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Found 21 results
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2019
Authors: Yu J., Li L. Y., Cui J., Cao J. B., and Wang J.
Title: Effect of Low‐Harmonic Magnetosonic Waves on the Radiation Belt Electrons Inside the Plasmasphere
Abstract: In this paper, we presented two observational cases and simulations to indicate the relationship between the formation of butterfly‐like electron pitch angle distributions and the emission of low‐harmonic (LH) fast magnetosonic (MS) waves inside the high‐density plasmasphere. In the wave emission region, the pitch angle of relativistic (>1 MeV) electrons becomes obvious butterfly‐like distributions for both events (near‐equatorially mirroring electrons are transported to lower pitch angles). Unlike relativistic (>1 MeV) electrons, energetic electrons (<1 MeV) change slightly, except that relatively low‐energy electrons (<~150 keV) show butterfly‐like distributions in the 21 August 2013 event. In theory, the LH MS waves can affect different‐energy electrons through the bounc. . .
Date: 05/2019 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA026328 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA026328
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Authors: Zhu Hui, Chen Lunjin, Liu Xu, and Shprits Yuri Y
Title: Modulation of Locally Generated Equatorial Noise by ULF Wave
Abstract: In this paper we report a rare and fortunate event of fast magnetosonic (MS, also called equatorial noise) waves modulated by compressional ultralow frequency (ULF) waves measured by Van Allen Probes. The characteristics of MS waves, ULF waves, proton distribution, and their potential correlations are analyzed. The results show that ULF waves can modulate the energetic ring proton distribution and in turn modulate the MS generation. Furthermore, the variation of MS intensities is attributed to not only ULF wave activities but also the variation of background parameters, for example, number density. The results confirm the opinion that MS waves are generated by proton ring distribution and propose a new modulation phenomenon.
Date: 04/2019 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA026199 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA026199
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2018
Authors: Yuan Zhigang, Yu Xiongdong, Huang Shiyong, Qiao Zheng, Yao Fei, et al.
Title: Cold Ion Heating by Magnetosonic Waves in a Density Cavity of the Plasmasphere
Abstract: Fast magnetosonic (MS) waves play an important role in the dynamics of the inner magnetosphere. Theoretical prediction and simulation have demonstrated that MS waves can heat cold ions. However, direct observational evidence of cold ion heating by MS waves has so far remained elusive. In this paper, we show a typical event of cold ion heating by magnetosonic waves in a density cavity of the plasmasphere with observations of the Van Allen Probe mission on 22 August 2013. During enhancements of the MS wave intensity in the density cavity, the fluxes of trapped H+ and He+ ions with energies of 10–100 eV were observed to increase, implying that cold plasmaspheric ions were heated through high-order resonances with the MS waves. Based on simultaneous observations of ring current protons, we h. . .
Date: 02/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2017JA024919 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017JA024919/full
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Authors: Hua Man, Ni Binbin, Fu Song, Gu Xudong, Xiang Zheng, et al.
Title: Combined Scattering of Outer Radiation Belt Electrons by Simultaneously Occurring Chorus, Exohiss, and Magnetosonic Waves
Abstract: We report a typical event that fast magnetosonic (MS) waves, exohiss, and two‐band chorus waves occurred simultaneously on the dayside observed by Van Allen Probes on 25 December 2013. By combining calculations of electron diffusion coefficients and 2‐D Fokker‐Planck diffusion simulations, we quantitatively analyze the combined scattering effect of multiple waves to demonstrate that the net impact of combined scattering does not simply depend on the wave intensity dominance of various plasma waves. Although the observed MS waves are most intense, the electron butterfly distribution is inhibited by exohiss and chorus, and electrons are considerably accelerated by combined scattering of MS and chorus waves. The simulated electron pitch angle distributions exhibit the variation trend co. . .
