Dual‐beam ELF wave generation as a function of power, frequency, modulation waveform, and receiver location

Agrawal, D. C.; Moore, R. C.

doi:10.1029/2012ja018061

Cited by 7 publications

(11 citation statements)

References 28 publications

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“…with υ ei being the electron-ion collisional frequency at the reflection point; it is derived from Banks and Kocharts (1973) and Schunk and Nagy (1978), while the exact expression of υ e2 in S anom can be found in . The peak electric field amplitude E 0 is estimated by an empirical formula:…”

Section: Hf Heating Modelmentioning

confidence: 99%

“…with ω ce = eB 0 m e and ω ci = eB 0 m i being the ion and electron cyclotron frequencies, θ the dip angle of the ambient geomagnetic field, and υ en and υ in the electron-neutral and ion-neutral collisional rates, respectively, both of which can be calculated according to Banks and Kocharts (1973) and Schunk and Nagy (1978) as in the HF heating model.…”

Section: Model Of Ulf Wave Generation and Propagationmentioning

confidence: 99%

“…K e is the parallel coefficient of thermal conductivity which takes the form of (Banks and Kocharts, 1973) K e = 7.75 × 10 5 T 2.5 e 1 + 3.22 × 10 4 T 2 e /n e n N n Q n eV cm…”

Section: Hf Heating Modelmentioning

confidence: 99%

“…υ en and υ in are electron-neutral and ion-neutral collisional rates, respectively, both of which are calculated from Banks and Kocharts (1973) and Schunk and Nagy (1978).…”

Section: Hf Heating Modelmentioning

confidence: 99%

“…This hypothesis was first suggested by Willis and Davis (1973) and was then proved when artificially excited low-frequency signals were detected in an experiment for the first time (Getmantsev et al, 1974). A series of experiments of generating low-frequency waves following this mechanism were carried out at the European Incoherent Scatter Scientific Association (EISCAT) and the High Frequency Active Auroral Research Program (HAARP; Cohen et al, 2012;Agrawal and Moore, 2012;Ferraro et al, 1984;Papadopoulos et al, 2003), and this mechanism was named PEJ (polar electrojet) (Stubbe and Kopka, 1977;Barr et al, 1991). The method of artificially generating low-frequency waves by modulating the lower ionosphere is completely dependent on the existence of quasi-stationary ionospheric currents, which to some extent limits the location of the heating facility to the high and equatorial latitudes and also makes the generation of ULF waves more unpredictable (Papadopoulos et al, 2011b).…”

Section: Introductionmentioning

confidence: 99%

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Numerical study of the generation and propagation of ultralow-frequency waves by artificial ionospheric F region modulation at different latitudes

Xu¹,

Zhou²,

Shi³

et al. 2016

Ann. Geophys.

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Abstract. Powerful high-frequency (HF) radio waves can be used to efficiently modify the upper-ionospheric plasmas of the F region. The pressure gradient induced by modulated electron heating at ultralow-frequency (ULF) drives a local oscillating diamagnetic ring current source perpendicular to the ambient magnetic field, which can act as an antenna radiating ULF waves. In this paper, utilizing the HF heating model and the model of ULF wave generation and propagation, we investigate the effects of both the background ionospheric profiles at different latitudes in the daytime and nighttime ionosphere and the modulation frequency on the process of the HF modulated heating and the subsequent generation and propagation of artificial ULF waves. Firstly, based on a relation among the radiation efficiency of the ring current source, the size of the spatial distribution of the modulated electron temperature and the wavelength of ULF waves, we discuss the possibility of the effects of the background ionospheric parameters and the modulation frequency. Then the numerical simulations with both models are performed to demonstrate the prediction. Six different background parameters are used in the simulation, and they are from the International Reference Ionosphere (IRI-2012) Jicamarca (11.95 • S, 76.87 • W) at 02:00 and 14:00 LT. A modulation frequency sweep is also used in the simulation. Finally, by analyzing the numerical results, we come to the following conclusions: in the nighttime ionosphere, the size of the spatial distribution of the modulated electron temperature and the ground magnitude of the magnetic field of ULF wave are larger, while the propagation loss due to Joule heating is smaller compared to the daytime ionosphere; the amplitude of the electron temperature oscillation decreases with latitude in the daytime ionosphere, while it increases with latitude in the nighttime ionosphere; both the electron temperature oscillation amplitude and the ground ULF wave magnitude decreases as the modulation frequency increases; when the electron temperature oscillation is fixed as input, the radiation efficiency of the ring current source is higher in the nighttime ionosphere than in the daytime ionosphere.

