ELF waves generated by modulated HF heating of the auroral electrojet and observed at a ground distance of ∼4400 km

Moore, R. C.; Inan, U. S.; Bell, T. F.; Kennedy, Edward J.

doi:10.1029/2006ja012063

Cited by 54 publications

(51 citation statements)

References 22 publications

(50 reference statements)

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“…At the Arecibo Observatory in Puerto Rico and at the Jicamarca Observatory in Peru HF facilities were used to generate weak ELF signals with the equatorial electrojets [ Ferraro et al , ; Lunnen et al , ]. The European Incoherent Scatter facility located in Tromsø, Norway, the High Frequency Active Auroral Research Program (HAARP), and the Sura ionospheric heating facility in Russia have been extensively utilized for the modulation of auroral electrojets [ Stubbe et al , ; Barr and Stubbe , ; Moore et al , ; Fujimaru and Moore , ; Cohen et al , ; Gołkowski et al , ; Cohen and Golkowski , ; Kotik et al , ]. The two main modes of heating the ionosphere are called the ordinary mode ( O mode) and the extraordinary mode ( X mode).…”

Section: Introductionmentioning

confidence: 99%

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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Section: Introductionmentioning

confidence: 99%

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

et al. 2015

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“…More recently, the HAARP near‐field phased‐array HF facility near Gakona, Alaska (62° 22′ N, 145° 9′ W), has been used to generate ELF/VLF signals that have been observed as far as 4400 km [ Moore et al , 2007; Cohen et al , 2010c], as well as injected into the magnetosphere and observed in the geomagnetic conjugate region [ Inan et al , 2004; Gołkowski et al , 2008, 2011]. In 2007, an upgrade of HAARP was completed, increasing its capacity from 48 active elements, 960 kW input power, and 175 MW ERP (at 3.25 MHz), to 180 active elements, 3.6 MW input power, and ∼400 MW ERP (at 3.25 MHz).…”

Section: Introductionmentioning

confidence: 99%

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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“…A number of breakthroughs in ELF/VLF generation have taken place since it was completed in February 2007. Generated ELF/VLF signals detected at ∼700 km distance were found to be useful as a diagnostic of the auroral electrojet direction [ Cohen et al , ], with signals detected surprisingly strongly as far as 4400 km distance [ Cohen et al , ] following a weaker detection at that distance prior to the final power upgrade [ Moore et al , ]. HAARP ELF/VLF signals were observed to be injected into space [ Piddyachiy et al , ] and detected at the geomagnetic conjugate region [ Gołkowski et al , ], as well as a second echo near HAARP [ Gołkowski et al , ], with the received signals useful as a magnetospheric probing source [ Gołkowski et al , ].…”

Section: Introductionmentioning

confidence: 99%

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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ELF waves generated by modulated HF heating of the auroral electrojet and observed at a ground distance of ∼4400 km

Cited by 54 publications

References 22 publications

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

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

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

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

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