Bibliography
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Found 882 entries in the Bibliography.
Showing entries from 201 through 250
| 2019 |
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The past decade transformed our observational understanding of energetic particle processes in near-Earth space. An unprecedented suite of observational systems were in operation including the Van Allen Probes, Arase, MMS, THEMIS, Cluster, GPS, GOES, and LANL-GEO magnetospheric missions. They were supported by conjugate low-altitude measurements on spacecraft, balloons, and ground-based arrays. Together these significantly improved our ability to determine and quantify the mechanisms that control the build-up and subsequent variability of energetic particle intensities in the inner magnetosphere. The high-quality data from NASA\textquoterights Van Allen Probes are the most comprehensive in-situ measurements ever taken in the near-Earth space radiation environment. These observations, coupled with recent advances in radiation belt theory and modeling, including dramatic increases in computational power, has ushered in a new era, perhaps a \textquotedblleftgolden era,\textquotedblright in radiation belt research. We have edited a Journal of Geophysical Research: Space Science Special Collection dedicated to Particle Dynamics in the Earth\textquoterights Radiation Belts in which we gather the most recent scientific findings and understanding of this important region of geospace. This collection includes the results presented at the American Geophysical Union Chapman International Conference in Cascais, Portugal (03/2018) and many other recent and relevant contributions. The present article introduces and review the context, current research, and main questions that motivate modern radiation belt research divided into the following topics: (1) particle acceleration and transport, (2) particle loss, (3) the role of nonlinear processes, (4) new radiation belt modeling capabilities and the quantification of model uncertainties, and (5) laboratory plasma experiments. Ripoll, Jean-Francois; Claudepierre, Seth; Ukhorskiy, Sasha; Colpitts, Chris; Li, Xinlin; Fennell, Joe; Crabtree, Chris; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2019 YEAR: 2019 DOI: 10.1029/2019JA026735 inner magnetosphere; laboratory plasma experiments; Particle acceleration; particle loss; Radiation belts; Van Allen Probes |
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Baker, D.N.; Zhao, H.; Li, X.; Kanekal, S.G.; Jaynes, A.N.; Kress, B.T.; Rodriguez, J.V.; Singer, H.J.; Claudepierre, S.G.; Fennell, J.F.; Hoxie, V.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2019 YEAR: 2019 DOI: 10.1029/2019JA027331 energetic particles; Magnetosphere:Inner; Magnetospheric configuration; Radiation belts; Space weather; Van Allen Probes |
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Direct Observation of Subrelativistic Electron Precipitation Potentially Driven by EMIC Waves Electromagnetic ion cyclotron (EMIC) waves are known to typically cause electron losses into Earth\textquoterights upper atmosphere at >~1 MeV, while the minimum energy of electrons subject to efficient EMIC-driven precipitation loss is unresolved. This letter reports electron precipitation from subrelativistic energies of ~250 keV up to ~1 MeV observed by the Focused Investigations of Relativistic Electron Burst Intensity, Range and Dynamics (FIREBIRD-II) CubeSats, while two Polar Operational Environmental Satellites (POES) observed proton precipitation nearby. Van Allen Probe A detected EMIC waves (~0.7\textendash2.0 nT) over the similar L shell extent of electron precipitation observed by FIREBIRD-II, albeit with a ~1.6 magnetic local time (MLT) difference. Although plasmaspheric hiss and magnetosonic waves were also observed, quasi-linear calculations indicate that EMIC waves were the most efficient in driving the electron precipitation. Quasi-linear theory predicts efficient precipitation at >0.8\textendash1 MeV (due to H-band EMIC waves), suggesting that other mechanisms are required to explain the observed subrelativistic electron precipitation. Capannolo, L.; Li, W.; Ma, Q.; Chen, L.; Shen, X.-C.; Spence, H.; Sample, J.; Johnson, A.; Shumko, M.; Klumpar, D.; Redmon, R.; Published by: Geophysical Research Letters Published on: 11/2019 YEAR: 2019 DOI: 10.1029/2019GL084202 electron precipitation; EMIC waves; FIREBIRD-II; quasi linear theory; Radiation belts; Van Allen Probes; wave particle interactions |
