New results of investigations of nonlinear phenomena in the ionosphere

On the effects observed during modification of the earth’s upper ionosphere by high-power short radio pulses

“…From a comparison of the experimental results for T p = 1 and 10 s it follows that the time characteristics of fast processes agree only for the shortest PW-pulse durations. It can also be concluded that for τ p ≥ 0.5 s and T p = 10 s (or when the PW-pulse duration exceeds the development time τ RAA ≈ 0.3-0.5 s [15,19,23] of the rapid stage of anomalous attenuation and the average PW power P eff ≈ 0.3-0.5 MW [15,18,19] exceeds the threshold of thermal (resonant) parametric instability and ASSI generation), a significant variation in the properties of fast processes is observed, which is manifested as an abrupt increase in the characteristic time of the DSEE intensity maximum formation after the end of the PW pulse and as an enhancement of the role of the aftereffects leading to an increase in the time of recovery of the radiation intensity to the unperturbed state. In this case, a change in the properties of the DSEE intensity variations for τ p ≈ 0.5 s can be related to the fact that for smaller PW-pulse durations, the rapid stage of anomalous attenuation has no time to develop, and, as a consequence, an abrupt attenuation of the ASSI generation is observed.…”

“…On this basis, it should necessarily be assumed that, in this case, the governing factors are the duration and peak power of the action pulse rather than the average power of PW radiation. It should be noted that fast variations in the DSEE intensity must be determined not by the thermal (resonant) parametric instability in the PW-plasma interaction region, whose characteristic times exceed 0.3-0.5 s [15,18,19], but the rapidly developing processes observed at the stage of striction parametric instability near the reflection level of a high-power radio wave [20,21].…”

New Results of Studying the Lower Ionosphere by the Method of Resonance Scattering of Radio Waves from Artificial Periodic Inhomogeneities

“…Artificial periodic inhomogeneities (APIs) of the ionospheric plasma were detected for the first time in 1975 [1]. APIs are formed in the field of a high-power standing radio wave resulting from interference of the waves incident on the ionosphere and reflected from it.…”

Experimental Studies of the Effects Observed During the Nonlinear Interaction of Two High-Power Radio Waves in a Magnetoplasma

“…It was already noted that in the case of two-frequency heating of the ionospheric plasma, attenuation of the DM corresponding to the lower-frequency pump wave is always greater, which cannot be explained within the framework of the influence of ASIIs on the attenuation of the emission from the perturbed ionospheric region. In the latter case, on the contrary, higher-frequency waves undergo stronger absorption since their propagation path in the resonance-scattering region is longer [38]. Figure 7b also shows the results of measurements of the relative intensity I UM Σ /I UM DW of the UM component.…”

“…The large attenuation of the DM in the SEE spectrum for a lower pump frequency during the two-frequency heating and the attenuation of the BUM related to the lower-frequency PW are confirmed by other measurements and are typical of the studied phenomena. At the same time, it follows from the nature of the anomalous absorption of radio waves in the perturbed region of the ionosphere and from measurements of the absorption [38] that for f ≈ f PW , probe waves with a higher frequency are subject to the stronger absorption since these waves penetrate deeper into the perturbed region with developed small-scale irregularities and, hence, are more efficiently transformed into plasma oscillations. Thus, the measurement results again pose the question of the existence of other reasons for the DM and BUM attenuation during the two-frequency heating of the ionosphere, along with allowance for the influence of anomalous attenuation (due to ASIIs) on the intensity of the emission from the perturbed ionospheric region.…”