A MECHANISM FOR GENERATING NONLINEAR ELECTRON-DENSITY DISTRIBUTIONS WHEN FORCED BY LARGE-AMPLITUDE MONOCHROMATIC GRAVITY-WAVES

Linear theory predicts that disturbances in the ionospheric electron d ensity field will closely resemble the characteristics of the forcing gravity wave. In this short note a simple mechanistic model which incl udes the effects of non-zero divergence of the nonlinear flux has been developed. The model indicates that higher frequency modes are genera ted when the gravity wave amplitude is sufficiently large. The harmoni cs can exhibit highly non-sinusoidal behaviour and this has implicatio ns for attempts to interpret medium-scale TIDs in terms of acoustic gr avity wave activity.