资源环境科技发展态势分析平台

A commonly observed spectral feature of electromagnetic emissions stimulated by powerful radio waves in ionospheric plasma is found to have an exponential frequency spectrum. This so called broad upshifted maximum (BUM) is excited for pump frequencies near and slightly above an harmonic of the ionospheric electron gyro frequency. A simplified model of lower hybrid oscillations driven by parametric four-wave interaction localized in a cylindrical density depletion shows how the plasma drift can exhibit deterministic chaos. The associated exponential spectra are consistent with the experimental results.