A model is presented to explain the nonresonant waves which give rise to the diffuse resonance onserved near 3/2 fH by the Alouette and Isis topside sounders, where fH is the ambient electron cyclotron frequency. These waves are the result of plasma wave instabilities driven ny anisotropic electron velocity distributions initiated by the high-power (400 W) short-duration (100 &mgr;s) sounder pulse. In a strictly linear analysis these instability-driven waves will decay owing to Landau damping on a time scale much shorter than the observed time duration of the diffuse resonance. Calculations of the nonlinear waveparticle coupling coefficients, however, indicate that the diffuse resonance wave can be maintained by nonlinear Landau damping of the sounder-stimulated 2fH wave. This 2fH wave is always observed with a time duration longer than that of the diffuse resonance wave, a finding which indicates that it is available as an energy source for the proposed nonlinear mechanism. The time duration of the diffuse resonance wave from the remote short-lived hot region back to the antenna. The model is consistent with the Alouette/Isis observations and clearly demonstrates the existence of nonlinear wave-particle interactions in the ionosphere. Such interactions have been observed in the laboratory and have long been speculated as being important in the energies of the earth's magnetosphere and ionosphere.