Date: 09/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL079533 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL079533
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Authors: Liu Bin, Li Liuyuan, Yu Jiang, and Cao Jinbin
Title: The Effect of Hot Protons on Magnetosonic Waves Inside and Outside the Plasmapause: New Observations and Theoretic Results
Abstract: Based on the wave and proton observations by Van Allen Probes A and B, we examined the effects of hot protons (0.01–50 keV) on fast magnetosonic (MS) waves inside and outside the Earth's plasmasphere. In the low-density plasma trough outside the plasmapause, the gyroresonance interactions between hot protons and MS waves not only cause the MS wave growth at some frequencies but also lead to the damping of MS waves at other frequencies, which depends on the proton phase space density gradient and the ambient plasma density. The gyroresonance of the observed hot protons cannot excite MS waves near the lower hybrid resonance frequency and even causes the MS wave damping. Thus, the frequencies of the observed MS waves outside the plasmapause are usually lower than the lower hybrid resonance . . .
Date: 01/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2017JA024676 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017JA024676/full
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Authors: Liu Nigang, Su Zhenpeng, Zheng Huinan, Wang Yuming, and Wang Shui
Title: Prompt Disappearance and Emergence of Radiation Belt Magnetosonic Waves Induced by Solar Wind Dynamic Pressure Variations
Abstract: Magnetosonic waves are highly oblique whistler mode emissions transferring energy from the ring current protons to the radiation belt electrons in the inner magnetosphere. Here we present the first report of prompt disappearance and emergence of magnetosonic waves induced by the solar wind dynamic pressure variations. The solar wind dynamic pressure reduction caused the magnetosphere expansion, adiabatically decelerated the ring current protons for the Bernstein mode instability, and produced the prompt disappearance of magnetosonic waves. On the contrary, because of the adiabatic acceleration of the ring current protons by the solar wind dynamic pressure enhancement, magnetosonic waves emerged suddenly. In the absence of impulsive injections of hot protons, magnetosonic waves were observa. . .
Date: 01/2018 Publisher: Geophysical Research Letters DOI: 10.1002/2017GL076382 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017GL076382/full
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2017
Authors: Su Zhenpeng, Wang Geng, Liu Nigang, Zheng Huinan, Wang Yuming, et al.
Title: Direct observation of generation and propagation of magnetosonic waves following substorm injection
Abstract: Magnetosonic whistler mode waves play an important role in the radiation belt electron dynamics. Previous theory has suggested that these waves are excited by the ring distributions of hot protons and can propagate radially and azimuthally over a broad spatial range. However, because of the challenging requirements on satellite locations and data-processing techniques, this theory was difficult to validate directly. Here we present some experimental tests of the theory on the basis of Van Allen Probes observations of magnetosonic waves following substorm injections. At higher L-shells with significant substorm injections, the discrete magnetosonic emission lines started approximately at the proton gyrofrequency harmonics, qualitatively consistent with the prediction of linear proton Bernst. . .
Date: 07/2018 Publisher: Geophysical Research Letters DOI: 10.1002/2017GL074362 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017GL074362/full
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Authors: Yuan Zhigang, Yu Xiongdong, Huang Shiyong, Wang Dedong, and Funsten Herbert O.
Title: In situ observations of magnetosonic waves modulated by background plasma density
Abstract: We report in situ observations by the Van Allen Probe mission that magnetosonic (MS) waves are clearly relevant to appear relevant to the background plasma number density. As the satellite moved across dense and tenuous plasma alternatively, MS waves occurred only in lower density region. As the observed protons with ‘ring’ distributions provide free energy, local linear growth rates are calculated and show that magnetosonic waves can be locally excited in tenuous plasma. With variations of the background plasma density, the temporal variations of local wave growth rates calculated with the observed proton ring distributions, show a remarkable agreement with those of the observed wave amplitude. Therefore, the paper provides a direct proof that background plasma densities can modulate . . .
Date: 07/2017 Publisher: Geophysical Research Letters DOI: 10.1002/2017GL074681 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017GL074681/full
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Authors: Li L. Y., Yu J., Cao J. B., Yang J. Y., Li X, et al.
Title: Roles of whistler-mode waves and magnetosonic waves in changing the outer radiation belt and the slot region
Abstract: Using the Van Allen Probe long-term (2013 – 2015) observations and quasi-linear simulations of wave-particle interactions, we examine the combined or competing effects of whistler-mode waves (chorus or hiss) and magnetosonic (MS) waves on energetic (<0.5 MeV) and relativistic (>0.5 MeV) electrons inside and outside the plasmasphere. Although whistler-mode chorus waves and MS waves can singly or jointly accelerate electrons from the hundreds of keV energy to the MeV energy in the low-density trough, most of the relativistic electron enhancement events are best correlated with the chorus wave emissions outside the plasmapause. Inside the plasmasphere, intense plasmaspheric hiss can cause the net loss of relativistic electrons via persistent pitch angle scattering, regardless of whether. . .
