Modeling diurnal variations of the IAR parameters

Fedorov, E. N.; Mazur, N. G.; Пилипенко, В. А.; Ermakova, E. N.

doi:10.1007/s40328-015-0158-9

Cited by 14 publications

(16 citation statements)

References 48 publications

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“…The f 0 F 2 rise by a few MHz until after midnight before falling slowing again. At dawn, the f 0 F 2 rise again to over 8 MHz as sunlight begins to reionize the atmosphere (Fedorov, Mazur, Pilipenko, & Ermakov, ). The IAR fringe values, selected by hand by picking a single‐representative fringe from each of the six spectrograms, are shown as black points on an inverted scale in hertz (values on the right‐hand axis).…”

Section: Observations Of Sr and Iar At Eskdalemuirmentioning

confidence: 99%

Observation of Ionospheric Alfvén Resonances at 1–30 Hz and Their Superposition With the Schumann Resonances

Beggan

Musur

2018

JGR Space Physics

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Long-term measurements of the high-frequency magnetic field (0.1-100 Hz) have been made at Eskdalemuir Observatory in the United Kingdom since September 2012. We analyze five years of dynamic spectrograms to examine the occurrence and behavior of the Schumann and ionospheric Alfvén resonances (IAR) and Pc1 pulsations. The resonances, observed as diffuse bands, arise from reflections of energy both within the Earth-ionosphere cavity and from the nonlinear conductivity gradient of the ionosphere. Schumann Resonances (SR) occur continuously but IAR are observed to arise at local nighttime in ∼50% of days in the data set. Typically, IAR are found at frequencies of 1-8 Hz, but we find them extending out to 30 Hz and strongly superimposing over the first three Schumann resonances around 9% of the time. These phenomena include constructive and destructive interference, nonlinear frequency changes over the span of several hours, and polarity enhancements. In addition, the magnitude of the IAR does not decline rapidly with frequency as often proposed. We find that the IAR and their superposition with SR are strongly controlled by season and geomagnetic activity. We compare 6 days with the most unusual IAR behavior in the data set to ionosonde measurements of f 0 F 2 , a proxy for ionospheric conductivity but find little correlation. We suggest that, as current theoretical modeling does not account for these observations, further work is needed to understand how they arise. Plain Language Summary Measurements of the very rapid changes of the Earth's magnetic field(changes at a rate of between 1 and 50 times per second) show very weak repeating patterns. They are caused by magnetic fields from lightning strikes in thunderstorms near the equator. The lightning strikes are strong enough to "echo" around the globe repeatedly for a few seconds before fading, similar to the sound from a resonating bell. These patterns repeat at fixed periods of around 8, 14, and 21 times per second and are called the Schumann resonances. At night time, other patterns appear in the measurements caused by magnetic waves temporarily trapped in the upper atmosphere (called the ionosphere) between heights of 100 and 1,000 km. These patterns are labeled the ionospheric Alfvén resonances are a relatively unstudied feature of the Earth's magnetic field. We looked at these patterns in magnetic field data collected from Eskdalemuir Observatory in the United Kingdom over the past 5 years. We checked how often these types of patterns occurred and found a link to the seasons and how active, in general, the magnetic field is. We also found unusual and currently unexplained patterns including interference between the Schumann and ionospheric Alfvén resonances.

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Section: Observations Of Sr and Iar At Eskdalemuirmentioning

confidence: 99%

Observation of Ionospheric Alfvén Resonances at 1–30 Hz and Their Superposition With the Schumann Resonances

Beggan

Musur

2018

JGR Space Physics

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“…In an oblique coordinate system { x 1 , x 2 , x 3 } full‐wave equations for the tensor have been derived in Fedorov, Mazur, Pilipenko, and Ermakova (). The finite field‐aligned conductivity (

σ_{∥} \propto ϵ_{∥}

) due to electron collisions in the ionosphere produces a diffusion and absorption of electromagnetic wave structures with small transverse scales ≤2 km (Lessard & Knudsen, ).…”

Section: Model Of Alfvén Wave Beam Interaction With the Ionospherementioning

confidence: 99%

“…The finite field‐aligned conductivity (

σ_{∥} \propto ϵ_{∥}

) due to electron collisions in the ionosphere produces a diffusion and absorption of electromagnetic wave structures with small transverse scales ≤2 km (Lessard & Knudsen, ). For Alfvén waves with large horizontal scales, much larger than the skin depth δ ∥ determined by the field‐aligned conductivity σ ∥ , the general system from Fedorov, Mazur, Pilipenko, and Ermakova () reduces to the following set of equations:

\begin{matrix} \partial_{3} B_{1} & = i k_{1} \cot I B_{1} + (\frac{- i k_{1} k_{2}}{ω} + \frac{ω μ_{0} g}{\sin I}) E_{1} + (\frac{i k_{1}^{2}}{ω} - iω μ_{0} ϵ_{⊥}) E_{2} \\ \partial_{3} B_{2} & = i k_{2} \cot I B_{1} + (\frac{- i k_{2}^{2}}{ω} + \frac{iω μ_{0} ϵ_{⊥}}{\sin I^{2}}) E_{1} + (\frac{i k_{1} k_{2}}{ω} + \frac{ω μ_{0} g}{\sin I}) E_{2} \\ \partial_{3} E_{1} & = iω B_{2}, \partial_{3} E_{2} = - iω B_{1} - i k_{2} (\cot I) E \end{matrix}

