered should be important, a very-low-frequency wave packet in the magnetosphere is not likely to develop in the same way as for a similar uniform medium. © 1969.