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Found 202 entries in the Bibliography.
Showing entries from 1 through 50
| 2021 |
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Inter-calibrated Measurements of Intense Whistlers by Arase and Van Allen Probes Abstract Measurements of electromagnetic waves in space plasmas are an important tool for our understanding of physical processes in this environment. Inter-calibration of data from different spacecraft missions is necessary for combining their measurements in empirical models or in case studies. We show results collected during a close conjunction of the Van Allen Probes and Arase spacecraft. The inter-calibration is based on a fortuitous case of common observations of strong whistlers at frequencies between a few hundred hertz and 10 kHz, which are generated by the same lightning strokes and which propagate along very similar paths to the two spacecraft. Measured amplitudes of the magnetic field fluctuations are the same within ∼14\% precision of our analysis, corresponding to 1.2 dB. Currently archived electric field measurements show twice larger amplitudes on Arase compared to Van Allen Probes but they start to match within ∼33\% precision (2.5 dB) once the newest results on the interface of the antennas to the surrounding plasma are included in the calibration procedures. Ray tracing simulations help us to build a consistent scenario of wave propagation to both spacecraft reflected by a successful inter-calibration of the polarization and propagation parameters obtained from multicomponent measurements. We succeed in linking the spacecraft observations to localizations of lightning return strokes by two different ground based networks which independently verify the correctness of the Universal Time tags of waveform measurements by both spacecraft missions, with an uncertainty better than 10 ms. This article is protected by copyright. All rights reserved. Santolik, O.; Miyoshi, Y.; Kolmašová, I.; Matsuda, S.; Hospodarsky, G.; Hartley, D.; Kasahara, Y.; Kojima, H.; Matsuoka, A.; Shinohara, I.; Kurth, W.; Kletzing, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029700 calibration of measeurements of electromagnetic waves; Whistlers; ducts; Van Allen Probes |
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Electromagnetic power of lightning superbolts from Earth to space Lightning superbolts are the most powerful and rare lightning events with intense optical emission, first identified from space. Superbolt events occurred in 2010-2018 could be localized by extracting the high energy tail of the lightning stroke signals measured by the very low frequency ground stations of the World-Wide Lightning Location Network. Here, we report electromagnetic observations of superbolts from space using Van Allen Probes satellite measurements, and ground measurements, and with two events measured both from ground and space. From burst-triggered measurements, we compute electric and magnetic power spectral density for very low frequency waves driven by superbolts, both on Earth and transmitted into space, demonstrating that superbolts transmit 10-1000 times more powerful very low frequency waves into space than typical strokes and revealing that their extreme nature is observed in space. We find several properties of superbolts that notably differ from most lightning flashes; a more symmetric first ground-wave peak due to a longer rise time, larger peak current, weaker decay of electromagnetic power density in space with distance, and a power mostly confined in the very low frequency range. Their signal is absent in space during day times and is received with a long-time delay on the Van Allen Probes. These results have implications for our understanding of lightning and superbolts, for ionosphere-magnetosphere wave transmission, wave propagation in space, and remote sensing of extreme events. Ripoll, J.-F.; Farges, T.; Malaspina, D.; Cunningham, G.; Lay, E.; Hospodarsky, G.; Kletzing, C.; Wygant, J.; Published by: Nature Communications Published on: 06/2021 YEAR: 2021 DOI: https://doi.org/10.1038/s41467-021-23740-6 |
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Abstract We performed a comprehensive statistical study of electromagnetic ion cyclotron (EMIC) waves observed by the Van Allen Probes and Exploration of energization and Radiation in Geospace satellite (ERG/Arase). From 2017 to 2018, we identified and categorized EMIC wave events with respect to wavebands (H+ and He+ EMIC waves) and relative locations from the plasmasphere (inside and outside the plasmasphere). We found that H+ EMIC waves in the morning sector at L>8 are predominantly observed with a mixture of linear and right-handed polarity and higher wave normal angles during quiet geomagnetic conditions. Both H+ and He+ EMIC waves observed in the noon sector at L∼4-6 have left-handed polarity and lower wave normal angles at |MLAT|< 20˚ during the recovery phase of a storm with moderate solar wind pressure. In the afternoon sector (12-18 MLT), He+ EMIC waves are dominantly observed with strongly enhanced wave power at L∼6-8 during the storm main phase, while in the dusk sector (17-21 MLT) they have lower wave normal angles with linear polarity at L>8 during geomagnetic quiet conditions. Based on distinct characteristics at different EMIC wave occurrence regions, we suggest that EMIC waves in the magnetosphere can be generated by different free energy sources. Possible sources include the freshly injected particles from the plasma sheet, adiabatic heating by dayside magnetospheric compressions, suprathermal proton heating by magnetosonic waves, and off-equatorial sources. This article is protected by copyright. All rights reserved. Jun, C.-W; Miyoshi, Y.; Kurita, S.; Yue, C.; Bortnik, J.; Lyons, L.; Nakamura, S.; Shoji, M.; Imajo, S.; Kletzing, C.; Kasahara, Y.; Kasaba, Y.; Matsuda, S.; Tsuchiya, F.; Kumamoto, A.; Matsuoka, A.; Shinohara, I.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2020JA029001 Spatial distributions of EMIC waves; RBSP and Arase observations; EMIC wave properties; EMIC wave dependence on geomagnetic condition; Van Allen Probes |
| 2020 |
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Whistler mode chorus waves have recently been established as the most likely candidate for scattering relativistic electrons to produce the electron microbursts observed by low altitude satellites and balloons. These waves would have to propagate from the equatorial source region to significantly higher magnetic latitude in order to scatter electrons of these relativistic energies. This theoretically proposed propagation has never been directly observed. We present the first direct observations of the same discrete rising tone chorus elements propagating from a near equatorial (Van Allen Probes) to an off-equatorial (Arase) satellite. The chorus is observed first on the more equatorial satellite and is found to be more oblique and significantly attenuated at the off-equatorial satellite. This is consistent with the prevailing theory of chorus propagation and with the idea that chorus must propagate from the equatorial source region to higher latitudes. Ray tracing of chorus at the observed frequencies confirms that these elements could be generated parallel to the field at the equator, and propagate through the medium unducted to Van Allen Probes A and then to Arase with the observed time delay, and have the observed obliquity and intensity at each satellite. Colpitts, Chris; Miyoshi, Yoshizumi; Kasahara, Yoshiya; Delzanno, Gian; Wygant, John; Cattell, Cynthia; Breneman, Aaron; Kletzing, Craig; Cunningham, Greg; Hikishima, Mitsuru; Matsuda, Shoya; Katoh, Yuto; Ripoll, Jean-Francois; Shinohara, Iku; Matsuoka, Ayako; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028315 Chorus; wave; propagation; Simultaneous observations; Radiation belt; Van Allen Probes |
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Recent availability of a considerable amount of satellite and ground-based data has allowed us to analyze rare conjugated events where extremely low and very low frequency waves from the same source region are observed in different locations. Here, we report a quasiperiodic (QP) emission, showing one-to-one correspondence, observed by three satellites in space (Arase and the Van Allen Probes) and a ground station. The main event was on 29 November 2018 from 12:06 to 13:08 UT during geomagnetically quiet times. Using the position of the satellites we estimated the spatial extent of the area where the one-to-one correspondence is observed. We found this to be up to 1.21 Earth s radii by 2.26 hr MLT, in radial and longitudinal directions, respectively. Using simple ray tracing calculations, we discuss the probable source location of these waves. At ∼12:20 UT, changes in the frequency sweep rate of the QP elements are observed at all locations associated with magnetic disturbances. We also discuss temporal changes of the spectral shape of QP observed simultaneously in space and on the ground, suggesting the changes are related to properties of the source mechanisms of the waves. This could be linked to two separate sources or a larger source region with different source intensities (i.e., electron flux). At frequencies below the low hybrid resonance, waves can experience attenuation and/or reflection in the magnetosphere. This could explain the sudden end of the observations at the spacecraft, which are moving away from the area where waves can propagate. Martinez-Calderon, C.; Němec, F.; Katoh, Y.; Shiokawa, K.; Kletzing, C.; Hospodarsky, G.; Santolik, O.; Kasahara, Y.; Matsuda, S.; Kumamoto, A.; Tsuchiya, F.; Matsuoka, A.; Shoji, M.; Teramoto, M.; Kurita, S.; Miyoshi, Y.; Ozaki, M.; Nishitani, N.; Oinats, A.; Kurkin, V.; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028126 VLF/ELF; spatial extent; conjugated events; ERG; RBSP; quasiperiodic emissions; Van Allen Probes |
