Features of Excitation of Stimulated Electromagnetic Emission of the Ionosphere Modified by an Oblique High-Power Radio Wave

Abstract

We present the results of measuring the characteristics of the stimulated electromagnetic emission (SEE) of the ionosphere with variation in the zenith angle of a pump beam of high-power O-mode radio waves in the geomagnetic-meridian plane. The experiments were performed at the midlatitude heating facility "Sura." It is established that the maximum intensity of the DM and BC components of SEE is observed for southward inclination angles θ ≈ 8 • −−12 • of the antenna beam, for which the most intense generation of artificial small-scale ionospheric irregularities also takes place. Based on the results of measurements near the fourth and fifth harmonics of the electron gyrofrequency, it is found that the first component of the BUM (BUM-1) is generated only when the pump wave reaches the plasma-resonance region. This allows one to assume that, unlike the second component of the BUM (BUM-2), whose generation is determined by development of instability in the upper-hybrid resonance region, the BUM-1 generation mechanism should be related to processes of interaction between a high-power radio wave and the plasma in the plasma-resonance region.

Spectra of Stimulated Electromagnetic Emission of the Ionosphere Sweeping of the Pump Wave Frequency Near Gyroharmonics. II. Discussion of the Results

“…4 and 5 of our paper with respect to the region of BUM excitation differ from the conclusions of [45], according to which the BUM1 is excited in the region of pump-wave reflection for vertical pumping where f 0 ∼ f pe . Detailed analysis of the results of [45] is beyond the scope of this paper. However, it seems that the above-mentioned conclusion was drawn on the basis of experiments performed in the "cold start" regime.…”

Some results of measuring the characteristics of electromagnetic and plasma disturbances stimulated in the outer ionosphere by high-power high-frequency radio emission from the “Sura” facility

“…It is important that in session 2, the altitude of pump-wave reflection is about 230 km, which should impede the penetration of the disturbances of the plasma temperature and density to the outer ionosphere and exclude the possibility for the electrons, which were accelerated by plasma turbulence, to leave the zone of their generation because of the high density of the neutral ionosphere at such altitudes. Note that in both cases, the directional pattern of the facility was inclined by 12 • to the south in the plane of the geomagnetic meridian since the most intense excitation of artificial ionospheric turbulence is observed at these angles due to the magnetic-zenith effect [3,13]. Figure 1 shows the fragments of the satellite orbits projected onto the Earth's surface for sessions 1 (upper curve) and 2 (lower curve), in which the period of operation of the satellite-borne instruments in the burst mode is marked by bold lines.…”

On specific features of diurnal variations in characteristics of the diagnostic stimulated electromagnetic emission and their relation to the evolution of artificial ionospheric irregularities

“…The diagnostic emission was recorded at the frequency f = 5740 kHz (with the detuning ∆f − = 12 kHz, in the DM region). The directional diagram of the transmitting antenna was inclined southward by 10 • since the most intense generation of the thermal components of stimulated electromagnetic emission is observed at such angles [17]. Hereafter the times T in the tables correspond to the time of termination of the radiation of a high-power radio wave in the "carrier-frequency" regime and the transition to the regime of diagnostic-pulse radiation.…”