Direct conversion of ordinary mode into upper hybrid wave by density irregularities in the ionosphere

Abstract

We investigate direct conversion of ordinary mode into upper hybrid (UH) waves by pre‐existing electron density irregularities during ionospheric heating. The electric field amplitude and the average power absorbed by the excited UH waves are calculated when the irregularity distribution is (i) coherent, and (ii) incoherent with a broad band power spectrum modelled by a drift wave type scaling. For the typical parameters of the experiments, we find that the direct conversion process can be quite efficient.

Computer simulations for direct conversion of the HF electromagnetic wave into the upper hybrid wave in ionospheric heating experiments

“…Figure 9a shows essentially identical characteristics as Fig. 2 of the paper by Antani et al (1991) in which the parameters correspond to the real ionospheric conditions. We ®nd that the values of jijaji o j in Fig.…”

“…The maximum amplitude of the excited wave was recorded as 37% of the pump amplitude, under an optimum condition, that was found from the several simulation runs where we varied propagation angle of the pump wave, scale length of the density irregularity, degree of the irregularity, and thermal velocity of the plasma. The qualitative nature of the conversion fundamentally depends on the condition in the interaction region as predicted by theoretical work (Antani et al, 1991). The simulation resutls reveal, however, that the conversion eciency jijaji o j is much less than the prediction due to nonlinear eects.…”

“…For the ionospheric heating experiment, the following theoretical model has been given by Antani et al (1991). Figure 1 shows a schematic illustration of a typical ionospheric heating experiment.…”

“…The DC is basically a linear process and has no threshold, so that is dierent from a usual parametric process, and is distinct from the conventional linear mode conversion process that occurs independent of any plasma resonance such as cyclotron harmonics. The possibility of UH wave excitation by the DC in the ionospheric heating experiments was discussed theoretically by Antani et al (1991Antani et al ( , 1995. It is derived by the linear analysis that the amplitude of the excited UH wave is proportional to jhj À1 , where D is the dielectric function of the UH wave.…”

Modulation instability at the upper hybrid layer in high‐power radio wave ionospheric heating

“…It is well known that ordinary mode HF waves in high-power radio wave ionospheric heating can be converted into upper hybrid (UH) waves at the upper hybrid resonance height [Antani et al, 1991[Antani et al, , 1996. In addition, finite amplitude UH waves can be generated through direct mode conversion in the presence of We consider the evolution of a finite amplitude electrostatic upper hybrid wave generated near the upper hybrid resonance region.…”