A novel method for the excitation of ELF waves in the ionospheres is presented. It utilizes the nonlinear mixing of two ground- or satellite-produced radio frequency waves with a compressional Alfv¿n wave. Parametric amplification thresholds are estimated to be between 10 and 20 MW peak power for 5-MHz pumps producing waves in the ELF range. Potential applications to ELF communications are discussed.