Properties of the thermal narrow-continuum component in the spectrum of stimulated ionospheric emission

Abstract

We present the results of experimental studies of the properties of the thermal narrow-continuum component NC th of stimulated electromagnetic emission (SEE) of the ionosphere observed in a narrow region between the pump frequency and the downshifted maximum (DM). Spectral and dynamic characteristics of the NC th component are considered and the dependence of its properties on the frequency and power of the pumping wave as well as on the zenith angle of a high-power radio-wave beam in the geomagnetic-meridian plane is analyzed. It is proved that the NC th generation is determined by the thermal (resonant) parametric instability near the level of the upper-hybrid resonance for a high-power radio wave. New experimental data on the properties of the main DM thermal component in the spectrum of stimulated electromagnetic emission, which we used as the reference component in most measurements, are presented.

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

“…Firstly, on the basis of numerous measurements it can be stated that the most preferable frequency range for this purpose is 5-6 MHz, where, according to [4,43], the SEE components have the maximum intensity. In the range f PW ≈ 4.3-5 MHz, the intensity of the SEE components decreases with decreasing PW frequency.…”

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

“…The obtained new experimental data make it possible to refine the empirical models of generation of these SEE components as well as the degree of their interaction during the formation of the SEE spectrum. Detailed analysis of these data is outside the scope of the present paper and will be made in a separate publication [26].…”

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

“…1 and 2. These are the so-called broad continuum (BC) in the range of negative detunings ∆f from the pump-wave frequency f 0 for ∆f = f SEE − f 0 ∼ − kHz, the downshifted maximum (DM) at detunings ∆f ∼ − (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) kHz and its sidebands at multiple detunings (2DM, sometimes 3DM and 4DM), the narrow continuum (NC) at ∆f ∼ −(0-7) kHz, the upshifted maximum (UM) at ∆f ∼ 6-18 kHz, located almost symmetrically to the DM component with respect to the pump-wave frequency, and the broad upshifted maximum (BUM) at ∆f ∼ 15-150 kHz.…”

“…The ionospheric-heating experiments using the EISCAT (Tromsø, Norway), "Sura" (NIRFI, Russia), and HIPAS and HAARP (Alaska, USA) facilities are performed for 2 ≤ n ≤ 7. The dependence of the SEE spectra on the ratio between f 0 and nf ce was studied in [2][3][4][5][6][7][13][14][15][16][17][18][19][20]. At present, it can be considered a solid fact that, at least, for n = 3-7, the dependence of SEE spectral shapes on the quantity f 0 − nf ce are similar for different harmonic numbers n. As f 0 is varied between nf ce and (n + 1) f ce , five ranges of the pump-wave frequency in which the SEE spectra have different shapes can be distinguished: 1) the "resonant" range f 0 ≈ nf ce , in which the BC component is absent in the SEE spectrum, and the DM and BUM components have low intensities, 2) the "upshifted" range, in which the intense DM (often also 2DM and 3DM) and BUM components are present in the SEE spectrum, 3) the "strong-emission" range in which high-intensity DM and BC components as well as the BUS (Broad Upshifted Structure) component at ∆f ∼ 12-50 kHz are present in the SEE spectrum, 4) the "weak-emission" range, in which the BUS component disappears and the intensity of DM and BC components is significantly decreased, and 5) the "downshifted" range, in which the intensities of the DM component and also its sidebands and/or the BC component are again increased [3,5,7].…”