Studying the Variations of the Broadband Spectral Maximum Parameters in the Natural ULF Fields

Ermakova, E. N.; Kotik, D. S.; Ryabov, A.V.; Pershin, A. V.; Bösinger, T.; Zhou, K

doi:10.1007/s11141-013-9398-0

Cited by 8 publications

(14 citation statements)

References 8 publications

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“…We note that Ermakova et al () attempted to model low‐frequency (1–8 Hz) IAR features observed in Crete by Bösinger et al (, ) based on a layered ionospheric model but also failed to fully describe the measurements. The modeling by Schekotov et al () may be able account for the high‐frequency fringes observed above 8 Hz, though this relies on the occurrence regional lightning storms to enhance the IAR.…”

Section: Discussionmentioning

confidence: 92%

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: Discussionmentioning

confidence: 92%

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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“…It is shown in [3,4] that it is exactly the presence of a resonant sub-IAR cavity that generates a more abrupt increase in the longitudinal component of the ULF field, as well as the frequency dependence of the phase shift betweeen the horizontal magnetic components. This changes significantly the frequency dependence of the azimuthal angle of the principal axis of the background noise polarization ellipse.…”

Section: Studying the Sub-iar Structure Effect On The Spatial Orientamentioning

confidence: 99%

“…When the excitation of the sub-IAR structure by regional thunderstorm sources is studied, the main attention is paid to frequency dependences of the degree of circular polarization of magnetic noise since this parameter describes most adequately the effect of this ionospheric structure on spectral features of the ULF fields. In [4], it was shown on the basis of theoretical calculations that the main characteristics of the frequency dependence of the parameter ε are independent of the source direction and are determined by the parameters of the local ionosphere. The presence of a sub-IAR leads to characteristic variations in the frequency dependence of the parameter ε.…”

Section: Introductionmentioning

confidence: 99%

Studying the Effect of the Local Thunderstorm Cells on the Background ULF Magnetic Noise Parameter Spectra

Ermakova

Kotik

Ryabov

et al. 2015

Radiophys Quantum El

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We study the effect of the masking factor from the local thunderstorm cells on ULF magnetic field spectra with the inhomogeneous electron-density structures existing in the local ionosphere (ionospheric and lower ionospheric Alfvén resonators). Using an original data-processing technique for recording of horizontal magnetic components at the midlatitude reception point Novaya Zhizn', we have examined the contribution of the sources located at different distances from the reception point to the formation of the background noise spectra. The ULF signal processing technique permitted us to reduce the pulse component of magnetic noise in amplitude above a certain threshold and thus rule out the effect of a local thunderstorm activity. Frequency dependences of the azimuthal angle of the principal axis of the magnetic noise polarization ellipse are also analyzed. It is shown that the presence of the lower ionospheric Alfvén resonator leads to a nonmonotonic dependence of the azimuthal angle on the frequency. It was found that the local thunderstorms within 60-80 km from the reception point completely mask the manifestation of the lower ionospheric Alfvén resonator in the ULF noise polarization parameters. To spot the local thunderstorm cells, we used the data from the meteorological radar facility MRL-4 in Nizhny Novgorod.

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“…It was facilitated by the fact that another phenomenon was discovered [ Belyaev , ] and explored to a significant extent [ Ermakova et al, , ]. It was called broadband spectral maximum (BSM).…”

Section: Introductionmentioning

confidence: 99%

“…Just like the pulsating ellipticity ε discussed here, it is a nighttime property of MBN and occurs in the same frequency range as the pulsating ε , i.e., usually at frequencies above SRS but below the Schumann resonance. BSM may or may not occur in conjunction with the pulsating ε , but an intimate relationship between both phenomena could be established [ Ermakova et al , ]: if BSM does occur, then the frequency of the maximum spectral power coincides with the frequency at which ε changes sign ( ε is defined between plus and minus unity). Based on this finding it was not difficult to guess that both phenomena may have a common origin.…”

Section: Introductionmentioning

confidence: 99%

Pulsating nighttime magnetic background noise in the upper ULF band at low latitudes

et al. 2014

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We model long-period (~2 h) irregular pulsations in the ellipticity of magnetic background noise (MBN) in the upper ULF band which were frequently observed during nighttime at a low-latitude site on the Island of Crete. It is shown that such pulsations cannot be reproduced in the calculations when using the ionosphere parameters from the statistical IRI (International Reference Ionosphere) model, while regular diurnal signatures of the ellipticity spectrum at sunset and sunrise are successfully reproduced. We apply the same approach to the location of the Arecibo incoherent scatter radar and show that using actually measured ionosphere profiles (up to a height of 400 km) instead of IRI profiles produces the ellipticity pulsations very similar to those observed at Crete. Comparison of model results with the calculated behavior of Alfvén mode refractive index allows us to conclude that the observed nighttime long-period irregular pulsations in the MBN ellipticity are caused by dynamic processes at the upper boundary of the ionospheric E-F valley which serves as a subionospheric Alfvén resonator. Irregular widening, shrinking, and/or deepening of the valley with time scales of 1 to 4 h affect the electrodynamical properties of this resonator and manifest themselves in the magnetic background noise properties.

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Studying the Variations of the Broadband Spectral Maximum Parameters in the Natural ULF Fields

Cited by 8 publications

References 8 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

Studying the Effect of the Local Thunderstorm Cells on the Background ULF Magnetic Noise Parameter Spectra

Pulsating nighttime magnetic background noise in the upper ULF band at low latitudes

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