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Whistler mode chorus waves can scatter plasma sheet electrons into the loss cone and produce the Earth s diffuse aurora. Van Allen Probes observed plasma sheet electron injections and intense chorus waves on 24 November 2012. We use quasilinear theory to calculate the precipitating electron fluxes, demonstrating that the chorus waves could lead to high differential energy fluxes of precipitating electrons with characteristic energies of 10–30 keV. Using this method, we calculate the precipitating electron flux from 2012 to 2019 when the Van Allen Probes were near the magnetic equator and perform global surveys of electron precipitation under different geomagnetic conditions. The most significant electron precipitation due to chorus is found from the nightside to dawn sectors over 4 < L < 6.5. The average total precipitating energy flux is enhanced during disturbed conditions, with time-averaged values reaching ~3–10 erg/cm2/s when AE ≥ 500 nT. Ma, Q.; Connor, H.; Zhang, X.-J.; Li, W.; Shen, X.-C.; Gillespie, D.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Claudepierre, S.; Reeves, G.; Spence, H.; Published by: Geophysical Research Letters Published on: 07/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020GL088798 Chorus wave; electron precipitation; plasma sheet electron; Van Allen Probes observation; Van Allen Probes |
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Abstract On 22 December 2015, the two Van Allen Probes observed two sets of electromagnetic ion cyclotron (EMIC) wave bursts during a close conjunction when both Probe A and Probe B were separated by 0.57 to 0.68 RE. The EMIC waves occurred during an active period in the recovery phase of a coronal mass ejection-driven geomagnetic storm. Both spacecraft observed EMIC wave bursts that had similar spatial structure within a 1–2 min time delay. The EMIC waves occurred outside the plasmasphere, within ΔL ≈ 1–2 of the plasmapause and within a few degrees in magnetic latitude of the equatorial plane. The spatial structure of the EMIC wave bursts may have been related to the proton drift paths outside the plasmasphere and influenced by total magnetic field strength variations associated with solar wind pressure enhancements. The EMIC waves were observed in a narrow L shell region from L ≈ 4.55–5.32 between 10 and 11 magnetic local time (MLT) on the outbound halves of the spacecraft orbits and from L ≈ 4.82–5.51 between 13 and 14 MLT on the inbound halves of the spacecraft orbits. However, Pc1 pulsations were observed on the ground over a broad range of local times. The anisotropy of the proton pitch angle distributions was enhanced when the EMIC waves were observed. Although the overall radiation belt response during this storm was dominated by acceleration and transport processes, the EMIC waves produced local pitch angle scattering of 13–15 keV protons and 2.1–2.6 MeV electrons, consistent with calculations of the expected resonant energies. Sigsbee, K.; Kletzing, C. A.; Faden, J.; Jaynes, A. N.; Reeves, G.; Jahn, J.-M.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2020 YEAR: 2020 DOI: 10.1029/2019JA027424 EMIC waves; Plasmapause; Proton Anisotropy; Storm Recovery Phase; Van Allen Probes; pitch angle scattering |
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On 22 December 2015, the two Van Allen Probes observed two sets of electromagnetic ion cyclotron (EMIC) wave bursts during a close conjunction when both Probe A and Probe B were separated by 0.57 to 0.68 RE. The EMIC waves occurred during an active period in the recovery phase of a coronal mass ejection-driven geomagnetic storm. Both spacecraft observed EMIC wave bursts that had similar spatial structure within a 1–2 min time delay. The EMIC waves occurred outside the plasmasphere, within ΔL ≈ 1–2 of the plasmapause and within a few degrees in magnetic latitude of the equatorial plane. The spatial structure of the EMIC wave bursts may have been related to the proton drift paths outside the plasmasphere and influenced by total magnetic field strength variations associated with solar wind pressure enhancements. The EMIC waves were observed in a narrow L shell region from L ≈ 4.55–5.32 between 10 and 11 magnetic local time (MLT) on the outbound halves of the spacecraft orbits and from L ≈ 4.82–5.51 between 13 and 14 MLT on the inbound halves of the spacecraft orbits. However, Pc1 pulsations were observed on the ground over a broad range of local times. The anisotropy of the proton pitch angle distributions was enhanced when the EMIC waves were observed. Although the overall radiation belt response during this storm was dominated by acceleration and transport processes, the EMIC waves produced local pitch angle scattering of 13–15 keV protons and 2.1–2.6 MeV electrons, consistent with calculations of the expected resonant energies. Sigsbee, K.; Kletzing, C. A.; Faden, J.; Jaynes, A. N.; Reeves, G.; Jahn, J.-M.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2019JA027424 EMIC waves; Plasmapause; Proton Anisotropy; Storm Recovery Phase; Van Allen Probes; pitch angle scattering |
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A Multi-Instrument Approach to Determining the Source-Region Extent of EEP-Driving EMIC Waves Abstract Recent years have seen debate regarding the ability of electromagnetic ion cyclotron (EMIC) waves to drive EEP (energetic electron precipitation) into the Earth s atmosphere. Questions still remain regarding the energies and rates at which these waves are able to interact with electrons. Many studies have attempted to characterize these interactions using simulations; however, these are limited by a lack of precise information regarding the spatial scale size of EMIC activity regions. In this study we examine a fortuitous simultaneous observation of EMIC wave activity by the RBSP-B and Arase satellites in conjunction with ground-based observations of EEP by a subionospheric VLF network. We describe a simple method for determining the longitudinal extent of the EMIC source region based on these observations, calculating a width of 0.75 hr MLT and a drift rate of 0.67 MLT/hr. We describe how this may be applied to other similar EMIC wave events. Hendry, A.; Santolik, O.; Miyoshi, Y.; Matsuoka, A.; Rodger, C.; Clilverd, M.; Kletzing, C.; Shoji, M.; Shinohara, I.; Published by: Geophysical Research Letters Published on: 03/2020 YEAR: 2020 DOI: 10.1029/2019GL086599 EMIC waves; electron precipitation; subionospheric VLF; Van Allen Probes; AARDDVARK; Arase |
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Fine Harmonic Structure of Equatorial Noise with a Quasiperiodic Modulation Abstract Equatorial noise emissions (fast magnetosonic waves) are electromagnetic waves observed routinely in the equatorial region of the inner magnetosphere. They propagate with wave vectors nearly perpendicular to the ambient magnetic field; that is, they are limited to frequencies below the lower hybrid frequency. The waves are generated by instabilities of ring-like proton distribution functions, which result in their fine harmonic structure with intensity maxima close to harmonics of the proton cyclotron frequency in the source region. Although most equatorial noise emissions are continuous in time, some events exhibit a clear quasiperiodic time modulation of the wave intensity, with typical modulation periods on the order of minutes. We analyze 72 such events (17 observed by the Cluster spacecraft, 55 observed by the Van Allen Probes spacecraft) for which high-resolution data were available. The analysis of the observed harmonic structure allows us to determine source radial distances of the events. It is found that the calculated source radial distances are generally close to the radial distances where the events were observed. The harmonic numbers where the events are generated range between about 12 and 30. Two events for which the spacecraft passed through the generation region were identified and analyzed. No simultaneous ultra-low-frequency magnetic field pulsations and no periodic plasma number density variations were observed. Although the in situ measured proton distribution functions were shown to be responsible for the wave growth, an insufficient resolution of the particle instruments prevented us from detecting a quasiperiodic modulation possibly present in the particle data. Němec, F.; Tomori, A.; Santolik, O.; Boardsen, S.; Hospodarsky, G.; Kurth, W.; Pickett, J.; Kletzing, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2020 YEAR: 2020 DOI: 10.1029/2019JA027509 equatorial noise; Fast Magnetosonic Waves; quasiperiodic modulation; Van Allen Probes |
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Abstract We provide a statistical analysis of both electric and magnetic field wave amplitudes of very low frequency lightning-generated waves (LGWs) based on the equivalent of 11.5 years of observations made by the Van Allen Probes encompassing ~24.6 × 106 survey mode measurements. We complement this analysis with data from the ground-based World Wide Lightning Location Network to explore differences between satellite and ground-based measurements. LGW mean amplitudes are found to be low compared with other whistler mode waves (1 ± 1.6 pT and 19 ± 59 μV/m). Extreme events (1/5,000) can reach 100 pT and contributes strongly to the mean power below L = 2. We find excellent correlations between World Wide Lightning Location Network-based power and wave amplitudes in space at various longitudes. We reveal strong dayside ionospheric damping of the LGW electric field. LGW amplitudes drop for L < 2, contrary to the Earth s intense equatorial lightning activity. We conclude that it is difficult for equatorial LGW to propagate and remain at L < 2. Ripoll, J.-F.; Farges, T.; Malaspina, D.; Lay, E.; Cunningham, G.; Hospodarsky, G.; Kletzing, C.; Wygant, J.; Published by: Geophysical Research Letters Published on: 03/2020 YEAR: 2020 DOI: 10.1029/2020GL087503 lightning-generated waves; electric wave power; magnetic wave power; WWLLN database; Radiation belts; Van Allen Probes |
| 2019 |
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On 23 February 2014, Van Allen Probes sensors observed quite strong electromagnetic ion cyclotron (EMIC) waves in the outer dayside magnetosphere. The maximum amplitude was more than 14 nT, comparable to 7\% of the magnitude of the ambient magnetic field. The EMIC waves consisted of a series of coherent rising tone emissions. Rising tones are excited sporadically by energetic protons. At the same time, the probes detected drastic fluctuations in fluxes of MeV electrons. It was found that the electron fluxes decreased by more than 30\% during the 1 min following the observation of each EMIC rising tone emissions. Furthermore, it is concluded that the flux reduction is a nonadiabatic (irreversible) process since holes in the particle flux levels appear as drift echoes with energy dispersion. We examine the process of electron pitch angle scattering by nonlinear wave trapping due to anomalous cyclotron resonance with EMIC rising tone emissions. The energy range of precipitated electrons agrees with the presumed energy for the threshold amplitude for nonlinear wave trapping. This is the first report of rapid precipitation (<1 min) of relativistic electrons by EMIC rising tone emissions and their drift echoes in time observed by spacecraft. Nakamura, S.; Omura, Y.; Kletzing, C.; Baker, D.; Published by: Journal of Geophysical Research: Space Physics Published on: May-08-2020 YEAR: 2019 DOI: 10.1029/2019JA026772 EMIC waves; Magnetosphere; microburst; nonlinear; Radiation belt; Van Allen Probes; Wave-particle interaction |