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Section: Hf Heating Modelmentioning

confidence: 99%

Section: Model Of Ulf Wave Generation and Propagationmentioning

confidence: 99%

“…K e is the parallel coefficient of thermal conductivity which takes the form of (Banks and Kocharts, 1973) K e = 7.75 × 10 5 T 2.5 e 1 + 3.22 × 10 4 T 2 e /n e n N n Q n eV cm…”

Section: Hf Heating Modelmentioning

confidence: 99%

“…υ en and υ in are electron-neutral and ion-neutral collisional rates, respectively, both of which are calculated from Banks and Kocharts (1973) and Schunk and Nagy (1978).…”

Section: Hf Heating Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Numerical study of the generation and propagation of ultralow-frequency waves by artificial ionospheric F region modulation at different latitudes

Xu¹,

Zhou²,

Shi³

et al. 2016

Ann. Geophys.

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Multistation observations of the azimuth, polarization, and frequency dependence of ELF/VLF waves generated by electrojet modulation

et al. 2015

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Modulated ionospheric heating experiments are performed with the High Frequency ActiveAuroral Research Program facility in Gakona, Alaska, for the purpose of generating extremely low frequency (ELF) and very low frequency (VLF) waves. Observations are made at three different azimuths from the heating facility and at distances from 37 km to 99 km. The polarization of the observed waves is analyzed in addition to amplitude as a function of modulation frequency and azimuth. Amplitude and eccentricity are observed to vary with both azimuth and distance from the heating facility. It is found that waves radiated at azimuths northwest of the facility are generated by a combination of modulated Hall and Pedersen currents, while waves observed at other azimuths are dominated by modulated Hall currents. We find no evidence for vertical currents contributing to ground observations of ELF/VLF waves. Observed amplitude peaks near multiples of 2 kHz are shown to result from vertical resonances in the Earth-ionosphere waveguide, and variations of the frequency of these resonances can be used to determine the D region ionosphere electron density profile in the vicinity of the HF heater.

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100 days of ELF/VLF generation via HF heating with HAARP

Cohen

Gołkowski

2013

JGR Space Physics

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Extremely low frequency/very low frequency (ELF/VLF) radio waves are difficult to generate with conventional antennas. Ionospheric high frequency (HF) heating facilities generate ELF/VLF waves via modulated heating of the lower ionosphere. HF heating of the ionosphere changes the lower ionospheric conductivity, which in the presence of natural currents such as the auroral electrojet creates an antenna in the sky when heating is modulated at ELF/VLF frequencies. We present a summary of nearly 100 days of ELF/VLF wave generation experiments at the 3.6 MW High Frequency Active Auroral Research Program (HAARP) facility near Gakona, Alaska, at a variety of ELF/VLF frequencies, seasons, and times of day. We present comprehensive statistics of generated ELF/VLF magnetic fields observed at a nearby site, in the 500–3500 Hz band. Transmissions with a specific HF beam configuration (3.25 MHz, vertical beam, amplitude modulation) are isolated so the data comparison is self‐consistent, across nearly 5 million individual measurements of either a tone or a piece of a frequency‐time ramp. There is a minimum in the average generation close to local midnight. It is found that generation during local nighttime is on average weaker but more highly variable, with a small number of very strong generation periods. Signal amplitudes from day to day may vary by as much as 20–30 dB. Generation strengthens by ∼5 dB during the first ∼30 min of transmission, which may be a signature of slow electron density changes from sustained HF heating. Theoretical calculations are made to relate the amplitude observed to the power injected into the waveguide and reaching 250 km. The median power generated by HAARP and injected into the waveguide is ∼0.05–0.1 W in this baseline configuration (vertical beam, 3.25 MHz, amplitude modulation) but may have generated hundreds of watts for brief durations. Several efficiency improvements have improved the ELF/VLF wave generation efficiency further.

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Dual‐beam ELF wave generation as a function of power, frequency, modulation waveform, and receiver location

Cited by 7 publications

References 28 publications

Numerical study of the generation and propagation of ultralow-frequency waves by artificial ionospheric F region modulation at different latitudes

Numerical study of the generation and propagation of ultralow-frequency waves by artificial ionospheric F region modulation at different latitudes

Multistation observations of the azimuth, polarization, and frequency dependence of ELF/VLF waves generated by electrojet modulation

100 days of ELF/VLF generation via HF heating with HAARP

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