Channel probe observations of the auroral ionosphere during high‐power auroral stimulation heating experiments

Abstract

Perturbations of the bottomside auroral ionosphere caused by a high-power HF heater have been observed using a bistatically configured ionospheric channel probe. The heater transmitter power and antenna directivity resulted in a power density of the order of 1 mw/m2 at E layer heights and 0.2 mw/m 2 at F layer heights. O mode polarization was used for heating at a frequency of 2.85 MHz.Effects were observed at both E and F layer heights. The F layer effects consisted of enhanced attenuation, modified group delay at frequencies above and below the heater frequency, and a change in the character of the received signal from that of a time stable specular return to a time variable irregular return. All of these effects were most pronounced at frequencies closest to the heater frequency and diminished as the frequency deviated from the heater frequency. The formation of a localized heated cavity in the F layer is thought to be responsible for the observed changes in F layer signal group delay. Some form of parametric decay instability is thought to be responsible for the irregular character of the return signal during heating and for the enhanced attenuation which primarily affected the O mode of the probing signal. Heating induced Doppler effects were also noted in a second experiment. In particular, the main Doppler component exhibited a sharp change with the onset of heating followed by a steady change in Doppler from an initially large positive value to a large negative value at the time of heater shutdown. After heater shutdown the Doppler frequency relaxed to a steady value which differed from its preheating value. The spread of the Doppler return was also observed to broaden during heating which is consistent with the irregular character of the return during heating. The E layer return consisted of normal E layer echoes at frequencies below 2.5 MHz and of weak slant sporadic E echoes at and above 2.5 MHz. The slant sporadic E echoes were strongly attenuated during heating. An additional E layer effect involving what appears to be a localized, nonblanketing enhancement of foe was observed during heating. The most likely explanation for the enhanced attenuation of the slant sporadic E is E layer heating caused by energetic electron precipitation from the heated F layer. The enhanced fo E could also be attributed to high-energy electron precipitation from the F layer but direct ohmic heating of the E layer is an equally plausible explanation. 1407

Model simulation of the large-scale high-latitude F-layer modification by powerful HF waves with different modulation

“…In particular, four ionospheric heaters have been built in the latitudes of the auroral zone, namely, near Monchegorsk, Kola Peninsula; near Tromso, Scandinavia; near Fairbanks, Alaska; and near Gakona, Alaska. Many interesting scientific results have been obtained using these high-latitude heaters (Kapustin et al, 1977;Stubbe and Kopka, 1983;Warner et al, 1990;Rietveld et al, 1993 and references therein; Stubbe, 1996 and references therein; Rodriguez et al, 1998;Gustavsson et al, 2001;Rietveld et al, 2003;Djuth et al, 2004;Dhillon and Robinson, 2005;Mishin et al, 2005a;Ashrafi et al, 2006;Djuth et al, 2006;Kosch et al, 2007a). Initially, the ionospheric heaters were applied for the study of the lower ionosphere (D and E regions).…”

Spatial structure of plasma density perturbations, induced in the ionosphere modified by powerful HF radio waves: review of experimental results

“…[Богдан и др., 1980]) и стенд HIPAS (США, 1990 г. [Wagner et al, 1990]). Начиная с 1993 г. эксперименты по модификации ионосферы проводятся на наиболее мощном из построенных сегодня стендов HAARP (Аляска, США) [Gordon, 1997].…”

Asymmetric spectral broadening of modulated electrostatic ion‐cyclotron waves

“…Spectral broadening of magnetospheric waves and diagnostic signals has been observed in connection with artificial modification experiments in the Earth's ionosphere [Barry, 1974;Wagner et al, 1990]. The broadening is sometimes asymmetric.…”

“…One such mechanism involves the nearly resonant modulation of one or more plasma parameters that influence the dispersion of the magnetospheric wave of interest. Although no resonant modulation was deliberately applied in the above mentioned experiments, recent experiments at the HIPAS facility in Alaska have been performed in which the naturally occurring ionospheric current, or electrojet, is artificially modulated at frequencies in the ioncyclotron range using modulated HF power (Wong and Brandt, 1990;McCarrick et al, 1990).…”