EMIC Wave Properties Associated With and Without Injections in The Inner Magnetosphere

Jun, Chae‐Woo; Yue, Chao; Bortnik, J.; Lyons, L. R.; Nishimura, Y.; Kletzing, C. A.

doi:10.1029/2018ja026279

Cited by 44 publications

(99 citation statements)

References 69 publications

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“…The electron inertial effect allows that the IIHW has dependence on k ⊥ and k ⊥ is finite at the mode conversion location, thereby θ normal becomes less than 90° as shown in Figure b. However, the angle in Figure b is still very close to 90°, while the observed θ normal near the magnetic equator is 30–60° (Jun et al, ; Saikin et al, ).…”

Section: Discussionmentioning

confidence: 96%

“…Electromagnetic ion cyclotron (EMIC) waves are low‐frequency waves typically in the Pc 1‐2 frequency range that are excited below the proton gyrofrequency and are commonly observed in the plasmasphere and magnetosphere (e.g., Allen et al, ; Anderson et al, ; Fraser & McPherron, ; Jun et al, ; Mauk, ; Saikin et al, ; Usanova et al, ; Zhang et al, ). These waves are important in magnetospheric dynamics because they are able to heat ionospheric ions to magnetospheric energies (e.g., André et al, ), regulate pressure anisotropy in the magnetosphere (Anderson et al, ), populate the magnetosphere with energetic heavy ions during substorms, and induce enhanced proton precipitation (Thorne & Horne, ) and can provide a significant loss process for radiation belt electrons (Ukhorskiy et al, ).…”

Section: Introductionmentioning

confidence: 99%

“…The linear polarization has been suggested as results from superposition (Denton et al, ) or as a refraction effect at off‐equator (Kim & Johnson, ). However, linearly polarized EMIC waves are often detected near the wave source region (magnetic equator; e.g., Allen et al, ; Anderson et al, ; Min et al, ; Saikin et al, ; Jun et al, ), and the occurrence rate increases up to 100% in the inner magnetosphere (Saikin et al, ). Therefore, we investigate an alternative scenario where the waves are generated directly via linear mode conversion near the ion‐ion hybrid (IIH) resonance in multi‐ion plasmas (Kim et al, ; Lee et al, ).…”

Section: Introductionmentioning

confidence: 99%

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Electron Inertial Effects on Linearly Polarized Electromagnetic Ion Cyclotron Waves at Earth's Magnetosphere

Kim

Lee

2019

JGR Space Physics

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We discuss a role of the electron inertial effect on linearly polarized electromagnetic ion cyclotron (EMIC) waves at Earth. The linearly polarized EMIC waves have been previously suggested to be generated via mode conversion from the fast compressional wave at the ion-ion hybrid (IIH) resonance. When the electron inertial effects are neglected, the wave normal angle of the mode-converted IIH waves is 90 • because the wave vector perpendicular to the magnetic field becomes infinite at the IIH resonance. When the electron inertial effect is considered, the mode-converted IIH waves can propagate across the magnetic field lines, and the wavelength perpendicular to the magnetic field approaches the electron inertial length scale near the Buchsbaum resonance. These waves are referred to as electron inertial waves. Due to the electron inertial effect, the perpendicular wave number to the ambient magnetic field near the IIH resonance remains finite, and the wave normal angle is less than 90 • . The wave normal angle where the maximum absorption occurs in a dipole magnetic field is 30-80 • , which is consistent with the observed values near the magnetic equator. Therefore, the numerical results suggest that the linearly polarized EMIC wave generated via mode conversion near the IIH resonance can be detected in between the Buchsbaum and the IIH resonance frequencies, and these waves can have normal angle less than 90 • . Key Points:• Mode-converted ion-ion hybrid waves can propagate toward the Buchsbaum resonance due to the electron inertial effects • Electron inertial effects allow the mode-converted ion-ion hybrid waves have medium normal angle less than 90 • • Linearly polarized EMIC waves generated via mode conversion can have relatively small normal angle between 30 and 80 •

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Section: Discussionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Electron Inertial Effects on Linearly Polarized Electromagnetic Ion Cyclotron Waves at Earth's Magnetosphere

Kim

Lee

2019

JGR Space Physics

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“…EMIC waves have been widely statistically studied in many previous works (Allen et al, ; Jun et al, , ; Meredith et al, ; Min et al, ; Saikin et al, ). However, due to the limited spatial coverage for one satellite, we need to combine the statistical results based on various satellites to get a comprehensive and reliable EMIC wave model in the Earth's magnetosphere.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

