  The properties of amplitude modulated broadband Alfven waves is investigated.
In particular, the dynamics of circularly polarized dispersive Alfven waves,
governed by a derivative nonlinear Schroedinger equation, is analyzed using the
Wigner formalism. The modulational instability of random phase dispersive pump
Alfven waves is investigated, and it is shown that the spectral broadening
gives rise to a new mode structure.

Plasma Physics