Date: 04/2017 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA023634 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016JA023634/full
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2016
Authors: Li Jinxing, Ni Binbin, Ma Qianli, Xie Lun, Pu Zuyin, et al.
Title: Formation of Energetic Electron Butterfly Distributions by Magnetosonic Waves via Landau Resonance
Abstract: Radiation belt electrons can exhibit different types of pitch angle distributions in response to various magnetospheric processes. Butterfly distributions, characterized by flux minima at pitch angles around 90°, are broadly observed in both the outer and inner belts and the slot region. Butterfly distributions close to the outer magnetospheric boundary have been attributed to drift shell splitting and losses to the magnetopause. However, their occurrence in the inner belt and the slot region has hitherto not been resolved. By analyzing the particle and wave data collected by the Van Allen Probes during a geomagnetic storm, we combine test particle calculations and Fokker-Planck simulations to reveal that scattering by equatorial magnetosonic waves is a significant cause for the formation. . .
Date: 04/2016 Publisher: Geophysical Research Letters Pages: n/a - n/a DOI: 10.1002/2016GL067853 Available at: http://doi.wiley.com/10.1002/2016GL067853http://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2F2016GL067853
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Authors: Li Jinxing, Bortnik Jacob, Thorne Richard M, Li Wen, Ma Qianli, et al.
Title: Ultrarelativistic electron butterfly distributions created by parallel acceleration due to magnetosonic waves
Abstract: The Van Allen Probe observations during the recovery phase of a large storm that occurred on 17 March 2015 showed that the ultrarelativistic electrons at the inner boundary of the outer radiation belt (L* = 2.6–3.7) exhibited butterfly pitch angle distributions, while the inner belt and the slot region also showed evidence of sub-MeV electron butterfly distributions. Strong magnetosonic waves were observed in the same regions and at the same time periods as these butterfly distributions. Moreover, when these magnetosonic waves extended to higher altitudes (L* = 4.1), the butterfly distributions also extended to the same region. Combining test particle calculations and Fokker-Planck diffusion simulations, we successfully reproduced the formation of the ultrarelativistic electron b. . .
Date: 04/2016 Publisher: Journal of Geophysical Research: Space Physics Pages: 3212 - 3222 DOI: 10.1002/2016JA022370 Available at: http://doi.wiley.com/10.1002/2016JA022370
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2015
Authors: Ma Qianli, Li Wen, Thorne Richard M, Bortnik Jacob, Kletzing C A, et al.
Title: Electron scattering by magnetosonic waves in the inner magnetosphere
Abstract: We investigate the importance of electron scattering by magnetosonic waves in the Earth's inner magnetosphere. A statistical survey of the magnetosonic wave amplitude and wave frequency spectrum, as a function of geomagnetic activity, is performed using the Van Allen Probes wave measurements, and is found to be generally consistent with the wave distribution obtained from previous spacecraft missions. Outside the plasmapause the statistical frequency distribution of magnetosonic waves follows the variation of the lower hybrid resonance frequency, but this trend is not observed inside the plasmasphere. Drift and bounce averaged electron diffusion rates due to magnetosonic waves are calculated using a recently developed analytical formula. The resulting time scale of electron energization du. . .
Date: 12/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA021992 Available at: http://doi.wiley.com/10.1002/2015JA021992http://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2F2015JA021992
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Authors: Němec F., Santolik O, Hrbáčková Z., Pickett J. S., and Cornilleau-Wehrlin N.
Title: Equatorial noise emissions with quasiperiodic modulation of wave intensity
Abstract: Equatorial noise (EN) emissions are electromagnetic wave events at frequencies between the proton cyclotron frequency and the lower hybrid frequency observed in the equatorial region of the inner magnetosphere. They propagate nearly perpendicular to the ambient magnetic field, and they exhibit a harmonic line structure characteristic of the proton cyclotron frequency in the source region. However, they were generally believed to be continuous in time. We investigate more than 2000 EN events observed by the Spatio-Temporal Analysis of Field Fluctuations and Wide-Band Data Plasma Wave investigation instruments on board the Cluster spacecraft, and we show that this is not always the case. A clear quasiperiodic (QP) time modulation of the wave intensity is present in more than 5% of events. We. . .
