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

Abstract

Alternative mechanisms of generation of the stimulated electromagnetic emission (SEE) excited in the ionosphere by high-power radio waves are analyzed on the basis of measurements of the SEE spectra obtained during the pump-wave frequency sweeping near the forth (n = 4) and fifth (n = 5) harmonics of the electron gyrofrequency nf ce [1] and their comparison with the existing physical models. A method for determination of the magnetic field strength and plasma density near the double-resonance region in the ionosphere is developed. It is shown that the generation of the broad upshifted maximum (BUM) feature in the SEE spectrum should occur several kilometers below the double-resonance altitude. A role of high-frequency plasma modes and small-scale magnetic field-aligned irregularities, excited under ionosphere pumping by a highpower radio wave, in the formation of SEE spectra is demonstrated. It is shown that the difference in the emission intensities for f 0 nf ce and f 0 > nf ce is related to different regions (altitudes) at which the plasma waves exist in these cases.

Spectra of Stimulated Electromagnetic Emission of the Ionosphere Upon Sweeping of the Pump Wave Frequency Near Gyroharmonics. I. Experimental Results

“…Detailed discussion of the physical processes responsible for the observed behavior of SEE spectra upon pumping-frequency variations in the vicinity of the electron gyroharmonics is given in the second part [26] of this paper. …”

“…The physical consequences of the obtained results are discussed in detail in the second part of this paper [26].…”

“…For small geomagnetic-field angles to the vertical direction (recall that the this angle is 18.5 • for the "Sura" facility) this scale is approximately equal to the altitude size of the perturbed ionosphere region and is comparable to the ionospheric-layer height. In this case, the DSEE is generated due to the excitation of upper-hybrid waves related to the diagnostic-wave scattering by field-aligned small-scale inhomogeneities near the level of its upper-hybrid resonance, where f DW ≈ f uh (see [26] for more detail). The altitudes of the upper-hybrid resonance for the diagnostic wave (and, hence, the diagnostic-wave frequency f DW ) and the pump-wave (and the frequency f 0 ) can significantly differ from each other, which allows one to diagnose the upper-hybrid turbulence at different altitudes in the perturbed region using the DSEE with different frequencies f DW [17].…”

Exploring HF‐induced ionospheric turbulence by Doppler sounding and stimulated electromagnetic emissions at the High Frequency Active Auroral Research Program heating facility

“…During the sweep, the pump frequency f 0 passes 4 f ce . This is indicated by the disappearance of the DM at f 0 ≈ 5581 ± 10 kHz and f DM ≈ 5573 ± 10 kHz (upsweep), implying that the double‐resonance condition f DM ≈ f UH ( z ) ≈ 4 f ce ( z ) [ Leyser et al ., ; Leyser , ; Carozzi et al ., ; Sergeev et al ., ; Grach et al ., ] is met at 5563–5583 kHz and f ce ( z ) ≈ 1393 ± 2.5 kHz. During the downsweep this occurs for f 0 ≈ 5565 ± 5 kHz and f DM ≈ 5556 ± 5 kHz.…”

Intermediate downshifted maximum of stimulated electromagnetic emission at high‐power HF heating: A new twist on an old problem

“…In particular, DM and its family (2DM, 3DM, etc. ), as well as UM, are understood in terms of a scenario including density striations δ n s and three‐wave interaction of upper hybrid and lower hybrid (LH) waves [ Leyser , ; Grach et al , ; Shvarts and Grach , ]. The primary UH waves (UH 1 ) appear via the thermal parametric instability and parametric decay instabilities of the O mode pump with frequencies and , respectively.…”