Orientation of the HAARP ELF ionospheric dipole and the auroral electrojet

Cohen, M. B.; Gołkowski, Mark; Inan, U. S.

doi:10.1029/2007gl032424

Cited by 35 publications

(40 citation statements)

References 18 publications

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“…Similar effects could occur if the electrojet changes direction which may not be captured by changes in only the magnetometer H component. We did not observe changes in the prevalence of negative and uncorrelated cases when using the total horizontal current (including both the H and D components), but the direction of the electrojet can still change ELF amplitude through changes in waveguide excitation even if the total horizontal current remains unchanged [ Cohen et al , 2008].…”

Section: Discussionmentioning

confidence: 99%

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Relationship between electrojet current strength and ELF signal intensity in modulated heating experiments

2009

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[1] The High Frequency Active Auroral Research Program (HAARP) facility is used to generate waves in the extremely low frequency (ELF) range via modulated HF heating of the ionosphere. This HF heating modulates the electron temperature in the D region ionosphere and leads to modulated conductivity and a time-varying current which then radiates at the modulation frequency. We investigate the relationship between the intensity of the HAARP-generated ELF signal and the strength of the east-west component of the auroral electrojet as measured by a ground-based magnetometer. We find that under all magnetic conditions, HAARP can generate ELF radiation detectable 37 km away with 73% of tones having an amplitude exceeding 0.15 pT. While strong ELF amplitudes (>1.5 pT) were most common during an enhanced electrojet, a weak electrojet can also support equally high ELF amplitudes. The relative change in ELF amplitude per unit change in electrojet current strength is inversely proportional to the absolute current strength. We interpret the dynamic relationship between ELF amplitude and electrojet current strength in terms of the time-variable ionospheric parameters and HF heating efficiency.Citation: Jin, G., M. Spasojevic, and U. S. Inan (2009), Relationship between electrojet current strength and ELF signal intensity in modulated heating experiments,

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Section: Discussionmentioning

confidence: 99%

“…The HAARP ionospheric heater has been used in various ELF/VLF wave generation experiments since 1999 [e.g., Milikh et al , 1999; Rodriguez et al , 1999; Cohen et al , 2008]. All data presented here were collected after its final upgrade in 2007.…”

Section: Methodsmentioning

confidence: 99%

Relationship between electrojet current strength and ELF signal intensity in modulated heating experiments

2009

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“…This paper presents results from a detailed, numerical study of the propagation of whistler mode waves transmitted by the High Frequency Active Aurora Research Program (HAARP) facility in Gakona, Alaska. The HAARP facility is an ionospheric heater that is able to generate extremely low frequency (ELF)/very low frequency (VLF) waves by modulating the ionospheric conductivity in the D region and thus modify the auroral electrojet currents [ Papadopoulos et al , 2003; Gołkowski et al , 2008; Cohen et al , 2008]. In the absence of conventional transmitters in the ELF/VLF: 500 Hz to 8 kHz band (Siple Station was discontinued in 1988), HAARP provides a unique platform for controlled wave injection studies.…”

Section: Introductionmentioning

confidence: 99%

Propagation of whistler mode waves with a modulated frequency in the magnetosphere

et al. 2010

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[1] This paper presents results from experimental and numerical studies of the propagation of whistler mode waves in the Earth's magnetosphere. An experiment conducted at the High Frequency Active Auroral Research Program (HAARP) on 16 March 2008 demonstrates that ionospherically generated waves with particular frequency-time formats are amplified on their pass from HAARP to the conjugate location in the South Pacific Ocean more efficiently than waves with a constant frequency. Numerical simulations of a one-dimensional electron magnetohydrodynamics (MHD) model in the dipole magnetic field geometry reveal that the amplification takes place more efficiently when the frequency of the whistler mode waves (in the frequency range from 0.5 to 1.0 kHz) changes in the equatorial magnetosphere with the rate from 0.25 to 0.47 kHz/s. The maximum amplification occurs when this rate is 0.33 kHz/s and no/very little amplification is observed when this gradient is equal to 0 or when it is larger than 0.78 kHz/s.

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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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Orientation of the HAARP ELF ionospheric dipole and the auroral electrojet

Cited by 35 publications

References 18 publications

Relationship between electrojet current strength and ELF signal intensity in modulated heating experiments

Relationship between electrojet current strength and ELF signal intensity in modulated heating experiments

Propagation of whistler mode waves with a modulated frequency in the magnetosphere

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

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