| 1. |
- Kataoka, Ryuho, et al.
(author)
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Compound auroral micromorphology : ground-based high-speed imaging
- 2015
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In: EARTH PLANETS AND SPACE. - : Springer Science and Business Media LLC. - 1880-5981. ; 67
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Journal article (peer-reviewed)abstract
- Auroral microphysics still remains partly unexplored. Cutting-edge ground-based optical observations using scientific complementary metal-oxide semiconductor (sCMOS) cameras recently enabled us to observe the fine-scale morphology of bright aurora at magnetic zenith for a variety of rapidly varying features for long uninterrupted periods. We report two interesting examples of combinations of fine-scale rapidly varying auroral features as observed by the sCMOS cameras installed at Poker Flat Research Range (PFRR), Alaska, in February 2014. The first example shows that flickering rays and pulsating modulation simultaneously appeared at the middle of a surge in the pre-midnight sector. The second example shows localized flickering aurora associated with growing eddies at the poleward edge of an arc in the midnight sector.
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| 2. |
- Kim, Hyangpyo, et al.
(author)
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Ionospheric Plasma Density Oscillation Related to EMIC Pc1 Waves
- 2020
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In: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 47:15
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Journal article (peer-reviewed)abstract
- We report the first observation of plasma density oscillations coherent with magnetic Pc1 waves. Swarm satellites observed compressional Pc1 wave activity in the 0.5-3 Hz band, which was coherent with in situ plasma density oscillations. Around the Pc1 event location, the Antarctic Neumayer Station III (L similar to 4.2) recorded similar Pc1 events in the horizontal component while NOAA-15 observed isolated proton precipitations at energies above 30 keV. All these observations support that the compressional Pc1 waves at Swarm are oscillations converted from electromagnetic ion cyclotron (EMIC) waves coming from the magnetosphere. The magnetic field and plasma density oscillate in-phase. We compared the amplitudes of density and magnetic field oscillations normalized to background values and found that the density power is much larger than the magnetic field power. This difference cannot be explained by a simple magnetohydrodynamic (MHD) model, although steep horizontal/vertical gradients of background ionospheric density can partly reconcile the discrepancy.
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| 3. |
- Kim, Hyangpyo, et al.
(author)
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Isolated Proton Aurora Driven by EMIC Pc1 Wave : PWING, Swarm, and NOAA POES Multi-Instrument Observations
- 2021
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In: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 48:18
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Journal article (peer-reviewed)abstract
- We report the concurrent observations of F-region plasma changes and field-aligned currents (FACs) above isolated proton auroras (IPAs) associated with electromagnetic ion cyclotron Pc1 waves. Key events on March 19, 2020 and September 12, 2018 show that ground magnetometers and all-sky imagers detected concurrent Pc1 wave and IPA, during which NOAA POES observed precipitating energetic protons. In the ionospheric F-layer above the IPA zone, the Swarm satellites observed transverse Pc1 waves, which span wider latitudes than IPA. Around IPA, Swarm also detected the bipolar FAC and localized plasma density enhancement, which is occasionally surrounded by wide/shallow depletion. This indicates that wave-induced proton precipitation contributes to the energy transfer from the magnetosphere to the ionosphere.
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| 4. |
- Kim, Hyangpyo, et al.
(author)
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Statistical Analysis of Pc1 Wave Ducting Deduced From Swarm Satellites
- 2021
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In: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 126:3
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Journal article (peer-reviewed)abstract
- Transverse Pc1 waves propagating from magnetospheric source regions undergo mode conversion to the compressional mode in the ionosphere due to the induced Hall current. Mode converted Pc1 waves propagate across the magnetic field through the ionospheric waveguide. This process is called Pc1 wave ducting (PWD). PWDs have been observed by magnetometers on both ground and low Earth orbit satellites over a wide latitudinal and longitudinal range. In this work, we present the statistical analysis results of PWD exploiting Swarm satellites from 2015 to 2019. Spatial distributions show that the PWDs are mainly observed over the South Atlantic Anomaly longitudes, possibly due to the high Hall conductivity and F-region density, and at subauroral/auroral latitudes (+/- 50 degrees-70 degrees MLAT). The occurrence rate of PWD increases with increasing AE and |SYM-H| indices. Seasonal dependence shows that PWD exhibits a high occurrence rate during equinox and local summer while local winter hosts only a low occurrence. The asymmetry between summer and winter can be explained by the ionospheric plasma density. The high occurrence rate in equinox may result from intense geomagnetic activity during the equinox, probably due to the Russell-McPherron effect. From our statistical analysis, we conclude that the occurrence of PWD is controlled by both ionospheric plasma conditions and geomagnetic activity, and that the mode conversion and PWD occur more efficiently as plasma density increases.
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| 5. |
- Oyama, Shin-ichiro, et al.
(author)
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Auroral molecular-emission effects on the atomic oxygen line at 777.4 nm
- 2018
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In: Earth Planets and Space. - : SPRINGEROPEN. - 1343-8832 .- 1880-5981. ; 70
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Journal article (peer-reviewed)abstract
- One of the representative auroral emission lines that radiates from F-region heights and is measurable on the ground is the 777.4nm line from excited atomic oxygen. This line has been adopted, along with another E-region emission line, for example 427.8nm, to estimate the mean energy and total energy flux of precipitating auroral electrons. The influence of emissions from part of the molecular nitrogen band, which mainly radiate from E-region heights, should be carefully evaluated because it might overlap the 777.4nm atomic oxygen line in the spectrum. We performed statistical analysis of auroral spectrograph measurements that were obtained during the winter of 2016-2017 in TromsO, Norway, to derive the ratio of the intensity of the 777.4nm atomic oxygen line to that of the net measurement through a typically used optical filter with a full width at half maximum of a few nm. The ratio had a negative trend against geomagnetic activity, with a primary distribution of 0.5-0.7 and a minimum value of 0.3 for the most active auroral condition in this study. This result suggests that the 30-50% emission intensities measured through the optical filter may be from the molecular nitrogen band.
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