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We investigate the global distribution and provide empirical models of fast magnetosonic waves using the combined observations by the magnetometer and waveform receiver on board Van Allen Probes. The magnetometer measurements of magnetosonic waves indicate a significant wave power within the frequency range from the helium gyrofrequency to 20 Hz at L >= 4 in the afternoon sector, both inside and outside the plasmapause. The waveform receiver measurements indicate a significant wave power from 20 Hz to the lower hybrid resonance frequency at L <= 5.5 near the dayside outside the plasmapause or in the afternoon sector inside the plasmapause. The sum of the wave powers from the two instruments provides the wave power distribution over the complete frequency range. The most significant root-mean-square wave amplitude of magnetosonic waves is typically 100\textendash200 pT inside or outside the plasmapause with a magnetic local time coverage of 30\textendash50\% during geomagnetically active times when AE* > 500 nT. The magnetosonic wave frequency increases with decreasing L shell following the trend of the proton gyrofrequency outside the plasmapause, indicating a close relation with the local wave generation. Inside the plasmapause, the dependence of wave frequency on L shell is weaker, and the wave frequency is more stable across L shells, indicating the wave propagation effects from the source located at higher L shells. We have performed polynomial fits of the global magnetosonic wave distribution and wave frequency spectra, which are useful in future radiation belt simulations. Ma, Q.; Li, W.; Bortnik, J.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2019 YEAR: 2019 DOI: 10.1029/2019JA027407 Empirical Fitting; Global Survey; magnetosonic waves; Van Allen Probes; Van Allen Probes observation |
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Excitation of toroidal mode standing Alfv\ en waves in the midnight sector of the inner magnetosphere in association with substorms is well documented, but studies are sparse on dayside sources for the waves. This paper reports observation of midnight toroidal waves by the Van Allen Probe B spacecraft during a geomagnetically quiet period on 12\textemdash13 May 2013. The spacecraft detected toroidal waves excited at odd harmonics below 30 mHz as it moved within the plasmasphere from ~2100 magnetic local time (MLT) to ~0030 MLT through midnight in the dipole L range 4.2\textemdash6.1. The frequencies and the relationship between the electric and magnetic field components of the waves are consistent with theoretical toroidal waves for a reflecting ionosphere. At the time of the nightside toroidal waves, compressional waves were observed by geostationary satellites located on the dayside, and the amplitudes of both types of waves varied with the cone angle of the interplanetary magnetic field. The nightside toroidal waves were likely driven by fast mode waves that resulted from transmission of upstream ultralow frequency waves into the magnetosphere. Ground magnetometers located near the footprint of the spacecraft did not detect toroidal waves. Takahashi, Kazue; Vellante, Massimo; Del Corpo, Alfredo; Claudepierre, Seth; Kletzing, Craig; Wygant, John; Koga, Kiyokazu; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2019 YEAR: 2019 DOI: 10.1029/2019JA027370 Ion foreshock; Nightside magnetosphere; Toroidal Alfven waves; Van Allen Probe; Van Allen Probes |
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We report the electron flux modulations without corresponding magnetic fluctuations from unique multipoint satellite observations of the Arase (Exploration of Energization and Radiation in Geospace) and the Van Allen Probe (Radiation Belt Storm Probe [RBSP])-B satellites. On 30 March 2017, both Arase and RBSP-B observed periodic fluctuations in the relativistic electron flux with energies ranging from 500 keV to 2 MeV when they were located near the magnetic equator in the morning and dusk local time sectors, respectively. Arase did not observe Pc5 pulsations, while they were observed by RBSP-B. The clear dispersion signature of the relativistic electron fluctuations observed by Arase indicates that the source region is limited to the postnoon to the dusk sector. This is confirmed by RBSP-B and ground-magnetometer observations, where Pc5 pulsations are observed to drift-resonate with relativistic electrons on the duskside. Thus, Arase observed the drift-resonance signatures \textquotedblleftremotely,\textquotedblright whereas RBSP-B observed them \textquotedblleftlocally.\textquotedblright Teramoto, M.; Hori, T.; Saito, S.; Miyoshi, Y.; Kurita, S.; Higashio, N.; Matsuoka, A.; Kasahara, Y.; Kasaba, Y.; Takashima, T.; Nomura, R.; e, Nos\; Fujimoto, A.; Tanaka, Y.-M.; Shoji, M.; Tsugawa, Y.; Shinohara, M.; Shinohara, I.; Blake, J.; Fennell, J.F.; Claudepierre, S.G.; Turner, D.; Kletzing, C.; Sormakov, D.; Troshichev, O.; Published by: Geophysical Research Letters Published on: 11/2019 YEAR: 2019 DOI: 10.1029/2019GL084379 |
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The Storm-Time Ring Current Response to ICMEs and CIRs Using Van Allen Probe Observations Using Van Allen Probe observations of the inner magnetosphere during geomagnetic storms driven by interplanetary coronal mass ejections (ICMEs) and corotating interaction regions (CIRs), we characterize the impact of these drivers on the storm-time ring current development. Using 25 ICME- and 35 CIR-driven storms, we have determined the ring current pressure development during the prestorm, main, early-recovery, and late-recovery storm phases, as a function of magnetic local time, L shell and ion species (H+, He+, and O+) over the 100- to 600-keV energy range. Consistent with previous results, we find that during the storm main phase, most of the ring current pressure in the inner magnetosphere is contributed by particles on open drift paths drifting duskward leading to a strong partial ring current. The largest difference between the ICME and CIR ring current responses during the storm main and early-recovery phases is the difference in the response of the <~55-keV O+ to these drivers. While the H+ pressure response shows similar source and convection patterns for ICME and CIR storms, the O+ pressure response is significantly stronger for ICME storms. The ICME O+ pressure increases more strongly than H+ with decreasing L and peaks at lower L shells than H+. Mouikis, C.; Bingham, S.; Kistler, L.; Farrugia, C.; Spence, H.; Reeves, G.; Gkioulidou, M.; Mitchell, D.; Kletzing, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2019 YEAR: 2019 DOI: 10.1029/2019JA026695 ICME vs CI; R Ion composition; Ring Current Pressure; Storm phases; Van Allen Probes |
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Lightning Contribution to Overall Whistler Mode Wave Intensities in the Plasmasphere Electromagnetic waves generated by lightning propagate into the plasmasphere as dispersed whistlers. They can therefore influence the overall wave intensity in space, which, in turn, is important for dynamics of the Van Allen radiation belts. We analyze spacecraft measurements in low-Earth orbit as well as in high-altitude equatorial region, together with a ground-based estimate of lightning activity. We accumulate wave intensities when the spacecraft are magnetically connected to thunderstorms and compare them with measurements obtained when thunderstorms are absent. We show that strong lightning activity substantially affects the wave intensity in a wide range of L-shells and altitudes. The effect is observed mainly between 500 Hz and 4 kHz, but its frequency range strongly varies with L-shell, extending up to 12 kHz for L lower than 3. The effect is stronger in the afternoon, evening, and night sectors, consistent with more lightning and easier wave propagation through the ionosphere. ahlava, J.; emec, F.; Santolik, O.; a, Kolma\v; Hospodarsky, G.; Parrot, M.; Kurth, W.; Kletzing, C.; Published by: Geophysical Research Letters Published on: 07/2019 YEAR: 2019 DOI: 10.1029/2019GL083918 |
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Electromagnetic ion cyclotron (EMIC) waves and magnetosonic waves are commonly observed in the Earth\textquoterights magnetosphere associated with enhanced ring current activity. Using wave and ion measurements from the Van Allen Probes, we identify clear correlations between the hydrogen- and helium-band EMIC waves with the enhancement of trapped helium and oxygen ion fluxes, respectively. We calculate the diffusion coefficients of different ion species using quasi-linear theory to understand the effects of resonant scattering by EMIC waves. Our calculations indicate that EMIC waves can cause pitch angle scattering loss of several keV to hundreds of keV ions, and heating of tens of eV to several keV helium and oxygen ions by hydrogen- and helium-band EMIC waves, respectively. Moreover, we found that magnetosonic waves can cause the resonant heating of thermal protons. Our study indicates the importance of energy transfer from the EMIC and magnetosonic waves to ions with different species at thermal energies. Ma, Q.; Li, W.; Yue, C.; Thorne, R.; Bortnik, J.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Reeves, G.; Spence, H.; Published by: Geophysical Research Letters Published on: 06/2019 YEAR: 2019 DOI: 10.1029/2019GL083513 electromagnetic ion cyclotron waves; Ion heating; Quasilinear modeling; Resonant interaction in plasmasphere; ring current; Van Allen Probes; Van Allen Probes observation |
