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

Maxworth, Ashanthi; Gołkowski, Mark; Cohen, M. B.; Moore, R. C.; Chorsi, Hamid T.; Gedney, Stephen D.; Jacobs, Ryan T.

doi:10.1002/2015rs005683

Cited by 23 publications

(12 citation statements)

References 39 publications

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“…The local HAARP-generated ELF/VLF signals are expected to have eccentricity close to linear (ecc = 1) since the HAARP ELF/VLF generation process is known to be similar to that of an electric dipole antenna [Cohen et al, 2008;Maxworth et al, 2015]. This consistency with the theory and past work can be seen in Figures 4a and 4c with local HAARP pulses showing up in red (ecc ≈ 1).…”

Section: Analysis Of Eccentricity and Arrival Azimuthsupporting

confidence: 84%

“…Recording two components of the wave magnetic fields enables us to calculate the arrival azimuth angle and the eccentricity of the received emissions. In this context we follow the method used by and Maxworth et al [2015] where the EW and NS channels are combined as the imaginary and real part, respectively, of a complex signal. Applying the fast Fourier transform, the composite complex signal is put into the frequency domain as…”

Section: Observationsmentioning

confidence: 99%

“…Although in general magnetospheric whistler mode Journal of Geophysical Research: Space Physics 10.1002/2017JA024072 Journal of Geophysical Research: Space Physics 10.1002/2017JA024072 emissions can propagate obliquely and have elliptical polarizations, the requirement for waves reaching a ground-based receiver to have propagated in the ducted mode means that their polarization must be close to circular (ecc < <1) in the immediate vicinity of the ionospheric exit point. However, once RHCP waves propagate inside the Earth-ionosphere waveguide, they quickly convert to linear polarization upon reflection from the ground and ionosphere [Maxworth et al, 2015]. These reflections change the eccentricity of the polarization and make the waves be more linearly polarized (ecc ≈ 1).…”

Section: Observationsmentioning

confidence: 99%

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Unique concurrent observations of whistler mode hiss, chorus, and triggered emissions

2017

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We present a unique 2 h ground‐based observation of concurrent magnetospheric hiss, chorus, VLF triggered emissions as well as ELF/VLF signals generated locally by the High Frequency Active Auroral Research Program (HAARP) facility. Eccentricity of observed wave polarization is used as a criteria to identify magnetospheric emissions and estimate their ionospheric exit points. The observations of hiss and chorus in the unique background of coherent HAARP ELF/VLF waves and triggered emissions allow for more accurate characterization of hiss and chorus properties than in typical ground‐based observations. Eccentricity and azimuth results suggest a moving ionospheric exit point associated with a single ducted path at L ~ 5. The emissions exhibit dynamics in time suggesting an evolution of a magnetospheric source from hiss generation to chorus generation or a moving plasmapause location. We introduce a frequency band‐limited autocorrelation method to quantify the relative coherency of the emissions. A range of coherency was observed from high order of coherency in local HAARP transmissions and their echoes to lower coherency in natural chorus and hiss emissions.

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Section: Analysis Of Eccentricity and Arrival Azimuthsupporting

confidence: 84%

Section: Observationsmentioning

confidence: 99%

Section: Observationsmentioning

confidence: 99%

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Unique concurrent observations of whistler mode hiss, chorus, and triggered emissions

2017

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“…Using the ionospheric heaters of High Frequency Active Auroral Research Program (HAARP), several modulated heating experiments were carried out, and properties of ELF/VLF waves generated by electrojet modulation were presented, such as the azimuth, polarization, frequency dependence [4], and ELF/VLF perturbations by the DEMETER satellite [5]. Except rectangular wave modulation, the beat-wave heating technique [6] is one typical method to generate ELF/VLF waves.…”

Section: Introductionmentioning

confidence: 99%

Numerical Simulations of Elf/VLF Wave Generated by Modulated Beat-Wave Ionospheric Heating in High Latitude Regions

Li¹,

Zhan²,

Wu³

et al. 2016

PIER M

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Abstract-Based on the theory of ionospheric heating, with the self-consistent model in the low ionosphere, the Extremely-Low-Frequency (ELF) and Very-Low-Frequency (VLF) waves generated by modulated beat-wave ionospheric heating are analyzed theoretically. In the consideration of the stratified ionosphere, the magnetic fields generated by the equivalent ELF/VLF dipole source above the sea surface are studied by using the quasi-longitudinal approximation method. Taking the high latitude regions as an example, the variations of the electron temperature, the increments of Pedersen and Hall conductivities and the changing of the oscillating current density with the modulation frequency in beatwave heating are numerically discussed. The distribution of the magnetic fields is presented. It turns out that in high latitude regions, the efficiency of rectangular wave modulated heating in generating ELF/VLF wave is higher than that of modulated beat-wave heating, and the order of magnitude of the magnetic fields received above the sea surface is 10 −7 A/m in beat-wave modulation.

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“…The polarization ellipse technique has previously been applied to broadband signals to locate the arrival direction of chorus signals reentering the atmosphere from the space environment at high latitudes (Gołkowski & Inan, 2008;Poorya et al, 2017), as well as for direction finding of broadband sferics (Said et al, 2010). Maxworth et al (2015) also applied aspects of the polarization ellipse to coherent signals emitted by ionospheric ELF/VLF modulated HF heating. A portion of the magnetic flux density also exists in the vertical direction and is not always negligible (Silber et al, 2015).…”

Section: Polarization Definition and Utilitymentioning

confidence: 99%

Polarization of Narrowband VLF Transmitter Signals as an Ionospheric Diagnostic

et al. 2018

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Very low frequency (VLF, 3–30 kHz) transmitter remote sensing has long been used as a simple yet useful diagnostic for the D region ionosphere (60–90 km). All it requires is a VLF radio receiver that records the amplitude and/or phase of a beacon signal as a function of time. During both ambient and disturbed conditions, the received signal can be compared to predictions from a theoretical model to infer ionospheric waveguide properties like electron density. Amplitude and phase have in most cases been analyzed each as individual data streams, often only the amplitude is used. Scattered field formulation combines amplitude and phase effectively, but does not address how to combine two magnetic field components. We present polarization ellipse analysis of VLF transmitter signals using two horizontal components of the magnetic field. The shape of the polarization ellipse is unchanged as the source phase varies, which circumvents a significant problem where VLF transmitters have an unknown source phase. A synchronized two‐channel MSK demodulation algorithm is introduced to mitigate 90° ambiguity in the phase difference between the horizontal magnetic field components. Additionally, the synchronized demodulation improves phase measurements during low‐SNR conditions. Using the polarization ellipse formulation, we take a new look at diurnal VLF transmitter variations, ambient conditions, and ionospheric disturbances from solar flares, lightning‐ionospheric heating, and lightning‐induced electron precipitation, and find differing signatures in the polarization ellipse.

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

Cited by 23 publications

References 39 publications

Unique concurrent observations of whistler mode hiss, chorus, and triggered emissions

Unique concurrent observations of whistler mode hiss, chorus, and triggered emissions

Numerical Simulations of Elf/VLF Wave Generated by Modulated Beat-Wave Ionospheric Heating in High Latitude Regions

Polarization of Narrowband VLF Transmitter Signals as an Ionospheric Diagnostic

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