Date: 04/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020816 Available at: http://doi.wiley.com/10.1002/2014JA020816
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Authors: Němec F., Santolik O, Hrbáčková Z., and Cornilleau-Wehrlin N.
Title: Intensities and spatiotemporal variability of equatorial noise emissions observed by the Cluster spacecraft
Abstract: Equatorial noise (EN) emissions are electromagnetic waves observed in the equatorial region of the inner magnetosphere at frequencies between the proton cyclotron frequency and the lower hybrid frequency. We present the analysis of 2229 EN events identified in the Spatio-Temporal Analysis of Field Fluctuations (STAFF) experiment data of the Cluster spacecraft during the years 2001–2010. EN emissions are distinguished using the polarization analysis, and their intensity is determined based on the evaluation of the Poynting flux rather than on the evaluation of only the electric/magnetic field intensity. The intensity of EN events is analyzed as a function of the frequency, the position of the spacecraft inside/outside the plasmasphere, magnetic local time, and the geomagnetic activity. Th. . .
Date: 03/2015 Publisher: Journal of Geophysical Research: Space Physics Pages: 1620 - 1632 DOI: 10.1002/2014JA020814 Available at: http://doi.wiley.com/10.1002/2014JA020814
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Authors: Posch J. L, Engebretson M. J., Olson C. N., Thaller S. A., Breneman A. W., et al.
Title: Low-harmonic magnetosonic waves observed by the Van Allen Probes
Abstract: Purely compressional electromagnetic waves (fast magnetosonic waves), generated at multiple harmonics of the local proton gyrofrequency, have been observed by various types of satellite instruments (fluxgate and search coil magnetometers and electric field sensors), but most recent studies have used data from search coil sensors, and many have been restricted to high harmonics. We report here on a survey of low-harmonic waves, based on electric and magnetic field data from the EFW double probe and EMFISIS fluxgate magnetometer instruments, respectively, on the Van Allen Probes spacecraft during its first full precession through all local times, from October 1, 2012 through July 13, 2014. These waves were observed both inside and outside the plasmapause (PP), at L shells from 2.4 to ~6 (the. . .
Date: 07/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA021179 Available at: http://doi.wiley.com/10.1002/2015JA021179
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Authors: Chen Lunjin, Maldonado Armando, Bortnik Jacob, Thorne Richard M, Li Jinxing, et al.
Title: Nonlinear Bounce Resonances between Magnetosonic Waves and Equatorially Mirroring Electrons
Abstract: Equatorially mirroring energetic electrons pose an interesting scientific problem, since they generally cannot resonate with any known plasma waves and hence cannot be scattered down to lower pitch angles. Observationally it is well known that the fluxof these equatorial particles does not simply continue to build up indefinitely, and so a mechanism must necessarily exist that transports these particles from a equatorial pitch angle of 90 degrees down to lower values. However this mechanism has not been uniquely identified yet. Here, we investigate the mechanism of bounce resonance with equatorial noise (or fast magnetosonic waves). A test particle simulation is used to examine the effects of monochromatic magnetosonic waves on the equatorially mirroring energetic electrons, with a special. . .
Date: 06/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA021174 Available at: http://doi.wiley.com/10.1002/2015JA021174
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Authors: Xiao Fuliang, Zhou Qinghua, He Yihua, Yang Chang, Liu Si, et al.
Title: Penetration of magnetosonic waves into the plasmasphere observed by the Van Allen Probes
Abstract: During the small storm on 14–15 April 2014, Van Allen Probe A measured a continuously distinct proton ring distribution and enhanced magnetosonic (MS) waves along its orbit outside the plasmapause. Inside the plasmasphere, strong MS waves were still present but the distinct proton ring distribution was falling steeply with distance. We adopt a sum of subtracted bi-Maxwellian components to model the observed proton ring distribution and simulate the wave trajectory and growth. MS waves at first propagate toward lower L shells outside the plasmasphere, with rapidly increasing path gains related to the continuous proton ring distribution. The waves then gradually cross the plasmapause into the deep plasmasphere, with almost unchanged path gains due to the falling proton ring distribution an. . .
