Effect of phase-correlated electrons on whistler wavepacket propagation

The evolution of large-amplitude whistler wavepackets in a hot collisionless plasma is examined. When resonant electrons are trapped in the wave during a transit time, they acquire a correlation in phase of their perpendicular velocities relative to the local wave magnetic field, which causes new emissions and elongates the wavepacket in the direction of emergence of the resonant electrons. This is explained in terms of equations of propagation for the wavepacket amplitude, wavenumber, and frequency, involving phase correlated particles. The results of computer simulations showing the elongation of large-amplitude wavepackets, and the wavenumber and frequency characteristics of the new emission are presented.