Filamentation instabilities of electron and ion cyclotron waves are investigated by taking into account electromagnetic wave driven stationary density ripples in a magnetized plasma. A general dispersion relation for the convective amplification of the radiation in a two-component electron-ion plasma is derived. Specific results for electron and ion cyclotron waves are presented. The relevance of our investigation to the ionosphere is pointed out. ¿ American Geophysical Union 1988