…”

Section: Model Of Alfvén Wave Beam Interaction With the Ionospherementioning

confidence: 99%

“…The significance of the mode coupling between Alfvén wave and IFW modes in a realistic ionosphere received a special consideration in Fedorov, Mazur, Pilipenko, and Ermakova ().…”

Section: Model Of Alfvén Wave Beam Interaction With the Ionospherementioning

confidence: 99%

“…Fedorov, Mazur, Pilipenko, and Ermakova () developed a numerical model of the magnetospheric Alfvén wave interaction with the ionosphere based on the solution of multifluid MHD full‐wave equations in a realistic ionosphere, whose parameters were reconstructed from the IRI model. In Fedorov, Mazur, Pilipenko, and Engebretson () the transmission/reflection coefficients have been calculated for a wave spatial harmonic, characterized by the horizontal wave vector k ⊥ .…”

Section: Introduction: Pc1 Waves and Transmission/reflective Propertimentioning

confidence: 99%

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Transmission of a Magnetospheric Pc1 Wave Beam Through the Ionosphere to the Ground

et al. 2018

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A characteristic feature of the upper ionosphere is the occurrence of the ionospheric Alfvén resonator (IAR) and the ionospheric fast-mode waveguide (IFW), which can trap electromagnetic wave energy in the Pc1 frequency range from fractions of a hertz to a few hertz. This wave trapping ensures the dependence of ionospheric transmission/reflective properties on frequency. We numerically model magnetospheric Alfvén wave transmission through the ionosphere to the ground based on solution of the magnetohydrodynamic full-wave equations in a realistic ionosphere, whose parameters are reconstructed from the International Reference Ionosphere model. The spatial structure of an incident wave is modeled as a localized beam with a finite latitudinal scale ⟂ and an azimuthally propagating wave. The IAR and IFW modes are coupled owing to the Hall conductivity and geomagnetic field inclination. Ground spatial and spectral structures of the Pc1 wave (0.1-to 6-Hz band) have been calculated for summer day/night conditions at the Antarctic Halley observatory, though results may be qualitatively applied to any midlatitude site. An incident wave with azimuthal wave vector k y = 1.7 ⋅ 10 −3 km −1 , and ⟂ = 10 2 km has been considered. The model predicts that beneath the incident beam the ground magnetic response "duplicates" its structure after accounting for a ∕2 rotation and some latitudinal shift/widening. The transmission has an oscillatory dependence on frequency, thus forming "transmission windows" at resonant frequencies of IAR and IFW modes. The spectra vary depending on distance from an incidence point. Interference between IFW modes is revealed in the nonmonotonic and frequency-dependent character of latitudinal variations of wave amplitude.

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Interaction of magnetospheric Alfvén waves with the ionosphere in the Pc1 frequency band

et al. 2016

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A characteristic feature of the upper ionosphere is the occurrence of the ionospheric Alfvén resonator (IAR) and MHD waveguide, which can trap electromagnetic wave energy in the range from fractions of a Hz to a few Hz. This wave trapping ensures the strong dependence of the ionospheric transmission/reflective properties on frequency. We have developed a numerical model of the magnetospheric Alfvén wave interaction with the ionosphere and transmission to the ground based on the solution of multifluid magnetohydrodynamic (MHD) full wave equations in a realistic ionosphere, whose parameters were reconstructed from the International Reference Ionosphere model. The MHD modes are coupled owing to the frequency‐dependent Hall conductivity and geomagnetic field line inclination. This model can be applied to the interpretation of the spectral structure of electromagnetic emissions of the magnetospheric origin in the band 0.1–10 Hz observed at various latitudes. The model predicts that the upper part of the ULF spectrum (f > 1 Hz) will be severely absorbed upon wave transmission through the daytime ionosphere to the ground. At nighttime the transmission coefficient of Alfvén waves has an oscillatory dependence on frequency, with “transmission windows” at the lowest IAR eigenfrequencies (<3 Hz). At higher frequencies (3–10 Hz) the reflection/transmission coefficients are dominated by periodic scale‐dependent modulation owing to the waveguide modes. Broad maxima/minima of the transmission coefficient are determined by the phasing between Alfvén and fast magnetosonic waves at the bottom of the ionosphere.

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Modeling diurnal variations of the IAR parameters

Cited by 14 publications

References 48 publications

Observation of Ionospheric Alfvén Resonances at 1–30 Hz and Their Superposition With the Schumann Resonances

Observation of Ionospheric Alfvén Resonances at 1–30 Hz and Their Superposition With the Schumann Resonances

Transmission of a Magnetospheric Pc1 Wave Beam Through the Ionosphere to the Ground

Interaction of magnetospheric Alfvén waves with the ionosphere in the Pc1 frequency band

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