Confirmation of existence of the small-scale field-aligned currents in middle and low latitudes and an estimate of time scale of their temporal variation

Iwamoto, Toshihiko; Nakanishi, Koji; Aoyama, Tadashi; Yokoyama, Yoshihiko; Koyama, Yukinobu; Lühr, H.

doi:10.1002/2014gl062555

Cited by 22 publications

(31 citation statements)

References 10 publications

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“…As mentioned in "Introduction" section, Iyemori et al (2015) confirmed that the MRs having period around 10-30 s observed almost all the time along the satellite orbit by Swarm satellites are the spatial structures of small-scale FACs, and they also suggested that the typical timescale of the magnetic fluctuations is about 200, 296 and 340 s for the meridional component and 340 s for the zonal component. Nakanishi et al (2014) suggested that the small-scale FACs observed by CHAMP are caused by the ionospheric E-layer dynamo having the lower atmospheric origin.…”

Section: Discussionsupporting

confidence: 65%

“…Iyemori et al (2015) confirmed that the MRs observed by Swarm satellites on the initial orbits are spatial structure of FACs. Timescale of their temporal variations is roughly estimated to Open Access *Correspondence: aoyama@kugi.kyoto-u.ac.jp 1 Graduate School of Science, Kyoto University, Kyoto, Japan Full list of author information is available at the end of the article be 200-340 s, and amplitudes of the MRs shown in their paper are about 1 nT.…”

Section: Introductionsupporting

confidence: 71%

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Localized field-aligned currents and 4-min TEC and ground magnetic oscillations during the 2015 eruption of Chile’s Calbuco volcano

et al. 2016

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The Calbuco volcano in southern Chile erupted on April 22, 2015. About 2 h after the first eruption, a Swarm satellite passed above the volcano and observed enhancement of small-amplitude (~0.5 nT) magnetic fluctuations with wave-packet structure which extends 15° in latitude. Similar wave packet is seen at the geomagnetic conjugate point of the volcano. Just after the eruption, geomagnetic fluctuations with the spectral peaks around the vertical acoustic resonance periods, 215 and 260 s, were also observed at Huancayo Geomagnetic Observatory located on the magnetic equator. Besides these observations, around 4-min, i.e., 175, 205 and 260 s, oscillations of total electron content (TEC) were observed at global positioning system stations near the volcano. The horizontal propagation velocity and the spatial scale of the TEC oscillation are estimated to be 720 m/s and 1600 km, respectively. These observations strongly suggest that the atmospheric waves induced by explosive volcanic eruption generate TEC variation and electric currents. The Swarm observation may be explained as a manifestation of their magnetic effects observed in the topside ionosphere.

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Section: Discussionsupporting

confidence: 65%

Section: Introductionsupporting

confidence: 71%

Localized field-aligned currents and 4-min TEC and ground magnetic oscillations during the 2015 eruption of Chile’s Calbuco volcano

et al. 2016

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“…Additionally, Swarm data are used to study the Sun's influence on the Earth system by analyzing electric currents in the magnetosphere and ionosphere and understanding the impact of solar wind on the dynamics of the upper atmosphere. Swarm currently offers one of the best-ever surveys of the Earth's main and crustal magnetic field (Civet et al, 2015;De Michelis et al, 2015;Hulot et al, 2015;Olsen et al, 2015;Schnepf et al, 2015) as well as the near-Earth electromagnetic environment (Alken et al, 2015;Archer et al, 2015;Buchert et al, 2015;Dunlop et al, 2015;Goodwin et al, 2015;Iyemori et al, 2015;Lühr et al, 2015a, b;Park et al, 2015;Pitout et al, 2015;Spicher et al, 2015). The interested reader is also referred to the special issue "Swarm science results after 2 years in space" (for details, see Olsen et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

An initial ULF wave index derived from 2 years of Swarm observations

et al. 2018

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Abstract. The ongoing Swarm satellite mission provides an opportunity for better knowledge of the near-Earth electromagnetic environment. Herein, we use a new methodological approach for the detection and classification of ultra lowfrequency (ULF) wave events observed by Swarm based on an existing time-frequency analysis (TFA) tool and utilizing a state-of-the-art high-resolution magnetic field model and Swarm Level 2 products (i.e., field-aligned currents -FACs -and the Ionospheric Bubble Index -IBI). We present maps of the dependence of ULF wave power with magnetic latitude and magnetic local time (MLT) as well as geographic latitude and longitude from the three satellites at their different locations in low-Earth orbit (LEO) for a period spanning 2 years after the constellation's final configuration. We show that the inclusion of the Swarm single-spacecraft FAC product in our analysis eliminates all the wave activity at high altitudes, which is physically unrealistic. Moreover, we derive a Swarm orbit-by-orbit Pc3 wave (20-100 MHz) index for the topside ionosphere and compare its values with the corresponding variations of solar wind variables and geomagnetic activity indices. This is the first attempt, to our knowledge, to derive a ULF wave index from LEO satellite data. The technique can be potentially used to define a new Level 2 product from the mission, the Swarm ULF wave index, which would be suitable for space weather applications.

