Ponderomotive narrow continuum (NC_p) component in stimulated electromagnetic emission spectra

Abstract

[1] We present experimental results concerning the ponderomotive narrow continuum (NC p ) in stimulated electromagnetic emission spectra, generated in the ionospheric F region plasma by a powerful O mode electromagnetic wave. It is found that the generation of the NC p is determined by the development of the parametric decay instability in the initial stage of the interaction of the HF pump wave with the plasma. The dependence of the NC p temporal and spectral characteristics on pump power, pump frequency, time of day, and pump schedule as well as its gyrofeatures are considered. A possible mechanism for the NC p generation is discussed.

Full-scale simulation study of stimulated electromagnetic emissions: The first ten milliseconds

“…The upshifted spectral components are considerably weaker. The spectra are very similar to the ponderomotive narrow continuum component in SEE spectra observed in experiment (Frolov et al 2004). It is interesting to further investigate the source of the downshifted components.…”

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

“…Taking all said above into account, it is reasonable to assume that in the case where the PW frequency is close to the gyroharmonic frequency and suppression of the thermal (resonant) parametric instability development and generation of small-scale artificial ionospheric irregularities is observed, the energy of a high-power radio wave, not undergoing a strong anomalous attenuation due to transformation of the pumping wave to upper-hybrid plasma oscillations, is transported to the level of PW reflection in the ionosphere at which strong excitation of the striction parametric instability becomes possible even in the regime of continuous radiation of a high-power radio wave and, as a consequence, NC p can be generated. It is important to emphasize that in the region of negative detunings, NC p is generated in the same frequency band as NC th and these components of radiation have similar spectral characteristics [9,20]. This explains why the attenuation of the radiation intensity in the region of the narrow-band SEE component is considerably smaller than that for DM since, instead of the suppressed component NC th , the component NC p , which is very similar to it, begins to be recorded.…”

“…(v) striction narrow-band radiation component, or ponderomotive narrow continuum NC p , which is observed for detunings of up to ∆f − ≈ 30−50 kHz at the stage of striction parametric instability development [8,9,16]; (vi) broadband radiation, which is similar to BUM and is detected in frequency ranges between the gyroharmonics, or broad upshifted structure (BUS) [19]. By tradition and to avoid therminological mess, we will use the above-mentioned English-language names of the radiation components.…”

“…According to the studies performed in the middle [3][4][5][6][7][8][9] and polar [1,[10][11][12][13][14] latitudes, the SEE in its stationary state, which is usually reached a few seconds (or a few tens of seconds) after the interaction begins, is a composition of more than ten separate spectral structures (radiation components), which is evidence for the variety of the plasma processes occurring simultaneously in the perturbed region (PR) of the ionosphere. An overview of the results obtained in these experiments is given in, e.g., [15][16][17].…”

“…This component is radiation without distinct structures, which is observed mainly at frequencies below the PW frequency and whose intensity, as a rule, exponentially decays with increase in the detuning ∆f − . Later on, after a more detailed study of its spectral and evolution characteristics [3,4,12,13], this component was divided into three components: NC p (fast narrow continuum, following the classification adopted in [16]), whose properties were studied in detail in [8,9,20], NC th (thermal narrow continuum, or, following [16], slow narrow continuum), and BC, whose properties were considered in detail in [3,4,16,17]. In what follows we consider the properties of the least explored thermal narrow-band component NC th , whose generaion is observed in a narrow region of detunings ∆f − ≤ 7 kHz between the frequencies f DM and f PW .…”