Nonlinear Processes in Geophysics www.nonlin-processes-geophys.net 1023-5809 1607-7946 12 4 2005 10.5194/npg-12-441-2005 http://www.nonlin-processes-geophys.net/12/441/2005/ http://www.nonlin-processes-geophys.net/12/441/2005/npg-12-441-2005.html http://www.nonlin-processes-geophys.net/12/441/2005/npg-12-441-2005.pdf 441 450 2005-04-07 Nonlinear compressional electromagnetic ion-cyclotron wavepackets in space plasmas I. Kourakis P. K. Shukla Institut für Theoretische Physik IV, Fakultät für Physik und Astronomie, Ruhr-Universität Bochum, 44780 Bochum, Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85740 Garching, Germany The parametric coupling between large amplitude magnetic field-aligned circularly polarized electromagnetic ion-cyclotron (EMIC) waves and ponderomotively driven ion-acoustic perturbations in magnetized space plasmas is considered. A cubic nonlinear Schrödinger equation for the modulated EMIC wave envelope is derived, and then solved analytically. The modulated EMIC waves are found to be stable (unstable) against ion-acoustic density perturbations, in the subsonic (supersonic, respectively) case, and they may propagate as "supersonic bright" (`"subsonic dark", i.e. "black" or "grey")type envelope solitons, i.e. electric field pulses (holes, voids),associated with (co-propagating) density humps. Explicit bright and dark (black/grey) envelope excitation profiles are presented, and the relevance of our investigation to space plasmas is discussed.