Ionospheric Modification at Twice the Electron Cyclotron Frequency

Djuth, F. T.; Pedersen, T. R.; Gerken, E.; Bernhardt, P. A.; Selcher, C. A.; Bristow, W. A.; Kosch, M. J.

doi:10.1103/physrevlett.94.125001

Cited by 60 publications

(60 citation statements)

References 18 publications

(17 reference statements)

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“…Our result is consistent with the $1 -5 km scale size observed by Djuth et al [2005]. Since these observations are taken close to the magnetic field direction, no significant parallax is expected.…”

Section: Resultssupporting

confidence: 82%

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

et al. 2007

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[1] On 4 February 2005 the High-Frequency Active Auroral Research Program (HAARP) facility was operated at 2.85 MHz to produce artificial optical emissions in the ionosphere while passing through the second electron gyroharmonic. All-sky optical recordings were performed with 15 s integration, alternating between 557.7 and 630 nm. We report the first optical observations showing the temporal evolution of large-scale pump wave selffocusing in the magnetic zenith, observed in the 557.7 nm images. These clearly show that the maximum intensity was not reached after 15 s of pumping, which is unexpected since the emission delay time is <1 s, and that the optical signature had intensified in a much smaller region within the beam after 45 s of pumping. In addition, adjacent regions within the beam lost intensity. Radar measurements indicate a plasma depletion of $1% near the HF reflection altitude. Ray tracing of the pump wave through the plasma depletion region, which forms a concave reflecting radio wave mirror, reproduces the optical spatial morphology. A radio wave flux density gain of up to $30 dB may occur. In addition, the ray trace is consistent with the observed artificial optical emissions for critical plasma frequencies down to $0.5 MHz below the pump frequency.

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Section: Resultssupporting

confidence: 82%

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

et al. 2007

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“…2). Similar structures were observed in optical observations by Djuth et al (2005) at HAARP and Sentman (private communications) at HIPAS. The field-aligned optical enhancements exist due to the enhanced density of the O( 1 D), and therefore inhomogeneities also exist in the spatial distribution of suprathermal electrons.…”

Section: Mid-scale Field-aligned Structures In the Patchessupporting

confidence: 65%

“…In some experiments mid-scale (∼1 km) magnetic field-aligned structures in the HF pumped ionosphere are seen in the optical images (see, e.g. 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).…”

Section: Introductionmentioning

confidence: 96%

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

et al. 2007

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Abstract.Results are presented of the artificial optical emission of the atomic oxygen red line (the radiation of level O( 1 D) with a wavelength of 630 nm) from the HF-pumped ionosphere, obtained in September 2004 at the SURA heating facility situated near Nizhny Novgorod, Russia. For vertical pumping the airglow patch was increasingly displaced to the north, up to 7-8 • , with increasing reflection altitude. For large brightness of the emission, the airglow patch started to develop at the northern edge of the pump beam and later expanded to the south. These effects are attributed to the precipitation of supra-thermal electrons from the pump wave upper hybrid resonance altitude to lower altitudes where excitation of the O( 1 D) level is more effective due to the larger density of atomic oxygen, and the O( 1 D) lifetime is shorter. For a pump beam inclination of 12 • to the south, the optical spot was displaced by 4-5 • to the south relative to the straight-line projection of the pump beam onto the sky. This exceeds that expected from the ray tracing and may be related, most probably, to the so-called "magnetic zenith" effect. In addition, mid-scale (1-10 km) magnetic field-aligned structures were observed in the pumped volume of the ionosphere. The east-west motions of the airglow patches are also analyzed.

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“…HF-excited airglow enhancements were first reported at 630.0 nm (Sipler and Biondi, 1972) where they are most easily seen, but they can be and are found in HF experiments, due to both thermal and accelerated electrons (Carlson, 2002 suprathermal electrons. These suprathermal electrons produce enhanced optical emissions at 557.7 (Bernhardt et al, 1989;Pedersen et al, 2003), 777.4 (Carlson, 2002Djuth et al, 2005), 844.6 (Gustavsson et al, 2005), 427.8 (Holma et al, 2006), 660.0 (Djuth et al, 1999) which can complement thermal excitation of 630.0 nm optical emissions (Carlson, 2002), and are also seen directly in enhanced incoherent scatter radar plasma lines (Carlson et al, 1982).…”

Section: Discussionmentioning

confidence: 99%

Phenomena induced by powerful HF pumping towards magnetic zenith with a frequency near the F-region critical frequency and the third electron gyro harmonic frequency

Blagoveshchenskaya

Carlson²,

Kornienko

et al. 2009

Ann. Geophys.

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Abstract. Multi-instrument observational data from an experiment on 13 October 2006 at the EISCAT/HEATING facility at Tromsø, Norway are analysed. The experiment was carried out in the evening hours when the electron density in the F-region dropped, and the HF pump frequency f H was near and then above the critical frequency of the F2 layer. The distinctive feature of this experiment is that the pump frequency was just below the third electron gyro harmonic frequency, while both the HF pump beam and UHF radar beam were directed towards the magnetic zenith (MZ). The HF pump-induced phenomena were diagnosed with several instruments: the bi-static HF radio scatter on the LondonTromsø-St. Petersburg path, the CUTLASS radar in Hankasalmi (Finland), the European Incoherent Scatter (EIS-CAT) UHF radar at Tromsø and the Tromsø ionosonde (dynasonde). The results show thermal electron excitation of the HF-induced striations seen simultaneously from HF bi-static scatter and CUTLASS radar observations, accompanied by increases of electron temperature when the heater frequency was near and then above the critical frequency of the F2 layer by up to 0.4 MHz. An increase of the electron density up to 25% accompanied by strong HF-induced electron heating was observed, only when the heater frequency was near the critical frequency and just below the third electron gyro harmonic frequency. It is concluded that the combined effect of upper hybrid resonance and gyro resonance at the same altitude gives rise to strong electron heating, the excitation of Correspondence to: N. F. Blagoveshchenskaya (nataly@aari.nw.ru) striations, HF ray trapping and extension of HF waves to altitudes where they can excite Langmuir turbulence and fluxes of electrons accelerated to energies that produce ionization.

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Ionospheric Modification at Twice the Electron Cyclotron Frequency

Cited by 60 publications

References 18 publications

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

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

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

Phenomena induced by powerful HF pumping towards magnetic zenith with a frequency near the F-region critical frequency and the third electron gyro harmonic frequency

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