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Nonlinear Electron Interaction With Intense Chorus Waves: Statistics of Occurrence Rates A comprehensive statistical analysis on 8 years of lower-band chorus wave packets measured by the Van Allen Probes and THEMIS spacecraft is performed to examine whether, when, and where these waves are above the theoretical threshold for nonlinear resonant wave-particle interaction. We find that \~5\textendash30\% of all chorus waves interact nonlinearly with \~30- to 300-keV electrons possessing equatorial pitch angles of >40\textdegree in the outer radiation belt, especially during disturbed (AE>500 nT) periods with energetic particles associated with injections from the plasma sheet. Such considerable occurrence rates of nonlinear interactions imply that the evolution of energetic electron fluxes should be dominated by nonlinear effects, rather than by quasi-linear diffusion as commonly assumed. We discuss the possible consequences of such a large amount of high-amplitude chorus waves and examine their characteristics that can influence the efficiency of nonlinear wave-particle interactions. Zhang, X.-J.; Mourenas, D.; Artemyev, A.; Angelopoulos, V.; Bortnik, J.; Thorne, R.; Kurth, W.; Kletzing, C.; Hospodarsky, G.; Published by: Geophysical Research Letters Published on: 06/2019 YEAR: 2019 DOI: 10.1029/2019GL083833 chorus waves; Electron acceleration; nonlinear wave particle interaction; THEMIS; Van Allen Probes; wave packet size |
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In this study, rapid loss of relativistic radiation belt electrons at low L* values (2.4\textendash3.2) during a strong geomagnetic storm on 22 June 2015 is investigated along with five possible loss mechanisms. Both the particle and wave data are obtained from the Van Allen Probes. Duskside H+ band electromagnetic ion cyclotron (EMIC) waves were observed during a rapid decrease of relativistic electrons with energy above 5.2 MeV occurring outside the plasmasphere during extreme magnetopause compression. Lower He+ composition and enriched O+ composition are found compared to typical values assumed in other studies of cyclotron resonant scattering of relativistic electrons by EMIC waves. Quantitative analysis demonstrates that even with the existence of He+ band EMIC waves, it is the H+ band EMIC waves that are likely to cause the depletion at small pitch angles and strong gradients in pitch angle distributions of relativistic electrons with energy above 5.2 MeV at low L values for this event. Very low frequency wave activity at other magnetic local time can be favorable for the loss of relativistic electrons at higher pitch angles. An illustrative calculation that combines the nominal pitch angle scattering rate due to whistler mode chorus at high pitch angles with the H+ band EMIC wave loss rate at low pitch angles produces loss on time scale observed at L=2.4\textendash3.2. At high L values and lower energies, radial loss to the magnetopause is a viable explanation. Qin, Murong; Hudson, Mary; Li, Zhao; Millan, Robyn; Shen, Xiaochen; Shprits, Yuri; Woodger, Leslie; Jaynes, Allison; Kletzing, Craig; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2019 YEAR: 2019 DOI: 10.1029/2018JA025726 cold ion composition; EMIC wave; minimum resonant energy; pitch angle diffusion; quasi-linear theory; relativistic electron loss; Van Allen Probes |
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Efficient acceleration of relativistic electrons at Landau resonance with obliquely propagating whistler-mode chorus emissions is confirmed by theory, simulation, and observation. The acceleration is due to the perpendicular component of the wave electric field. We first review theoretical analysis of nonlinear motion of resonant electrons interacting with obliquely propagating whistler-mode chorus. We have derived formulae of inhomogeneity factors for Landau and cyclotron resonances to analyze nonlinear wave trapping of energetic electrons by an obliquely propagating chorus element. We performed test particle simulations to confirm that nonlinear wave trapping by both Landau and cyclotron resonances can take place for a wide range of energies. For an element of large amplitude chorus waves observed by the Van Allen Probes, we have performed detailed analyses of the wave form data based on theoretical framework of nonlinear trapping of resonant electrons. We compare the efficiencies of accelerations by cyclotron and Landau resonances. We find significant acceleration can take place both in Landau and cyclotron resonances. What controls the dynamics of relativistic electrons in the Landau resonance is the perpendicular field components rather than the parallel electric field of the oblique chorus wave. In evaluating the efficiency of nonlinear trapping, we have taken into account variation of the wave trapping potential structure controlled by the inhomogeneity factors. Omura, Yoshiharu; Hsieh, Yi-Kai; Foster, John; Erickson, Philip; Kletzing, Craig; Baker, Daniel; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2019 YEAR: 2019 DOI: 10.1029/2018JA026374 inner magnetosphere; nonlinear process; Radiation belts; relativistic electrons; Van Allen Probes; wave particle interaction; whistler-mode chorus |
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Plasma kinetic theory predicts that sufficiently anisotropic proton distribution will excite electromagnetic ion cyclotron (EMIC) waves, which in turn relax the proton distribution to a marginally stable state creating an upper bound on the relaxed proton anisotropy. Here, using EMIC wave observations and coincident plasma measurements made by Van Allen Probes in the inner magnetosphere, we show that the proton distributions are well constrained by this instability to a marginally stable state. Near the threshold, the probability of EMIC wave occurrence is highest, having left-handed polarization and observed near the magnetic equator with relatively small wave normal angles, indicating that these waves are locally generated. In addition, EMIC waves are distributed in two magnetic local time regions with different intensity. Compared with helium band waves, hydrogen band waves behave similarly except that they are often observed in low-density regions. These results reveal several important features regarding EMIC waves excitation and propagation. Yue, Chao; Jun, Chae-Woo; Bortnik, Jacob; An, Xin; Ma, Qianli; Reeves, Geoffrey; Spence, Harlan; Gerrard, Andrew; Gkioulidou, Matina; Mitchell, Donald; Kletzing, Craig; Published by: Geophysical Research Letters Published on: 04/2019 YEAR: 2019 DOI: 10.1029/2019GL082633 EMIC waves; helium-band; hydrogen-band; plasma beta; proton temperature anisotropy; Van Allen Probes |
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Ion transport from the plasma sheet to the ring current is the main cause of the development of the ring current. Energetic (>150 keV) ring current ions are known to be transported diffusively in several days. A recent study suggested that energetic oxygen ions are transported closer to the Earth than protons due to the diffusive transport caused by a combination of the drift and drift-bounce resonances with Pc 3\textendash5 ultralow frequency waves during the 24 April 2013 magnetic storm. To understand the occurrence conditions of such selective oxygen increase (SOI), we investigate the phase space densities (PSDs) between protons and oxygen ions with the first adiabatic invariants (μ) of 0.1\textendash2.0 keV/nT measured by the Radiation Belt Storm Probes Ion Composition Experiment instrument on the Van Allen Probes at L ~ 3\textendash6 during 90 magnetic storms in 2013\textendash2017. We identified the SOI events in which oxygen PSDs increase while proton PSDs do not increase during a period of ~9 hr (one orbital period). Among the 90 magnetic storms, 33\% were accompanied by the SOI events. Global enhancements of Pc 4 and Pc 5 waves observed by ground magnetometers during the SOI events suggest that radial transport due to combination of the drift-bounce resonance with Pc 4 oscillations and the drift resonance with Pc 5 oscillations can be the cause of SOIs. The contribution of the SOI events to the magnetic storm intensity is roughly estimated to be ~9\% on average. Mitani, K.; Seki, K.; Keika, K.; Gkioulidou, M.; Lanzerotti, L.; Mitchell, D.; Kletzing, C.; Yoshikawa, A.; Obana, Y.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2019 YEAR: 2019 DOI: 10.1029/2018JA026168 Magnetic Storms; Oxygen ions; ring current; Van Allen Probes |
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Electromagnetic ion cyclotron (EMIC) waves can drive precipitation of tens of keV protons and relativistic electrons, and are a potential candidate for causing radiation belt flux dropouts. In this study, we quantitatively analyze three cases of EMIC-driven precipitation, which occurred near the dusk sector observed by multiple Low-Earth-Orbiting (LEO) Polar Operational Environmental Satellites/Meteorological Operational satellite programme (POES/MetOp) satellites. During EMIC wave activity, the proton precipitation occurred from few tens of keV up to hundreds of keV, while the electron precipitation was mainly at relativistic energies. We compare observations of electron precipitation with calculations using quasi-linear theory. For all cases, we consider the effects of other magnetospheric waves observed simultaneously with EMIC waves, namely, plasmaspheric hiss and magnetosonic waves, and find that the electron precipitation at MeV energies was predominantly caused by EMIC-driven pitch angle scattering. Interestingly, each precipitation event observed by a LEO satellite extended over a limited L shell region (ΔL ~ 0.3 on average), suggesting that the pitch angle scattering caused by EMIC waves occurs only when favorable conditions are met, likely in a localized region. Furthermore, we take advantage of the LEO constellation to explore the occurrence of precipitation at different L shells and magnetic local time sectors, simultaneously with EMIC wave observations near the equator (detected by Van Allen Probes) or at the ground (measured by magnetometers). Our analysis shows that although EMIC waves drove precipitation only in a narrow ΔL, electron precipitation was triggered at various locations as identified by POES/MetOp over a rather broad region (up to ~4.4 hr MLT and ~1.4 L shells) with similar patterns between satellites. Capannolo, L.; Li, W.; Ma, Q.; Shen, X.-C.; Zhang, X.-J.; Redmon, R.; Rodriguez, J.; Engebretson, M.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Reeves, G.; Raita, T.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2019 YEAR: 2019 DOI: 10.1029/2018JA026291 EMIC waves; energetic electron precipitation; pitch angle scattering; quasi-linear theory; radiation belts dropouts; Van Allen Probes |
