Biblio

Found 11 results
Filters: Keyword is magnetic storm  [Clear All Filters]
2018
Authors: Mitani K., Seki K., Keika K, Gkioulidou M., Lanzerotti L J, et al.
Title: Radial Transport of Higher-Energy Oxygen Ions Into the Deep Inner Magnetosphere Observed by Van Allen Probes
Abstract: 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 23–25 April 2013 observed by the Van Allen Probes spacecraft. An enhancement of 1–100 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 s. . .
Date: 05/2018 Publisher: Geophysical Research Letters DOI: 10.1029/2018GL077500 Available at: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GL077500
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Authors: Xiong Ying, Xie Lun, Chen Lunjin, Ni Binbin, Fu Suiyan, et al.
Title: The Response of the Energy Content of the Outer Electron Radiation Belt to Geomagnetic Storms
Abstract: Using the data from the Van Allen Probe‐A spacecraft, the variability of the total outer radiation belt (2.5300 keV) is investigated for the first time during 51 isolated storms spanning from October 2012 to May 2017. The statistical results show that the TRBEEC exhibits no‐change in 20% of the storms and gets enhanced during 80% of them. The sub‐relativistic electrons (300‐500 keV) and relativistic electrons (0.5‐2.0 MeV) equally contribute to the TRBEEC during the main phases, while in the recovery phases, the relativistic electrons contribute up to 80% of the TRBEEC. The results of the superposed epoch analysis of the solar wind parameters and geomagnetic indices indicate that the TRBEEC enhancement events prefe. . .
Date: 09/2018 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2018JA025475 Available at: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JA025475
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2017
Authors: Le G., Chi P. J., Strangeway R J, Russell C. T., Slavin J. A., et al.
Title: Global observations of magnetospheric high- m poloidal waves during the 22 June 2015 magnetic storm
Abstract: We report global observations of high-m poloidal waves during the recovery phase of the 22 June 2015 magnetic storm from a constellation of widely spaced satellites of five missions including Magnetospheric Multiscale (MMS), Van Allen Probes, Time History of Events and Macroscale Interactions during Substorm (THEMIS), Cluster, and Geostationary Operational Environmental Satellites (GOES). The combined observations demonstrate the global spatial extent of storm time poloidal waves. MMS observations confirm high azimuthal wave numbers (m ~ 100). Mode identification indicates the waves are associated with the second harmonic of field line resonances. The wave frequencies exhibit a decreasing trend as L increases, distinguishing them from the single-frequency global poloidal modes normally obs. . .
Date: 04/2017 Publisher: Geophysical Research Letters DOI: 10.1002/2017GL073048 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2017GL073048/full
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2016
Authors: Liu Jiang, Angelopoulos V, Zhang Xiao-Jia, Turner D. L., Gabrielse C., et al.
Title: Dipolarizing flux bundles in the cis-geosynchronous magnetosphere: relationship between electric fields and energetic particle injections
Abstract: Dipolarizing flux bundles (DFBs) are small flux tubes (typically < 3 RE in XGSM and YGSM) in the nightside magnetosphere that have magnetic field more dipolar than the background. Although DFBs are known to accelerate particles, creating energetic particle injections outside geosynchronous orbit (trans-GEO), the nature of the acceleration mechanism and the importance of DFBs in generating injections inside geosynchronous orbit (cis-GEO) are unclear. Our statistical study of cis-GEO DFBs using data from the Van Allen Probes reveals that just like trans-GEO DFBs, cis-GEO DFBs occur most often in the pre-midnight sector, but their occurrence rate is ~1/3 that of trans-GEO DFBs. Half the cis-GEO DFBs are accompanied by an energetic particle injection and have an electric field three times stro. . .
Date: 01/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA021691 Available at: http://doi.wiley.com/10.1002/2015JA021691
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Authors: Zhang X.-J., Li W, Thorne R M, Angelopoulos V, Ma Q, et al.
Title: Physical mechanism causing rapid changes in ultrarelativistic electron pitch angle distributions right after a shock arrival: Evaluation of an electron dropout event
Abstract: Three mechanisms have been proposed to explain relativistic electron flux depletions (dropouts) in the Earth's outer radiation belt during storm times: adiabatic expansion of electron drift shells due to a decrease in magnetic field strength, magnetopause shadowing and subsequent outward radial diffusion, and precipitation into the atmosphere (driven by EMIC wave scattering). Which mechanism predominates in causing electron dropouts commonly observed in the outer radiation belt is still debatable. In the present study, we evaluate the physical mechanism that may be primarily responsible for causing the sudden change in relativistic electron pitch angle distributions during a dropout event observed by Van Allen Probes during the main phase of the 27 February 2014 storm. During this event, t. . .
Date: 09/2016 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA022517 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016JA022517/abstract
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Authors: Zhang X.-J., Li W, Thorne R M, Angelopoulos V, Bortnik J, et al.
Title: Statistical distribution of EMIC wave spectra: Observations from Van Allen Probes
Abstract: It has been known that electromagnetic ion cyclotron (EMIC) waves can precipitate ultrarelativistic electrons through cyclotron resonant scattering. However, the overall effectiveness of this mechanism has yet to be quantified, because it is difficult to obtain the global distribution of EMIC waves that usually exhibit limited spatial presence. We construct a statistical distribution of EMIC wave frequency spectra and their intensities based on Van Allen Probes measurements from September 2012 to December 2015. Our results show that as the ratio of plasma frequency over electron gyrofrequency increases, EMIC wave power becomes progressively dominated by the helium band. There is a pronounced dawn-dusk asymmetry in the wave amplitude and the frequency spectrum. The frequency spectrum does n. . .
