It is shown that finite amplitude electrostatic ion cyclotron (EIC) waves can parametrically decay into daughter EIC waves and kinetic Alfv¿n waves. Since the current associated with the latter is d.c. in the EIC time scale, it can linearly excite EIC waves when the amplitude of the Alfv¿n waves is sufficiently high. This provides a mechanism for the simultaneous existence of EIC and Alfv¿n fluctuations. Application of the theory in the auroral zone of the ionosphere is discussed.