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

Kuo, Spencer; Wu, Yen Liang; Pradipta, Rezy; Cohen, Joel A.; Lee, M. C.

doi:10.1029/2008gl034414

Cited by 9 publications

(9 citation statements)

References 27 publications

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“…Results of three experiments, 12 The N-S and E-W components of the radiation magnetic field from the first two experiments and the radiation spectral power density from the third experiment are presented in the first row of Fig. 2.…”

Section: A Generation Of Vlf Radiation By Electrojet Modulationmentioning

confidence: 98%

“…The fractional energy loss term on the LHS of Eq. (12) involves both elastic and inelastic collisions. The main processes involved in the inelastic collisions in the energy range of interest (<6 eV) are the rotational and vibration excitation of N 2 and O 2 .…”

Section: Which Is Set Up Via a Beat Wave Approachmentioning

confidence: 99%

“…In the presence of HF heating, the electron temperature is governed by the electron thermal energy equation 25,26 @T e =@t þ ð2T e =3Þ$ Á v e þ dðT e Þ e ðT e ÞðT e À T n Þ þ ionization loss ¼ ð2=3n 0 ÞðQ þ $ Á K e Á $T e Þ þsolar heat input; (12) where v e is the electron fluid velocity, d(T e ) is the average relative energy fraction lost in each collision, e (T e ) is the effective collision frequency of electrons with neutral particles (it accounts for both elastic and inelastic collisions), T n is the temperature of the background neutral particles; the ionization loss becomes significant as electrons are heated up to high temperature; Q is the total Ohmic heating power density in the background plasma and contributed by the electrojet current and the HF heater wave, K e ¼ (xx þŷŷ) K ? þẑẑ K z is the thermal conduction tensor, K z ¼ 3n 0 T e /m e , K ?…”

Section: A Formulation Of Electrojet Modulationmentioning

confidence: 99%

“…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%

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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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Section: A Generation Of Vlf Radiation By Electrojet Modulationmentioning

confidence: 98%

Section: Which Is Set Up Via a Beat Wave Approachmentioning

confidence: 99%

Section: A Formulation Of Electrojet Modulationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Ionospheric very low frequency transmitter

Kuo

2015

Physics of Plasmas

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“…These density irregularities could also couple to the temporally modulated electrojet (background current) to produce a whistler mode current and the associated whistler (VLF) wave at the beat frequency [Kuo et al, 1999b;Kuo and Koretzky, 2001]. A similar process for VLF wave generation by an intensity modulated HF heater was analyzed and revealed experimentally by Kuo et al [2008]. In the second cycle of the experiments, the experiment time was enough only for repeating four beat frequencies at 1, 2, 3.5, and 5.5 kHz, i.e., the experiment was stopped after generating 5.5 kHz signal.…”

Section: Generation Of Vlf Wavesmentioning

confidence: 99%

Observation and theory of whistler wave generation by high‐power HF waves

et al. 2013

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[1] Summer midnight and afternoon VLF wave generation comparison experiments were conducted on 25 July and 27 July 2011, respectively, using two CW HF X-mode waves with 11 VLF frequency differences from 2 to 21.5 kHz. The background magnetic variations were at comparable levels. During the afternoon experiment, the D region absorption was significant and increasing. The number of the ionogram echoes decreased during the afternoon experiment. VLF signals were detected from 2 to 7.6 kHz in both experiments, showing an inverse frequency dependence of intensity, although signal intensity (except at 5.5 kHz) detected during the midnight experiment was stronger than the corresponding afternoon intensity before observing a decrease of the number of ionogram echoes. However, VLF signals from 11.5 to 21.5 (except at 19.6 kHz) were also generated in the afternoon experiment concurrent with a decrease of the O-mode ionosonde echoes from 2 to 4 MHz. The concurrence of a decrease of the afternoon ionogram echoes, the unexpected generation of VLF waves at higher frequencies, and the increasing D region absorption throughout the experiment may be explained by the generation of large-scale density irregularities, which scatter the ionosonde signals as well as couple with the modulated electrojet to generate whistler waves. A theoretical formulation of the coupling mechanism for the whistler wave generation is presented.

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HF beam parameters in ELF/VLF wave generation via modulated heating of the ionosphere

Cohen¹,

Gołkowski²,

Lehtinen³

et al. 2012

J. Geophys. Res.

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[1] ELF/VLF (0.3-30 kHz) wave generation is achievable via modulated HF (3-30 MHz) heating of the lower ionosphere in the presence of natural currents such as the auroral electrojet. Using the 3.6 MW High Frequency Active Auroral Research Program (HAARP) facility near Gakona, AK, we investigate the effect of HF frequency and beam size on the generated ELF/VLF amplitudes, as a function of modulation frequency, and find that generation in the Earth-ionosphere waveguide generally decreases with increasing HF frequency between 2.75-9.50 MHz. HAARP is also capable of spreading the HF power over a wider area, and we find that a larger beam area yields larger generated amplitudes on the ground. Measurements are shown to generally agree with a theoretical model, which is then applied to also predict the effect of HF beam parameters on magnetospheric injection with HAARP.

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

Cited by 9 publications

References 27 publications

Ionospheric very low frequency transmitter

Ionospheric very low frequency transmitter

Observation and theory of whistler wave generation by high‐power HF waves

HF beam parameters in ELF/VLF wave generation via modulated heating of the ionosphere

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