Date: 12/2016 Publisher: Geophysical Research Letters DOI: 10.1002/2016GL071158 Available at: http://onlinelibrary.wiley.com/doi/10.1002/2016GL071158/full
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2015
Authors: Stephens G. K., Sitnov M I, Ukhorskiy A Y, Roelof E. C., Tsyganenko N A, et al.
Title: Empirical modeling of the storm-time innermost magnetosphere using Van Allen Probes and THEMIS data: Eastward and banana currents
Abstract: The structure of storm-time currents in the inner magnetosphere, including its innermost region inside 4RE, is studied for the first time using a modification of the empirical geomagnetic field model TS07D and new data from Van Allen Probes and THEMIS missions. It is shown that the model, which uses basis-function expansions instead of ad hoc current modules to approximate the magnetic field, consistently improves its resolution and magnetic field reconstruction with the increase of the number of basis functions and resolves the spatial structure and evolution of the innermost eastward current. This includes a connection between the westward ring current flowing largely at inline image and the eastward ring current concentrated at inline image resulting in a vortex current pattern. A simil. . .
Date: 01/2015 Publisher: Journal of Geophysical Research: Space Physics Pages: n/a - n/a DOI: 10.1002/2015JA021700 Available at: http://doi.wiley.com/10.1002/2015JA021700
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Authors: Nosé M., Oimatsu S., Keika K, Kletzing C A, Kurth W S, et al.
Title: Formation of the oxygen torus in the inner magnetosphere: Van Allen Probes observations
Abstract: We study the formation process of an oxygen torus during the 12–15 November 2012 magnetic storm, using the magnetic field and plasma wave data obtained by Van Allen Probes. We estimate the local plasma mass density (ρL) and the local electron number density (neL) from the resonant frequencies of standing Alfvén waves and the upper hybrid resonance band. The average ion mass (M) can be calculated by M ∼ ρL/neL under the assumption of quasi-neutrality of plasma. During the storm recovery phase, both Probe A and Probe B observe the oxygen torus at L = 3.0–4.0 and L = 3.7–4.5, respectively, on the morning side. The oxygen torus has M = 4.5–8 amu and extends around the plasmapause that is identified at L∼3.2–3.9. We find that during the initial phase, M is 4–7 amu throughout . . .
Date: 02/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2014JA020593 Available at: http://doi.wiley.com/10.1002/2014JA020593
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Authors: Kataoka Ryuho, Shiota Daikou, Kilpua Emilia, and Keika Kunihiro
Title: Pileup accident hypothesis of magnetic storm on 17 March 2015
Abstract: We propose a “pileup accident” hypothesis, based on the solar wind data analysis and magnetohydrodynamics modeling, to explain unexpectedly geoeffective solar wind structure which caused the largest magnetic storm so far during the solar cycle 24 on 17 March 2015: First, a fast coronal mass ejection with strong southward magnetic fields both in the sheath and in the ejecta was followed by a high-speed stream from a nearby coronal hole. This combination resulted in less adiabatic expansion than usual to keep the high speed, strong magnetic field, and high density within the coronal mass ejection. Second, preceding slow and high-density solar wind was piled up ahead of the coronal mass ejection just before the arrival at the Earth to further enhance its magnetic field and density. Finall. . .
Date: 07/2015 Publisher: Geophysical Research Letters DOI: 10.1002/2015GL064816 Available at: http://doi.wiley.com/10.1002/2015GL064816
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Authors: Zhang J.-C., Kistler L. M., Spence H E, Wolf R. A., Reeves G., et al.
Title: “Trunk-like” heavy ion structures observed by the Van Allen Probes
Abstract: Dynamic ion spectral features in the inner magnetosphere are the observational signatures of ion acceleration, transport, and loss in the global magnetosphere. We report “trunk-like” ion structures observed by the Van Allen Probes on 2 November 2012. This new type of ion structure looks like an elephant's trunk on an energy-time spectrogram, with the energy of the peak flux decreasing Earthward. The trunks are present in He+ and O+ ions but not in H+. During the event, ion energies in the He+ trunk, located at L = 3.6–2.6, MLT = 9.1–10.5, and MLAT = −2.4–0.09°, vary monotonically from 3.5 to 0.04 keV. The values at the two end points of the O+ trunk are: energy = 4.5–0.7 keV, L = 3.6–2.5, MLT = 9.1–10.7, and MLAT = −2.4–0.4°. Results from backward ion drift path tra. . .
Date: 10/2015 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2015JA021822 Available at: http://doi.wiley.com/10.1002/2015JA021822http://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2F2015JA021822
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2013
Authors: Artemyev A. V., Agapitov O. V., Mourenas D., Krasnoselskikh V., and Zelenyi L. M.
Title: Storm-induced energization of radiation belt electrons: Effect of wave obliquity
Abstract: New Cluster statistics allow us to determine for the first time the variations of both the obliquity and intensity of lower-band chorus waves as functions of latitude and geomagnetic activity near L∼5. The portion of wave power in very oblique waves decreases during highly disturbed periods, consistent with increased Landau damping by inward-penetrating suprathermal electrons. Simple analytical considerations as well as full numerical calculations of quasi-linear diffusion rates demonstrate that early-time electron acceleration occurs in a regime of loss-limited energization. In this regime, the average wave obliquity plays a critical role in mitigating lifetime reduction as wave intensity increases with geomagnetic activity, suggesting that much larger energization levels should be reac. . .
Date: 08/2013 Publisher: Geophysical Research Letters Pages: 4138 - 4143 DOI: 10.1002/grl.50837 Available at: http://doi.wiley.com/10.1002/grl.50837
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