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Whistler mode waves are important for precipitating energetic electrons into Earth\textquoterights upper atmosphere, while the quantitative effect of each type of whistler mode wave on electron precipitation is not well understood. In this letter, we evaluate energetic electron precipitation driven by three types of whistler mode waves: plume whistler mode waves, plasmaspheric hiss, and exohiss observed outside the plasmapause. By quantitatively analyzing three conjunction events between Van Allen Probes and POES/MetOp satellites, together with quasi-linear calculation, we found that plume whistler mode waves are most effective in pitch angle scattering loss, particularly for the electrons from tens to hundreds of keV. Our new finding provides the first direct evidence of effective pitch angle scattering driven by plume whistler mode waves and is critical for understanding energetic electron loss process in the inner magnetosphere. We suggest the effect of plume whistler mode waves be accurately incorporated into future radiation belt modeling. Li, W.; Shen, X.-C.; Ma, Q.; Capannolo, L.; Shi, R.; Redmon, R.; Rodriguez, J.; Reeves, G.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Published by: Geophysical Research Letters Published on: 03/2019 YEAR: 2019 DOI: 10.1029/2019GL082095 electron precipitation; hiss; plasmaspheric plume; Plume wave; Van Allen Probes; whistler mode wave |
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Energy coupling between the solar wind and the Earth\textquoterights magnetosphere can affect the electron population in the outer radiation belt. However, the precise role of different internal and external mechanisms that leads to changes of the relativistic electron population is not entirely known. This paper describes how Ultra Low Frequency (ULF) wave activity during the passage of Alfv\ enic solar wind streams contributes to the global recovery of the relativistic electron population in the outer radiation belt. To investigate the contribution of the ULF waves, we searched the Van Allen Probes data for a period in which we can clearly distinguish the enhancement of electron fluxes from the background. We found that the global recovery that started on September 22, 2014, which coincides with the corotating interaction region preceding a high-speed stream and the occurrence of persistent substorm activity, provides an excellent scenario to explore the contribution of ULF waves. To support our analyses, we employed ground and space-based observational data, global magnetohydrodynamic (MHD) simulations, and calculated the ULF wave radial diffusion coefficients employing an empirical model. Observations show a gradual increase of electron fluxes in the outer radiation belt and a concomitant enhancement of ULF activity that spreads from higher to lower L-shells. MHD simulation results agree with observed ULF wave activity in the magnetotail, which leads to both fast and Alfv\ en modes in the magnetospheric nightside sector. The observations agree with the empirical model and are confirmed by Phase Space Density (PhSD) calculations for this global recovery period. Da Silva, L.; Sibeck, D.; Alves, L.; Souza, V.; Jauer, P.; Claudepierre, S.; Marchezi, J.; Agapitov, O.; Medeiros, C.; Vieira, L.; Wang, C.; Jiankui, S.; Liu, Z.; Gonzalez, W.; Dal Lago, A.; Rockenbach, M.; Padua, M.; Alves, M.; Barbosa, M.; Fok, M.-C.; Baker, D.; Kletzing, C.; Kanekal, S.; Georgiou, M.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2019 YEAR: 2019 DOI: 10.1029/2018JA026184 alfv\ en fluctuations; Earth\textquoterights magnetosphere; high speed stream; Radiation belts; relativistic electron flux; ULF wave; Van Allen Probes |
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This paper presents the first analysis of Van Allen Probes measurements of the cold plasma density and electric field in the inner magnetosphere to show that intervals of strong modulation at the solar rotation period occur in the locations of the outer plasmasphere and plasmapause (~0.7 RE peak-to-peak), in the large-scale electric field (~0.24 mV/m peak-to-peak), and in the cold plasma density (~250 cm-3 \textendash ~70 cm-3 peak-to-peak). Solar rotation modulation of the inner magnetosphere is more apparent in the declining phase of the solar cycle than near solar maximum. The periodicities in these parameters are compared to solar EUV irradiance, solar wind dawn-dusk electric field, and Kp. The variations in the plasmapause location at the solar rotation period anti-correlate with solar wind electric field, magnetospheric electric field, and Kp, but not with EUV irradiance, indicating that convective erosion is the dominant physical process controlling the plasmapause at these timescales. Thaller, S.; Wygant, J.; Cattell, C.; Breneman, A.; Tyler, E.; Tian, S.; Engel, A.; De Pascuale, S.; Kurth, W.; Kletzing, C.; Tears, J.; Malaspina, David; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2019 YEAR: 2019 DOI: 10.1029/2018JA026365 convection electric field; inner magnetosphere; Plasmapause; plasmasphere; solar rotation; Van Allen Probes |
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Using observations from the Van Allen Probes EMFISIS instrument, coupled with ray tracing simulations, we determine the fraction of chorus wave power with the conditions required to access the plasmasphere and evolve into plasmaspheric hiss. It is found that only an extremely small fraction of chorus occurs with the required wave vector orientation, carrying only a small fraction of the total chorus wave power. The exception is on the edge of plasmaspheric plumes, where strong azimuthal density gradients are present. In these cases, up to 94\% of chorus wave power exists with the conditions required to access the plasmasphere. As such, we conclude that strong azimuthal density gradients are actually a requirement if a significant fraction of chorus wave power is to enter the plasmasphere and be a source of plasmaspheric hiss. This result suggests it is unlikely that chorus directly contributes a significant fraction of plasmaspheric hiss wave power. Hartley, D.; Kletzing, C.; Chen, L.; Horne, R.; ik, O.; Published by: Geophysical Research Letters Published on: 02/2019 YEAR: 2019 DOI: 10.1029/2019GL082111 chorus waves; EMFISIS; Plasmaspheric Hiss; plasmaspheric plumes; Van Allen Probes; wave normal angle |
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Low-Energy ( The heavy ion component of the low-energy (eV to hundreds of eV) ion population in the inner magnetosphere, also known as the O+ torus, is a crucial population for various aspects of magnetospheric dynamics. Yet even though its existence has been known since the 1980s, its formation remains an open question. We present a comprehensive study of a low-energy ( Gkioulidou, Matina; Ohtani, S.; Ukhorskiy, A; Mitchell, D.; Takahashi, K.; Spence, H.; Wygant, J.; Kletzing, C.; Barnes, R.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2019 YEAR: 2019 DOI: 10.1029/2018JA025862 |
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Properties of Whistler Mode Waves in Earth\textquoterights Plasmasphere and Plumes Whistler mode wave properties inside the plasmasphere and plumes are systematically investigated using 5-year data from Van Allen Probes. The occurrence and intensity of whistler mode waves in the plasmasphere and plumes exhibit dependences on magnetic local time, L, and AE. Based on the dependence of the wave normal angle and Poynting flux direction on L shell and normalized wave frequency to electron cyclotron frequency (fce), whistler mode waves are categorized into four types. Type I: ~0.5 fce with oblique wave normal angles mostly in plumes; Type II: 0.01\textendash0.5 fce with small wave normal angles in the outer plasmasphere or inside plumes; Type III: <0.01 fce with oblique wave normal angles mostly within the plasmasphere or plumes; Type IV: 0.05\textendash0.5 fce with oblique wave normal angles deep inside the plasmasphere. The Poynting fluxes of Type I and II waves are mostly directed away from the equator, suggesting local amplification, whereas the Poynting fluxes of Type III and IV are directed either away from or toward the equator, and may originate from other source regions. Whistler mode waves in plumes have relatively small wave normal angles with Poynting flux mostly directed away from the equator and are associated with high electron fluxes from ~30 keV to hundreds of keV, all of which support local amplification. Whistler mode wave amplitudes in plumes can be stronger than typical plasmaspheric hiss, particularly during active times. Our results provide critical insights into understanding whistler mode wave generation inside the plasmasphere and plumes. Shi, Run; Li, Wen; Ma, Qianli; Green, Alex; Kletzing, Craig; Kurth, William; Hospodarsky, George; Claudepierre, Seth; Spence, Harlan; Reeves, Geoff; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2019 YEAR: 2019 DOI: 10.1029/2018JA026041 Plasmaspheric Hiss; plasmaspheric plume; Van Allen Probes; whistler mode waves |
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To understand the relationship between generation of electromagnetic ion cyclotron (EMIC) waves and energetic particle injections, we performed a statistical study of EMIC waves associated with and without injections based on the Van Allen Probes (Radiation Belt Storm Probes) and Geostationary Operational Environmental Satellite (GOES; GOES-13 and GOES-15) observations. Using 47 months of observations, we identified wave events seen by the Van Allen Probes relative to the plasmapause and to energetic particle injections seen by GOES-13 and GOES-15 on the nightside. We separated the events into four categories: EMIC waves with (without) injections inside (outside) the plasmasphere. We found that He+ EMIC waves have higher occurrence rate inside the plasmasphere, while H+ EMIC waves predominantly occur outside the plasmasphere. Meanwhile, the time duration and peak occurrence rate of EMIC waves associated with injections are shorter and limited to a narrower magnetic local time region than those without injections, indicating that these waves have localized source regions. He+ EMIC waves inside the plasmasphere associated with injection are usually accompanied by an increase in H+ flux within energies of 1\textendash50 keV through all magnetic local time regions, while most wave events outside the plasmasphere show less relationship with H+ flux increase. From these observations, we suggest that injected hot ions are the major driver of He+ EMIC waves inside the plasmasphere during active time. Expanding plasmasphere during quiet times can provide broad wave source regions for He+ EMIC waves on the dayside. However, H+ EMIC waves outside the plasmasphere show different characteristics, suggesting that these waves are generated by other processes. Jun, C.-W.; Yue, C.; Bortnik, J.; Lyons, L.; Nishimura, Y.; Kletzing, C.; Wygant, J.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2019 YEAR: 2019 DOI: 10.1029/2018JA025886 EMIC waves associated with and without injections; Relationship between EMIC wave activity and energetic H+ flux variation; Simultaneous observations using the Van Allen Probes and GOES satellites; Spatial occurrence distributions of EMIC waves; Van Allen Probes |
