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Browsing by Author "Cheng, K. T."

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    Numerical simulation of stimulated electromagnetic emissions in the ionosphere
    Cheng, K. T. (Virginia Tech, 1993-07-17)
    One-dimensional electrostatic plasma simulation using the particle-in-cell technique is used to study the spectral features of stimulated electromagnetic emission (SEE). SEE is a potential diagnostic tool to study the ionosphere and its spectrum provides a different view of the heated region from the incoherent scatter radar. At this time, a unified and complete theory which explains the SEE phenomena in detail does not exist. The SEE simulations we discuss are proposed to provide interpretation of many of the past puzzles of the experimental data, as well as to facilitate the design of future SEE experiments and the theoretical development of SEE. In the numerical simulation, only the upper hybrid layer where the geomagnetic field is essentially perpendicular to the density gradient is modelled. Three of the SEE features, namely the downshifted maximum (DM), upshifted maximum (UM) and broad upshifted maximum (BUM), are suggested to be generated at the upper hybrid layer. We observed these three features which have many similarities in the simulation. It is evident that the DM and UM are generated by the same parametric instability involving lower hybrid waves while the BUM is produced by other different mechanisms. Boundary effects are found important on the generation of all three features in the simulation. Moreover, detailed investigation of the simulation results raises a number of questions concerning detailed generation mechanisms of SEE which have not been considered and answered in the past. Besides the DM, UM and BUM features, the quenching of DM is also observed in the simulation when the pump frequency is very close to electron cyclotron harmonics. It is concluded that both the cyclotron damping and mode conversion of the upper hybrid wave into electron Bernstein modes are possible causes. Finally, some suggestions for the future SEE simulation are included.