Experimental and Numerical Studies on ELF/VLF Wave Generation by Amplitude-Modulated HF Heating Waves

Kuo, Spencer; Lee, S H; Bivolaru, Daniel; Kossey, Paul; Lee, M C; Riddolls, R.J.; Jastrzębski, Przemysław; Sentman, D. D.

doi:10.1238/physica.regular.067a00448

Cited by 16 publications

(18 citation statements)

References 23 publications

(24 reference statements)

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“…Measured dependence of the radiation intensity on the modulation frequency from a previous experiment by Kuo et al [2003] using the HAARP facility confirmed the results of the numerical model [ Kuo et al , 2002]. The experiment illustrated another important aspect of the numerical analysis.…”

Section: Introductionsupporting

confidence: 74%

“…The generation efficiency and signal quality are critical to practical applications. The generation efficiency varies with the modulation frequency [ Rietveld et al , 1989; Kuo et al , 2003], the mode type (O or X) and frequency of the HF heating wave, as well as the modulation scheme (i.e., waveform) [ Kuo et al , 1998, 2000, 2003] that also has an effect on the signal quality. Papadopoulos et al [1990] suggested a beam‐painting approach by enlarging the modulated region of the electrojet to enhance the ionospheric antenna gain.…”

Section: Introductionmentioning

confidence: 99%

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Determination of the height of the modulated electrojet region generating ELF radiation

Kuo¹,

Greco²

2007

Geophysical Research Letters

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[1] A virtual ionospheric antenna to generate ELF (extremely low frequency) waves is achievable by using amplitude modulated HF (high frequency) wave to modulate the electrojet current. The results of the numerical analysis show that the radiation intensities of ELF waves produced by modulated electrojet vary with the modulation frequency. Moreover, a ratio of two radiation intensities at two frequencies is height dependent. Thus, with the aid of the numerical results, the experimental measurements on the ratios of the radiation intensities of the ELF waves can provide unambiguous information on the height of the electrojet contributing to the ELF radiation. An experiment using the HAARP heating facility has been performed in 2005. The experimental results of three independent intensity ratios (25 Hz/205 Hz, 25 Hz/325 Hz, and 25 Hz/625 Hz) are used to demonstrate this new diagnostic technique. The height of the source region, where the modulated electrojet radiates most effectively, is determined to be between 94 Km and 97 Km. Citation: Kuo, S. P., and D. Greco (2007), Determination of the height of the modulated electrojet region generating ELF radiation, Geophys. Res. Lett., 34, L05103,

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Section: Introductionsupporting

confidence: 74%

Section: Introductionmentioning

confidence: 99%

Determination of the height of the modulated electrojet region generating ELF radiation

Kuo¹,

Greco²

2007

Geophysical Research Letters

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“…Thus, the electrojet current in the lower ionosphere can be modulated by an intensity modulated HF heating wave. Generation of ELF/VLF waves in the high latitude ionosphere via electrojet modulation has been studied experimentally [ Stubbe et al , 1981, 1985; Ferraro et al , 1982, 1984; James et al , 1984; Rietveld et al , 1986, 1989; Lee et al , 1990; McCarrick et al , 1990; Villasenor et al , 1996; Kuo et al , 2003; Kuo and Greco , 2007] and theoretically [ Stubbe et al , 1982; Papadopoulos and Chang , 1985; Papadopoulos et al , 1990; Kuo and Lee , 1993, 2004; Kuo et al , 1998, 2000, 2002].…”

Section: Introductionmentioning

confidence: 99%

VLF wave generation by amplitude‐modulated HF heater waves at Gakona, Alaska

Kuo¹,

Wu²,

Pradipta

et al. 2008

Geophysical Research Letters

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Experiments conducted at Gakona, Alaska, using the intensity‐modulated HF heating waves to interact with electrojet currents for the generation of VLF waves, are reported. An unexpected large increasing rate from 4 to 8 kHz in the frequency dependency of the VLF radiation intensity was observed. The peak value at 8 kHz was intense (about 7.5 dB above that of the 2 kHz signal used as a marker) and the wave intensity from 5 to 17 kHz appeared to be abnormally high (i.e., stronger than that at 2 kHz). In the experiments, we also observed the enhancement of spread‐E irregularities at electrojet current altitudes due to the amplitude‐modulated heater wave. These results and theoretical analyses suggest that temporally modulated electrojet currents mix with heater wave‐excited density irregularities to form whistler mode currents, which generate VLF whistler waves directly with much larger intensities and better directivity than a Hertzian dipole can.

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“…The induced alternating current (AC) in the electrojet is then the antenna current for VLF radiation at the modulation frequency and its harmonics. Generation of VLF waves in the high latitude ionosphere via electrojet modulation has been studied experimentally [1][2][3][4][5][6][7][8][9][10][11][12][13] and theoretically. [12][13][14][15][16][17][18][19][20][21][22] The heating and cooling rates as well as the available heating and cooling times in one modulation period affect the efficacy of conductivity modulation by an intensity modulated HF heater.…”

Section: Introductionmentioning

confidence: 99%

Ionospheric very low frequency transmitter

Kuo

2015

Physics of Plasmas

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The theme of this paper is to establish a reliable ionospheric very low frequency (VLF) transmitter, which is also broad band. Two approaches are studied that generate VLF waves in the ionosphere. The first, classic approach employs a ground-based HF heater to directly modulate the high latitude ionospheric, or auroral electrojet. In the classic approach, the intensity-modulated HF heater induces an alternating current in the electrojet, which serves as a virtual antenna to transmit VLF waves. The spatial and temporal variations of the electrojet impact the reliability of the classic approach. The second, beat-wave approach also employs a ground-based HF heater; however, in this approach, the heater operates in a continuous wave mode at two HF frequencies separated by the desired VLF frequency. Theories for both approaches are formulated, calculations performed with numerical model simulations, and the calculations are compared to experimental results. Theory for the classic approach shows that an HF heater wave, intensity-modulated at VLF, modulates the electron temperature dependent electrical conductivity of the ionospheric electrojet, which, in turn, induces an ac electrojet current. Thus, the electrojet becomes a virtual VLF antenna. The numerical results show that the radiation intensity of the modulated electrojet decreases with an increase in VLF radiation frequency. Theory for the beat wave approach shows that the VLF radiation intensity depends upon the HF heater intensity rather than the electrojet strength, and yet this approach can also modulate the electrojet when present. HF heater experiments were conducted for both the intensity modulated and beat wave approaches. VLF radiations were generated and the experimental results confirm the numerical simulations. Theory and experimental results both show that in the absence of the electrojet, VLF radiation from the F-region is generated via the beat wave approach. Additionally, the beat wave approach generates VLF radiations over a larger frequency band than by the modulated electrojet. V C 2015 AIP Publishing LLC.

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Experimental and Numerical Studies on ELF/VLF Wave Generation by Amplitude-Modulated HF Heating Waves

Cited by 16 publications

References 23 publications

Determination of the height of the modulated electrojet region generating ELF radiation

Determination of the height of the modulated electrojet region generating ELF radiation

VLF wave generation by amplitude‐modulated HF heater waves at Gakona, Alaska

Ionospheric very low frequency transmitter

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