Theoretical and Numerical Simulation Investigation of Parametric Processes Associated with Up-shifted Ionospheric Stimulated Radiation

Abstract

Stimulated Electromagnetic Emission SEE produced by heating the earth's ionosphere with high powered radiowaves is currently a topic of significant interest in ionospheric modification physics since it has tremendous potential as an ionospheric diagnostic tool. SEE is also a fundamental nonlinear process in plasma physics that is not currently well understood on a theoretical basis. SEE is believed to be produced by nonlinear wave-wave interactions involving the electromagnetic and electrostatic plasma waves in the altitude region where the pump wave frequency is near the upper hybrid resonance frequency. The most prominent up-shifted feature in the SEE spectrum is the broad up-shifted maximum BUM. From characteristics of this feature, a four-wave parametric decay process has been proposed as a viable mechanism for its production. The object of this work is to (1) investigate the nonlinear development of the four-wave decay instability by using theoretical and numerical simulation models and (2) access its possible role in the production of the BUM spectral feature. Results of this investigation show that there is good agreement between predictions of the proposed theoretical model and the numerical simulation experiments. The simulation frequency spectrum exhibits many of the important features of the experimental observations. The numerical results show that consideration of the full nonlinear development of the four-wave parametric instability is crucial in providing insight into the asymmetric nature of the wave frequency spectrum observed during the experiments.