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The evolution of the radiation belts in L-shell (L), energy (E), and equatorial pitch-angle (α0) is analyzed during the calm 11-day interval (March 4 \textendashMarch 15) following the March 1 storm 2013. Magnetic Electron and Ion Spectrometer (MagEIS) observations from Van Allen Probes are interpreted alongside 1D and 3D Fokker-Planck simulations combined with consistent event-driven scattering modeling from whistler mode hiss waves. Three (L, E, α0)-regions persist through 11 days of hiss wave scattering; the pitch-angle dependent inner belt core (L~<2.2 and E<700 keV), pitch-angle homogeneous outer belt low-energy core (L>~5 and E~<100 keV), and a distinct pocket of electrons (L~[4.5, 5.5] and E~[0.7, 2] MeV). The pitch-angle homogeneous outer belt is explained by the diffusion coefficients that are roughly constant for α0~<60\textdegree, E>100 keV, 3.5 Ripoll, -F.; Loridan, V.; Denton, M.; Cunningham, G.; Reeves, G.; ik, O.; Fennell, J.; Turner, D.; Drozdov, A; Villa, J.; Shprits, Y; Thaller, S.; Kurth, W.; Kletzing, C.; Henderson, M.; Ukhorskiy, A; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2018 YEAR: 2018 DOI: 10.1029/2018JA026111 electron lifetime; hiss waves; pitch-angle diffusion coefficient; Radiation belts; Van Allen Probes; wave particle interactions |
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Gyroresonant wave-particle interactions with very low frequency whistler mode chorus waves can accelerate subrelativistic seed electrons (hundreds of keV) to relativistic energies in the outer radiation belt during geomagnetic storms. In this study, we conduct a superposed epoch analysis of the chorus wave activity, the seed electron development, and the outer radiation belt electron response between L* = 2.5 and 5.5, for 25 coronal mass ejection and 35 corotating interaction region storms using Van Allen Probes observations. Electron data from the Magnetic Electron Ion Spectrometer and Relativistic Electron Proton Telescope instruments are used to monitor the storm-phase development of the seed and relativistic electrons, and magnetic field measurements from the Electric and Magnetic Field Instrument Suite and Integrated Science instrument are used to identify the chorus wave activity. Our results show a deeper (lower L*), stronger (higher flux), and earlier (epoch time) average seed electron enhancement and a resulting greater average radiation belt electron enhancement in coronal mass ejection storms compared to the corotating interaction region storms despite similar levels and lifetimes of average chorus wave activity for the two storm drivers. The earlier and deeper seed electron enhancement during the coronal mass ejection storms, likely driven by greater convection and substorm activity, provides a higher probability for local acceleration. These results emphasize the importance of the timing and the level of the seed electron enhancements in radiation belt dynamics. Bingham, S.; Mouikis, C.; Kistler, L.; Boyd, A.; Paulson, K.; Farrugia, C.; Huang, C.; Spence, H.; Claudepierre, S.; Kletzing, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2018 YEAR: 2018 DOI: 10.1029/2018JA025963 CIR storms; CME storms; Radiation belts; seed electrons; Van Allen Probes; VLF waves |
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There has been increasing evidence for pitch angle scattering of relativistic electrons by electromagnetic ion cyclotron (EMIC) waves. Theoretical studies have predicted that the loss time scale of MeV electrons by EMIC waves can be very fast, suggesting that MeV electron fluxes rapidly decrease in association with the EMIC wave activity. This study reports on a unique event of MeV electron loss induced by EMIC waves based on Arase, Van Allen Probes, and ground-based network observations. Arase observed a signature of MeV electron loss by EMIC waves, and the satellite and ground-based observations constrained spatial-temporal variations of the EMIC wave activity during the loss event. Multi-satellite observation of MeV electron fluxes showed that ~2.5 MeV electron fluxes substantially decreased within a few tens of minutes where the EMIC waves were present. The present study provides an observational estimate of the loss time scale of MeV electrons by EMIC waves. Kurita, S.; Miyoshi, Y.; Shiokawa, K.; Higashio, N.; Mitani, T.; Takashima, T.; Matsuoka, A.; Shinohara, I.; Kletzing, C.; Blake, J.; Claudepierre, S.; Connors, M.; Oyama, S.; Nagatsuma, T.; Sakaguchi, K.; Baishev, D.; Otsuka, Y.; Published by: Geophysical Research Letters Published on: 11/2018 YEAR: 2018 DOI: 10.1029/2018GL080262 EMIC waves; loss; PWING project; Radiation belt; The Arase satellite; Van Allen Probes |
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Simulations of Van Allen Probes Plasmaspheric Electron Density Observations We simulate equatorial plasmaspheric electron densities using a physics-based model (Cold PLasma, CPL; used in the ring current-atmosphere interactions model) of the source and loss processes of refilling and erosion driven by empirical inputs. The performance of CPL is evaluated against in situ measurements by the Van Allen Probes (Radiation Belt Storm Probes) for two events: the 31 May to 5 June and 15 to 20 January 2013 geomagnetic storms observed in the premidnight and postmidnight magnetic local time (MLT) sectors, respectively. Overall, CPL reproduces the radial extent of the plasmasphere to within a mean absolute difference of urn:x-wiley:jgra:media:jgra54637:jgra54637-math-0001 L. The model electric field responsible for E \texttimes B convection and the parameterization of geomagnetic conditions (under the Kp-index and solar wind properties) implemented by CPL did not account for localized enhancements in the duskward electric field during increased activity. Rather, it was found to be largely dependent on the measure of the quiet time background. This property indicates that the agreement between these simulations and observations does not account for the complete set of physical processes during extreme (strong or weak) geomagnetic conditions impacting the plasmasphere. Nevertheless, at the presented resolution of the model CPL does provide good agreement in reproducing Radiation Belt Storm Probes observations of plasmaspheric density and plasmapause location. De Pascuale, S.; Jordanova, V.; Goldstein, J.; Kletzing, C.; Kurth, W.; Thaller, S.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2018 YEAR: 2018 DOI: 10.1029/2018JA025776 convection; observations; plasmasphere; RBSP; simulation; Van Allen Probes |
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Simultaneous observations of the magnetic field and plasma waves made by the Arase and Van Allen Probe A satellites at different magnetic local time (MLT) enable us to deduce the longitudinal structure of an oxygen torus for the first time. During 04:00\textendash07:10 UT on 24 April 2017, Arase flew from L = 6.2 to 2.0 in the morning sector and detected an enhancement of the average plasma mass up to ~3.5 amu around L = 4.9\textendash5.2 and MLT = 5.0 hr, implying that the plasma consists of approximately 15\% O+ ions. Probe A moved outbound from L = 2.0 to 6.2 in the afternoon sector during 04:10\textendash07:30 UT and observed no clear enhancements in the average plasma mass. For this event, the O+ density enhancement in the inner magnetosphere (i.e., oxygen torus) does not extend over all MLT but is skewed toward the dawn, being described more precisely as a crescent-shaped torus or a pinched torus. e, M.; Matsuoka, A.; Kumamoto, A.; Kasahara, Y.; Goldstein, J.; Teramoto, M.; Tsuchiya, F.; Matsuda, S.; Shoji, M.; Imajo, S.; Oimatsu, S.; Yamamoto, K.; Obana, Y.; Nomura, R.; Fujimoto, A.; Shinohara, I.; Miyoshi, Y.; Kurth, W.; Kletzing, C.; Smith, C.; MacDowall, R.; Published by: Geophysical Research Letters Published on: 10/2018 YEAR: 2018 DOI: 10.1029/2018GL080122 Arase satellite; Geomagnetic storm; inner magnetosphere; oxygen torus; simultaneous observation; Van Allen Probes; Van Allen Probes satellite |
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Inward radial diffusion driven by ULF waves has long been known to be capable of accelerating radiation belt electrons to very high energies within the heart of the belts, but more recent work has shown that radial diffusion values can be highly event-specific and mean values or empirical models may not capture the full significance of radial diffusion to acceleration events. Here we present an event of fast inward radial diffusion, occurring during a period following the geomagnetic storm of 17 March 2015. Ultra-relativistic electrons up to \~8 MeV are accelerated in the absence of intense higher-frequency plasma waves, indicating an acceleration event in the core of the outer belt driven primarily or entirely by ULF wave-driven diffusion. We examine this fast diffusion rate along with derived radial diffusion coefficients using particle and fields instruments on the Van Allen Probes spacecraft mission. Jaynes, A.; Ali, A.; Elkington, S.; Malaspina, D.; Baker, D.; Li, X.; Kanekal, S.; Henderson, M.; Kletzing, C.; Wygant, J.; Published by: Geophysical Research Letters Published on: 09/2018 YEAR: 2018 DOI: 10.1029/2018GL079786 Magnetosphere; radial diffusion; Radiation belts; ULF waves; Van Allen Probes |