Date: 09/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2015GL065745 Available at: http://onlinelibrary.wiley.com/wol1/doi/10.1002/2015GL065745/full
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Authors: Hrbáčková Z., Santolik O, Němec F., Macúšová E., and Cornilleau-Wehrlin N.
Title: Systematic analysis of occurrence of equatorial noise emissions using 10 years of data from the Cluster mission
Abstract: We report results of a systematic analysis of equatorial noise (EN) emissions which are also known as fast magnetosonic waves. EN occurs in the vicinity of the geomagnetic equator at frequencies between the local proton cyclotron frequency and the lower hybrid frequency. Our analysis is based on the data collected by the Spatio-Temporal Analysis of Field Fluctuations–Spectrum Analyzer instruments on board the four Cluster spacecraft. The data set covers the period from January 2001 to December 2010. We have developed selection criteria for the visual identification of these emissions, and we have compiled a list of more than 2000 events identified during the analyzed time period. The evolution of the Cluster orbit enables us to investigate a large range of McIlwain's parameter from about. . .
Date: 02/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020268 Available at: http://doi.wiley.com/10.1002/2014JA020268
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2014
Authors: Ma Qianli, Li Wen, Chen Lunjin, Thorne Richard M, and Angelopoulos Vassilis
Title: Magnetosonic wave excitation by ion ring distributions in the Earth's inner magnetosphere
Abstract: Combining Time History of Events and Macroscale Interaction during Substorms (THEMIS) wave and particle observations and a quantitative calculation of linear wave growth rate, we demonstrate that magnetosonic (MS) waves can be locally excited by ion ring distributions in the Earth's magnetosphere when the ion ring energy is comparable to the local Alfven energy. MS waves in association with ion ring distributions were observed by THEMIS A on 24 November 2010 in the afternoon sector, both outside the plasmapause where the wave spectrum varied with fLHR and inside the plasmapause where the wave frequency band remained nearly constant. Our plasma instability analysis in three different regions shows that higher and narrow frequency band MS waves are excited locally outside the plasmapause, an. . .
Date: 02/2014 Publisher: Journal of Geophysical Research: Space Physics Pages: 844 - 852 DOI: 10.1002/2013JA019591 Available at: http://doi.wiley.com/10.1002/2013JA019591
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Authors: Ma Q, Li W, Chen L, Thorne R M, Kletzing C A, et al.
Title: The trapping of equatorial magnetosonic waves in the Earth's outer plasmasphere
Abstract: We investigate the excitation and propagation of equatorial magnetosonic waves observed by the Van Allen Probes and describe evidence for a trapping mechanism for magnetosonic waves in the Earth's plasmasphere. Intense equatorial magnetosonic waves were observed inside the plasmasphere in association with a pronounced proton ring distribution, which provides free energy for wave excitation. Instability analysis along the inbound orbit demonstrates that broadband magnetosonic waves can be excited over a localized spatial region near the plasmapause. The waves can subsequently propagate into the inner plasmasphere and remain trapped over a limited radial extent, consistent with the predictions of near-perpendicular propagation. By performing a similar analysis on another observed magnetosoni. . .
Date: 09/2014 Publisher: Geophysical Research Letters Pages: 6307 - 6313 DOI: 10.1002/2014GL061414 Available at: http://doi.wiley.com/10.1002/2014GL061414
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Authors: Betz Eric O.
Title: Trapping waves in Earth's plasmasphere
Abstract: Earth's magnetic field traps donut-shaped bands of radiation in a belt around the planet that react to solar eruptions by growing and shrinking. The Van Allen belts consist of two rings filled with particles from the solar wind and cosmic rays. Within the outer ring of the Van Allen belt sits the plasmasphere, which is the innermost part of the planet's magnetic field and home to low-energy charged particles.
Date: 12/2014 Publisher: Eos, Transactions American Geophysical Union Pages: 472 - 472 DOI: 10.1002/2014EO490016 Available at: http://doi.wiley.com/10.1002/eost.v95.49http://doi.wiley.com/10.1002/2014EO490016
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