“…Moreover, they also pointed out the occurrence peak of O + band EMIC waves is in the morning sector. Another statistical study of EMIC waves in the inner magnetosphere with Van Allen Probes data was preformed by Jun et al (, ), which mainly focused on the relationship between EMIC waves and particle injections.…”

Section: Introductionmentioning

confidence: 99%

Analyzing EMIC Waves in the Inner Magnetosphere Using Long‐Term Van Allen Probes Observations

Chen

Gao

et al. 2019

JGR Space Physics

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With 64‐month magnetic data from Van Allen Probes, we have studied not only the global distribution, wave normal angle (θ), and ellipticity (ε) of electromagnetic ion cyclotron (EMIC) waves, but also the dependence of their occurrence rates and magnetic amplitudes on the AE* index (the mean value of AE index over previous 1 hr). Our results show that H+ band waves are preferentially detected at 5 ≤ L ≤ 6.5, in the noon sector. They typically have small θ (<30°) and weakly left‐hand polarization but become more oblique and linearly polarized at larger magnetic latitudes or L‐shells. With the increase of AE* index, their occurrence rate significantly increases in the noon sector, and their source region extends to dusk sector. He+ band waves usually occur in the predawn and morning sectors at 3 ≤ L ≤ 4.5. They generally have moderate θ (30 ° − 40°) and left‐hand polarization and also become more oblique and linearly polarized at larger latitudes or L‐shells. There is a clear enhancement of occurrence rate and amplitude during active geomagnetic periods, especially in the dusk and evening sectors. O+ band waves mainly occur at 3 ≤ L ≤ 4 in the predawn sector. They have either very small θ (<20°) or very large θ (>50°), and typically linear or weakly right‐hand polarization. During active periods, they mostly occur at the midnight sector and L < 3.5. As a valuable supplement to previous statistical studies, our result provides not only a more compresentive EMIC wave model for evaluating their effects on the radiation belt, but also detailed observational constraints on generation mechanisms of EMIC waves.

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Statistical Study of EMIC Waves and Related Proton Distributions Observed by the Arase Satellite

Jun

Miyoshi

Nakamura

et al. 2022

Preprint

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We performed a statistical study of electromagnetic ion cyclotron (EMIC) wave distributions and their coupling with energetic protons in the inner magnetosphere using the Arase satellite data from May 2017 to December 2020. We investigated the energetic proton pitch-angle distributions and partial thermal pressures associated with EMIC waves using inter-calibrated proton data in the energy range of 30 eV/q-187 keV/q. With a cold plasma approximation, we computed the proton minimum resonance energies using the observed EMIC wave frequency and plasma density values. We found that the EMIC waves had left-handed polarization near the magnetic equator close to the threshold of proton cyclotron instability, and propagated to higher latitudes along the field line with polarization reversal. H-EMIC waves showed two peak occurrence regions in the morning and noon sectors at L=7.5-9 outside the plasmasphere. The flux enhancements associated with morning side H-EMIC waves appeared at E<1 keV/q among all pitch angles, while H-EMIC waves in the noon sector exhibited flux enhancement in field-aligned directions at E=1-100 keV/q. He-EMIC waves showed a broad occurrence region from 12 to 20 magnetic local time at L=5.5-8.5 inside the plasmasphere with strong flux enhancements at all pitch-angle ranges at E=1-100 keV/q. The proton minimum resonance energy using the obtained central frequency was consistent with the observed flux enhancements at different peak occurrence regions. We conclude that the free energy sources of EMIC waves in different geomagnetic environments drive the two different types of EMIC waves, and they interact with energetic protons at different energy ranges.

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EMIC Wave Properties Associated With and Without Injections in The Inner Magnetosphere

Cited by 44 publications

References 69 publications

Electron Inertial Effects on Linearly Polarized Electromagnetic Ion Cyclotron Waves at Earth's Magnetosphere

Electron Inertial Effects on Linearly Polarized Electromagnetic Ion Cyclotron Waves at Earth's Magnetosphere

Analyzing EMIC Waves in the Inner Magnetosphere Using Long‐Term Van Allen Probes Observations

Statistical Study of EMIC Waves and Related Proton Distributions Observed by the Arase Satellite

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