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The stimulation of EMIC waves by a magnetospheric compression is perhaps the closest thing to a controlled experiment that is currently possible in magnetospheric physics, in that one prominent factor that can increase wave growth acts at a well-defined time. We present a detailed analysis of EMIC waves observed in the outer dayside magnetosphere by the four Magnetosphere Multiscale (MMS) spacecraft, Van Allen Probe A, and GOES 13, and by four very high latitude ground magnetometer stations in the western hemisphere before, during, and after a modest interplanetary shock on December 14, 2015. Analysis shows several features consistent with current theory, as well as some unexpected features. During the most intense MMS wave burst, which began ~ 1 min after the end of a brief magnetosheath incursion, independent transverse EMIC waves with orthogonal linear polarizations appeared simultaneously at all four spacecraft. He++ band EMIC waves were observed by MMS inside the magnetosphere, whereas almost all previous studies of He++ band EMIC waves observed them only in the magnetosheath and magnetopause boundary layers. Transverse EMIC waves also appeared at Van Allen Probe A and GOES 13 very near the times when the magnetic field compression reached their locations, indicating that the compression lowered the instability threshold to allow for EMIC wave generation throughout the outer dayside magnetosphere. The timing of the EMIC waves at both MMS and Van Allen Probe A was consistent with theoretical expectations for EMIC instabilities based on characteristics of the proton distributions observed by instruments on these spacecraft. Engebretson, M.; Posch, J.; Capman, N.; Campuzano, N.; elik, P.; Allen, R.; Vines, S.; Anderson, B.; Tian, S.; Cattell, C.; Wygant, J.; Fuselier, S.; Argall, M.; Lessard, M.; Torbert, R.; Moldwin, M.; Hartinger, M.; Kim, H.; Russell, C.; Kletzing, C.; Reeves, G.; Singer, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2018 YEAR: 2018 DOI: 10.1029/2018JA025984 |
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Pitch Angle Scattering and Loss of Radiation Belt Electrons in Broadband Electromagnetic Waves A magnetic conjunction between Van Allen Probes spacecraft and the Balloon Array for Radiation-belt Relativistic Electron Losses (BARREL) reveals the simultaneous occurrence of broadband Alfv\ enic fluctuations and multi-timescale modulation of enhanced atmospheric X-ray bremsstrahlung emission. The properties of the Alfv\ enic fluctuations are used to build a model for pitch angle scattering in the outer radiation belt on electron gyro-radii scale field structures. It is shown that this scattering may lead to the transport of electrons into the loss cone over an energy range from hundreds of keV to multi-MeV on diffusive timescales on the order of hours. This process may account for modulation of atmospheric X-ray fluxes observed from balloons and constitute a significant loss process for the radiation belts. Chaston, C.; Bonnell, J.; Halford, A.; Reeves, G.; Baker, D.; Kletzing, C.; Wygant, J.; Published by: Geophysical Research Letters Published on: 09/2018 YEAR: 2018 DOI: 10.1029/2018GL079527 Alfven waves; drift-bounce resonance; energetic particles; Geomagnetic storms; pitch-angle scattering; Radiation belts; Van Allen Probes |
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Determining Plasmaspheric Densities from Observations of Plasmaspheric Hiss A new method of inferring electron plasma densities inside of the plasmasphere is presented. Utilizing observations of the electric and magnetic field wave power associated with plasmaspheric hiss, coupled with the cold plasma dispersion relation, permits calculation of the plasma density. This methodology yields a density estimate for each frequency channel and time interval where plasmaspheric hiss is observed and is shown to yield results that are generally in agreement with densities determined via other methods. A statistical calibration is performed against the density from the upper hybrid line, accounting for both systematic offsets and distribution scatter in the hiss-inferred densities. This calculation and calibration methodology provides accurate density estimates, both statistically and for individual events. These calibrated calculated densities are not subject to the same upper limit as densities inferred via other methodologies, thus permitting density estimates to be extended to lower L shells. This is of particular interest given that fpe/fce ratios indicate favorable conditions for efficient pitch-angle and energy diffusion in this region. Since hiss is almost always observable inside of the plasmasphere, the hiss-inferred densities are available for the majority of time periods, with 79\% data coverage for L < 4. This compares to 33\textendash37\% data coverage for other methods of inferring plasma densities. Due to the high-accuracy of these hiss-inferred densities and their plentiful availability, this methodology provides a viable alternative of calculating event-specific densities, and therefore diffusion coefficients, as opposed to relying on empirical models for periods when densities from other sources are not available. Hartley, D.; Kletzing, C.; De Pascuale, S.; Kurth, W.; ik, O.; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2018 YEAR: 2018 DOI: 10.1029/2018JA025658 Density; EMFISIS; plasmasphere; Plasmaspheric Hiss; Van Allen Probes |
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Determining the wave vector direction of equatorial fast magnetosonic waves We perform polarization analysis of the equatorial fast magnetosonic waves electric field over a 20 minute interval of Van Allen Probes A Waveform Receiver burst mode data. The wave power peaks at harmonics of the proton cyclotron frequency indicating the spacecraft is near or in the source region. The wave vector is inferred from the direction of the major axis of the electric field polarization ellipsoid and the sign of the phase between the longitudinal electric and compressional magnetic field components. We show that wave vector is preferentially in the azimuthal direction as opposed to the radial direction. From Poynting flux analysis one would infer that the wave vector is primarily in the radial direction. We show that the error in the Poynting flux is large ~ 90\textdegree. These results strongly imply that the wave growth occurs during azimuthal propagation in the source region for this event. Boardsen, Scott; Hospodarsky, George; Min, Kyungguk; Averkamp, Terrance; Bounds, Scott; Kletzing, Craig; Pfaff, Robert; Published by: Geophysical Research Letters Published on: 07/2018 YEAR: 2018 DOI: 10.1029/2018GL078695 equatorial fast magnetosonic; E-field polarization analysis; Poynting Flux analysis; Van Allen Probes; wave vector analysis |
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EMIC wave events during the four GEM QARBM challenge intervals This paper presents observations of EMIC waves from multiple data sources during the four GEM challenge events in 2013 selected by the GEM \textquotedblleftQuantitative Assessment of Radiation Belt Modeling\textquotedblright focus group: March 17-18 (Stormtime Enhancement), May 31-June 2 (Stormtime Dropout), September 19-20 (Non-storm Enhancement), and September 23-25 (Non-storm Dropout). Observations include EMIC wave data from the Van Allen Probes, GOES, and THEMIS spacecraft in the near-equatorial magnetosphere and from several arrays of ground-based search coil magnetometers worldwide, as well as localized ring current proton precipitation data from low-altitude POES spacecraft. Each of these data sets provides only limited spatial coverage, but their combination shows consistent occurrence patterns and reveals some events that would not be identified as significant using near-equatorial spacecraft alone. Relativistic and ultrarelativistic electron flux observations, phase space density data, and pitch angle distributions based on data from the REPT and MagEIS instruments on the Van Allen Probes during these events show two cases during which EMIC waves are likely to have played an important role in causing major flux dropouts of ultrarelativistic electrons, particularly near L* ~ 4.0. In three other cases identifiable smaller and more short-lived dropouts appeared, and in five other cases these waves evidently had little or no effect. Engebretson, M.; Posch, J.; Braun, D.; Li, W.; Ma, Q.; Kellerman, A.; Huang, C.-L.; Kanekal, S.; Kletzing, C.; Wygant, J.; Spence, H.; Baker, D.; Fennell, J.; Angelopoulos, V.; Singer, H.; Lessard, M.; Horne, R.; Raita, T.; Shiokawa, K.; Rakhmatulin, R.; Dmitriev, E.; Ermakova, E.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2018 YEAR: 2018 DOI: 10.1029/2018JA025505 |
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We use the measurements performed by the DEMETER (2004-2010) and the Van Allen Probes (2012-2016, still operating) spacecraft to investigate the longitudinal dependence of the intensity of whistler mode waves in the Earth\textquoterights inner magnetosphere. We show that a significant longitudinal dependence is observed inside the plasmasphere on the nightside, primarily in the frequency range 400 Hz\textendash2 kHz. On the other hand, almost no longitudinal dependence is observed on the dayside. The obtained results are compared to the lightning occurrence rate provided by the OTD/LIS mission normalized by a factor accounting for the ionospheric attenuation. The agreement between the two dependencies indicates that lightning generated electromagnetic waves may be responsible for the observed effect, thus substantially affecting the overall wave intensity in the given frequency range. Finally, we show that the longitudinal dependence is most pronounced for waves with oblique wave normal angles. ahlava, J.; emec, F.; ik, O.; a, I.; Hospodarskyy, G.; Parrot, M.; Kurth, W.; Bortnik, J.; Kletzing, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2018 YEAR: 2018 DOI: 10.1029/2018JA025284 |
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Magnetospheric plasma waves play a significant role in ring current and radiation belt dynamics, leading to pitch angle scattering loss and/or stochastic acceleration of the particles. During a non-storm time dropout event on 24 September 2013, intense electromagnetic ion cyclotron (EMIC) waves were detected by Van Allen Probe A (Radiation Belt Storm Probes-A). We quantitatively analyze a conjunction event when Van Allen Probe A was located approximately along the same magnetic field line as MetOp-01, which detected simultaneous precipitation of >30 keV protons and energetic electrons over an unexpectedly broad energy range (>~30 keV). Multipoint observations together with quasi-linear theory provide direct evidence that the observed electron precipitation at higher energy (>~700 keV) is primarily driven by EMIC waves. However, the newly observed feature of the simultaneous electron precipitation extending down to ~30 keV is not supported by existing theories and raises an interesting question on whether EMIC waves can scatter such low-energy electrons. Capannolo, L.; Li, W.; Ma, Q.; Zhang, X.-J.; Redmon, R.; Rodriguez, J.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Engebretson, M.; Spence, H.; Reeves, G.; Published by: Geophysical Research Letters Published on: 07/2018 YEAR: 2018 DOI: 10.1029/2018GL078604 EMIC waves; energetic particle precipitation; pitch angle scattering; Radiation belts; Van Allen Probes; wave particle interactions |
