Evolution of subkilometer scale ionospheric irregularities generated by high‐power HF waves

Abstract

Abstract. Electron density irregularities in the F region excited by the European incoherent scatter (EISCAT) high-power high-frequency (HF) facility in Ramfjordmoen, Norway, have been studied in detail by observing scintillations of 250-MHz satellite signals traversing the HF beam. Spaced antenna measurements were performed to determine the temporal structure of scintillation and the drift of the irregularities. Studies of scintillation spectra indicate that even though the onset occurs nearly simultaneously for all irregularity scale sizes, the electron density irregularities with wavelengths in the range of 50-15 m attain their saturation amplitudes within tens of seconds, whereas longer scale-size irregularities with wavelengths exceeding 100 m saturate in the timescale of minutes. The threshold power density requirement for the generation of irregularities of different scales has also been studied by the variation of the heater power. It is found that for large-scale (>100 m) irregularities the threshold power density varies inversely as the irregularity wavelength with a power law index of 4 as predicted by the theories of self-focusing instability.

Temporal evolution of pump beam self‐focusing at the High‐Frequency Active Auroral Research Program

“…Theory by Guzdar et al [1996] found that self-focusing favors large transverse scale sizes (>km) because diffraction effects suppress self-focusing at shorter wavelengths. Scintillation observations at EISCAT confirm this idea [Basu et al, 1997]. However, the growth time of km scale irregularities is minutes in contrast tens of seconds for 10 m scale irregularities and seconds for meter-scale irregularities [Basu et al, 1997].…”

“…Scintillation observations at EISCAT confirm this idea [Basu et al, 1997]. However, the growth time of km scale irregularities is minutes in contrast tens of seconds for 10 m scale irregularities and seconds for meter-scale irregularities [Basu et al, 1997].…”

On the location and structure of the artificial 630-nm airglow patch over Sura facility

“…Djuth et al, 2005). Such structures were also obtained by different radio methods and in-situ measurements (Basu et al, 1997;Kelley et al, 1995;Frolov et al, 2001;Myasnikov et al, 2001;Djuth et al, 2006). The existence of such structures is supported by theoretical predictions (e.g.…”

Kinetics of density striations excited by powerful electromagnetic waves in the ionosphere

“…The plasma density inside these striations is a few percent less than that of the ambient plasma. These plasma striations have a wide range of scales l Ќ across the geomagnetic field from a few decimeters 1 or less to meter scale 2,3 as obtained from radar scatter measurements, subkilometer scales as obtained from scintillation measurements of radio star and satellite signals, 4,5 up to more than a kilometer as obtained from comparing density fluctuations measured by satellite and radar plasma line fluctuations. 6 During pump beam self-focusing in high-latitude experiments, evidence of density striations with scales of a few kilometers across the geomagnetic field were observed in optical emissions during pumping in geomagnetic zenith.…”