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“…The perturbations of the total electron content are predicted to be detectable by groundbased radar and GPS receivers. Acoustic waves also drive field-aligned currents that may be detectable by in situ magnetometers (Iyemori et al, 2015). A recent paper (Zettergren and Snively, 2015) reports that the recent measurements of GPS-derived TEC reveals acoustic wave periods from ∼ 1 to 4 min in the F-region ionosphere following natural hazard events, such as earthquakes, severe weather fronts, and volcanoes.…”

mentioning

confidence: 99%

“…Moreover, in order to search the seismogenic effects in the ionosphere, it is necessary to unify the well-developed model of the electromagnetic channel to seismo-ionospheric coupling (Molchanov et al, 1995;Rapoport et al, 2004b;Grimalsky et al, 1999;Pulinets and Boyarchuk, 2004;Sorokin and Hayakawa, 2013) with the model of the acoustic channel (Gokhberg and Shalimov, 2000;Rapoport et al, 2004aRapoport et al, , 2009Koshevaya et al, 2002;Grimalsky et al, 2003;Zettergren and Snively, 2015;Iyemori et al, 2015). Traditionally, AGWs and electromagnetic waves have been considered as the basis of two main competitive mechanisms of seismo-ionospheric coupling (Sorokin and Hayakawa, 2013;Klimenko et al, 2011;Pulinets and Boyarchuk, 2004).…”

mentioning

confidence: 99%

Ground-based acoustic parametric generator impact on the atmosphere and ionosphere in an active experiment

Rapoport¹,

Cheremnykh²,

Koshovy³

et al. 2017

Ann. Geophys.

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Abstract. We develop theoretical basics of active experiments with two beams of acoustic waves, radiated by a ground-based sound generator. These beams are transformed into atmospheric acoustic gravity waves (AGWs), which have parameters that enable them to penetrate to the altitudes of the ionospheric E and F regions where they influence the electron concentration of the ionosphere. Acoustic waves are generated by the ground-based parametric sound generator (PSG) at the two close frequencies. The main idea of the experiment is to design the output parameters of the PSG to build a cascade scheme of nonlinear wave frequency downshift transformations to provide the necessary conditions for their vertical propagation and to enable penetration to ionospheric altitudes. The PSG generates sound waves (SWs) with frequencies f 1 = 600 and f 2 = 625 Hz and large amplitudes (100-420 m s −1 ). Each of these waves is modulated with the frequency of 0.016 Hz. The novelty of the proposed analytical-numerical model is due to simultaneous accounting for nonlinearity, diffraction, losses, and dispersion and inclusion of the two-stage transformation (1) of the initial acoustic waves to the acoustic wave with the difference frequency f = f 2 − f 1 in the altitude ranges 0-0.1 km, in the strongly nonlinear regime, and (2) of the acoustic wave with the difference frequency to atmospheric acoustic gravity waves with the modulational frequency in the altitude ranges 0.1-20 km, which then reach the altitudes of the ionospheric E and F regions, in a practically linear regime. AGWs, nonlinearly transformed from the sound waves, launched by the two-frequency ground-based sound generator can increase the transparency of the ionosphere for the electromagnetic waves in HF (MHz) and VLF (kHz) ranges. The developed theoretical model can be used for interpreting an active experiment that includes the PSG impact on the atmosphere-ionosphere system, measurements of electromagnetic and acoustic fields, study of the variations in ionospheric transparency for the radio emissions from galactic radio sources, optical measurements, and the impact on atmospheric aerosols. The proposed approach can be useful for better understanding the mechanism of the acoustic channel of seismo-ionospheric coupling.

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Confirmation of existence of the small-scale field-aligned currents in middle and low latitudes and an estimate of time scale of their temporal variation

Cited by 22 publications

References 10 publications

Localized field-aligned currents and 4-min TEC and ground magnetic oscillations during the 2015 eruption of Chile’s Calbuco volcano

Localized field-aligned currents and 4-min TEC and ground magnetic oscillations during the 2015 eruption of Chile’s Calbuco volcano

An initial ULF wave index derived from 2 years of Swarm observations

Ground-based acoustic parametric generator impact on the atmosphere and ionosphere in an active experiment

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