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By analyzing observations from Van Allen Probes in its inbound and outbound orbits, we present evidence of coherent enhancement of cold plasmaspheric electrons and ions due to drift-bounce resonance with ULF waves. From 18:00 UT on 28 May 2017 to 10:00 UT on 29 May 2017, newly formed poloidal mode standing ULF waves with significant electric field oscillations were observed in two consecutive orbits when Probe B was travelling inbound. In contrast to observations during outbound orbits, the cold (< 150 eV) electorns measured by the HOPE instrument were characterized by flux enhancements several times larger and bi-directional pitch angle distributions during inbound orbits. The electron number density inferred from upper hybrid waves is twice as larger as during inbound orbits, which were also confirmed by an increase of spacecraft potential. The observed ULF waves are identified as second harmonic modes that satisfy the drift-bounce resonant condition of N=1 with cold electrons. An enhancement of the plasmaspheric ion number density to restore charge neutrality of plasmas in inbound orbits is observed, which is associated with an increase of ULF wave periods. The observations suggest that the dynamics of plasmaspheric electrons is modified by ULF waves through drift-bounce resonance, and that plasmaspheric ions are indirectly impacted. Ren, Jie; Zong, Qiu-Gang; Miyoshi, Yoshizumi; Rankin, Robert; Spence, Harlan; Funsten, Herbert; Wygant, John; Kletzing, Craig; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2018 YEAR: 2018 DOI: 10.1029/2018JA025255 Cold plasmaspheric electrons acceleration; Drfit-bounce resonance; Modification of electron and ion density profile; Substorm activities; ULF waves; Van Allen Probes |
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Resonant interactions between electrons and chorus waves are responsible for a wide range of phenomena in near-Earth space (e.g., diffuse aurora, acceleration of MeV electrons, etc.). Although quasi-linear diffusion is believed to be the primary paradigm for describing such interactions, an increasing number of investigations suggest that nonlinear effects are also important in controlling the rapid dynamics of electrons. However, present models of nonlinear wave-particle interactions, which have been successfully used to describe individual short-term events, are not directly applicable for a statistical evaluation of nonlinear effects and the long-term dynamics of the outer radiation belt, because they lack information on the properties of intense (nonlinearly resonating with electrons) chorus waves. In this paper, we use the THEMIS and Van Allen Probes datasets of field-aligned chorus waveforms to study two key characteristics of these waves: effective amplitude w (nonlinear interaction can occur when w > 2) and wave-packet length β (the number of wave periods within it). While as many as 10 - 15\% of chorus wave-packets are sufficiently intense (w > 2 - 3) to interact nonlinearly with relativistic electrons, most of them are short (β < 10) reducing the efficacy of such interactions. Revised models of non-linear interactions are thus needed to account for the long-term effects of these common, intense but short chorus wave packets. We also discuss the dependence of w, β on location (MLT, L-shell) and on the properties of the suprathermal electron population. Zhang, X.-J.; Thorne, R.; Artemyev, A.; Mourenas, D.; Angelopoulos, V.; Bortnik, J.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2018 YEAR: 2018 DOI: 10.1029/2018JA025390 chorus waves; Effective amplitude; nonlinear wave-particle interaction; spatial distribution; statistics; Van Allen Probes; Wave-packet length |
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Response of Different Ion Species to Local Magnetic Dipolarization Inside Geosynchronous Orbit This paper examines how hydrogen, helium and oxygen (H, He and O) ion fluxes at 1\textendash1000 keV typically respond to local magnetic dipolarization inside geosynchronous orbit (GEO). We extracted 144 dipolarizations which occurred at magnetic inclination > 30\textdegree from the 2012\textendash2016 tail seasons\textquoteright observations of the Van Allen Probes spacecraft and then defined typical flux changes of these ion species by performing a superposed epoch analysis. On average, the dipolarization inside GEO is accompanied by a precursory transient decrease in the northward magnetic field component, transient impulsive enhancement in the westward electric field component, and decrease (increase) in the proton density (temperature). The coincident ion species experience an energy-dependent flux change, consisting of enhancement (depression) at energies above (below) ~50 keV. These properties morphologically resemble those around dipolarization fronts (or fast flows) in the near-Earth tail. A distinction among the ion species is the average energy of the flux ratio peak, being at 200\textendash400 keV (100\textendash200 keV) for He (H and O) ions. The flux ratio peaks at different energies likely reflect the different charge states of injected ionospheric- and/or solar wind-origin ion species. The ion spectra become harder for sharp dipolarizations, suggesting the importance of accompanying electric field in transporting and/or energizing the ions efficiently. Interestingly, the average flux ratio peak does not differ significantly among the ion species for ~2 min after onset, which implies that mass-dependent acceleration process is less important in the initial stage of dipolarization. Motoba, T.; Ohtani, S.; Gkioulidou, M.; Ukhorskiy, A.; Mitchell, D.; Takahashi, K.; Lanzerotti, L.; Kletzing, C.; Spence, H.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2018 YEAR: 2018 DOI: 10.1029/2018JA025557 deep inside geosynchronous orbit; dipolarizations; Ion injections; ion species; Van Allen Probes |
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The transport mechanism of the ring current ions differs among ion energies. Lower-energy (≲150 keV) ions are well known to be transported convectively. Higher-energy (≳150 keV) protons are reported to be transported diffusively, while there are few reports about transport of higher-energy oxygen ions. We report the radial transport of higher-energy oxygen ions into the deep inner magnetosphere during the late main phase of the magnetic storm on 23\textendash25 April 2013 observed by the Van Allen Probes spacecraft. An enhancement of 1\textendash100 mHz magnetic fluctuations is simultaneously observed. Observations of 3 and 30 mHz geomagnetic pulsations indicate the azimuthal mode number is <=10. The fluctuations can resonate with the drift and bounce motions of the oxygen ions. The results suggest that the combination of the drift and drift-bounce resonances is responsible for the radial transport of higher-energy oxygen ions. Mitani, K.; Seki, K.; Keika, K.; Gkioulidou, M.; Lanzerotti, L.; Mitchell, D.; Kletzing, C.; Published by: Geophysical Research Letters Published on: 05/2018 YEAR: 2018 DOI: 10.1029/2018GL077500 |
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Generation process of large-amplitude upper band chorus emissions observed by Van Allen Probes We analyze large-amplitude upper-band chorus emissions measured near the magnetic equator by the EMFISIS (Electric and Magnetic Field Instrument Suite and Integrated Science) instrument package onboard the Van Allen Probes. In setting up the parameters of source electrons exciting the emissions based on theoretical analyses and observational results measured by the HOPE (Helium Oxygen Proton Electron) instrument, we calculate threshold and optimum amplitudes with the nonlinear wave growth theory. We find that the optimum amplitude is larger than the threshold amplitude obtained in the frequency range of the chorus emissions and that the wave amplitudes grow between the threshold and optimum amplitudes. In the frame of the wave growth process, the nonlinear growth rates are much greater than the linear growth rates. Kubota, Yuko; Omura, Yoshiharu; Kletzing, Craig; Reeves, Geoff; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2018 YEAR: 2018 DOI: 10.1029/2017JA024782 Chorus; energetic electrons; nonlinear wave-particle interaction; observation; Radiation belt; Van Allen Probes |
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A poloidal Pc4 wave and proton flux oscillations are observed in the inner magnetosphere on the dayside near the magnetic equator by the Van Allen Probes spacecraft on 2 March 2014. The flux oscillations are observed in the energy range of 67.0 keV to 268.8 keV with the same frequency of the poloidal Pc4 wave. We find pitch angle and energy dispersion in the phase difference between the poloidal magnetic field and the proton flux oscillations, which are features of drift-bounce resonance. We estimate the resonance energy to be ~120 keV for pitch angle (α) of 30\textdegree or 150\textdegree, and 170\textendash180 keV for α = 50\textdegree or 130\textdegree. To examine the direction of energy flow between protons and the wave, we calculate the sign of the gradient of proton phase space density (df/dW) on both the inbound and outbound legs of the orbit. We find the gradient to be outward on both legs, which means that energy is transferred from the protons to the wave. During the poloidal Pc4 wave event, the Dst* index shows a measurable increase of ~6.7 nT. We estimate the total energy loss of the ring current from the recovery of the Dst* index and from the variation of proton flux by the drift-bounce resonance. We suggest that energy transfer from the ring current protons to the poloidal Pc4 wave via the drift-bounce resonance contributes to up to ~85 \% of the increase of the Dst* index. Oimatsu, S.; e, M.; Takahashi, K.; Yamamoto, K.; Keika, K.; Kletzing, C.; Smith, C.; MacDowall, R.; Mitchell, D.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2018 YEAR: 2018 DOI: 10.1029/2017JA025087 |