High-power radio waves in the auroral ionosphere tend to further destabilize the linearly unstable electrostatic ion-cyclotron modes responsible for the long wavelength irregularities. The process is a four-wave parametric interaction involving a finite wave number pump, the ion-cyclotron modes, and two electrostatic sidebands. The nonlinear coupling arising through the ponderomotive force is sensitive to the wave vector of the pump k0. The growth rate falls off rapidly with increasing value of the low-frequency wave number k. ¿ American Geophysical Union 1988