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Earth\textquoterights Van Allen Radiation Belts: From Discovery to the Van Allen Probes Era Discovery of the Earth\textquoterights Van Allen radiation belts by instruments flown on Explorer 1 in 1958 was the first major discovery of the Space Age. The observation of distinct inner and outer zones of trapped megaelectron volt (MeV) particles, primarily protons at low altitude and electrons at high altitude, led to early models for source and loss mechanisms including Cosmic Ray Albedo Neutron Decay for inner zone protons, radial diffusion for outer zone electrons and loss to the atmosphere due to pitch angle scattering. This scattering lowers the mirror altitude for particles in their bounce motion parallel to the Earth\textquoterights magnetic field until they suffer collisional loss. A view of the belts as quasi-static inner and outer zones of energetic particles with different sources was modified by observations made during the Solar Cycle 22 maximum in solar activity over 1989\textendash1991. The dynamic variability of outer zone electrons was measured by the Combined Radiation Release and Effects Satellite launched in July 1990. This variability is caused by distinct types of heliospheric structure that vary with the solar cycle. The launch of the twin Van Allen Probes in August 2012 has provided much longer and more comprehensive measurements during the declining phase of Solar Cycle 24. Roughly half of moderate geomagnetic storms, determined by intensity of the ring current carried mostly by protons at hundreds of kiloelectron volts, produce an increase in trapped relativistic electron flux in the outer zone. Mechanisms for accelerating electrons of hundreds of electron volts stored in the tail region of the magnetosphere to MeVenergies in the trapping region are described in this review: prompt and diffusive radial transport and local acceleration driven by magnetospheric waves. Such waves also produce pitch angle scattering loss, as does outward radial transport, enhanced when the magnetosphere is compressed. While quasilinear simulations have been used to successfully reproduce many essential features of the radiation belt particle dynamics, nonlinear wave-particle interactions are found to be potentially important for causing more rapid particle acceleration or precipitation. The findings on the fundamental physics of the Van Allen radiation belts potentially provide insights into understanding energetic particle dynamics at other magnetized planets in the solar system, exoplanets throughout the universe, and in astrophysical and laboratory plasmas. Computational radiation belt models have improved dramatically, particularly in the Van Allen Probes era, and assimilative forecasting of the state of the radiation belts has become more feasible. Moreover, machine learning techniques have been developed to specify and predict the state of the Van Allen radiation belts. Given the potential Space Weather impact of radiation belt variability on technological systems, these new radiation belt models are expected to play a critical role in our technological society in the future as much as meteorological models do today. Published by: Journal of Geophysical Research: Space Physics Published on: 11/2019 YEAR: 2019 DOI: 10.1029/2018JA025940 Particle acceleration; particle loss; particle transport; Radiation belts; Van Allen Probes; wave-particle interactions |
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Two wave packets of second harmonic poloidal Pc 4 waves with a wave frequency of ~7 mHz were detected by Van Allen Probe A at a radial distance of ~5.8 RE and magnetic local time of 13 hr near the magnetic equator, where plasmaspheric refilling was in progress. Proton butterfly distributions with energy dispersions were also measured at the same time; the proton fluxes at 10-30 keV oscillated with the same frequency as the Pc 4 waves. Using the ion sounding technique, we find that the Pc 4 waves propagated eastward with an azimuthal wave number (m number) of ~220 and ~260 for each wave packet, respectively. Such eastward propagating high-m (m > 100) waves were seldom reported in previous studies. The condition of drift-bounce resonance is well satisfied for the estimated m numbers in both events. Proton phase space density was also examined to understand the wave excitation mechanism. We obtained temporal variations of the energy and radial gradient of the proton phase space density, and find that temporal intensification of the radial gradient can generate the two wave packets. The cold electron density around the spacecraft apogee was > 100 cm-3 in the present events, and hence the eigen-frequency of the Pc 4 waves became lower. This causes the increase of the m number which satisfies the resonance condition of drift-bounce resonance for 10-30 keV protons, and meets the condition for destabilization due to gyro-kinetic effect. Yamamoto, K.; e, Nos\; Keika, K.; Hartley, D.P.; Smith, C.W.; MacDowall, R.J.; Lanzerotti, L.J.; Mitchell, D.G.; Spence, H.E.; Reeves, G.D.; Wygant, J.R.; Bonnell, J.W.; Oimatsu, S.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2019 YEAR: 2019 DOI: 10.1029/2019JA027158 drift-bounce resonance; Geomagnetic storm; plasmasphere; ring current; substorm; ULF wave; Van Allen Probes |
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Effects of a Realistic O + Source on Modeling the Ring Current We use the UNH-IMEF electric field model to simulate the convection of O+ from the near-earth plasma sheet into the ring current during the March 17, 2015 storm. Using Van Allen Probes data from the night side apogee, we reconstruct a realistic O+ source. Modeling this storm using the UNH-IMEF electric field and a dipole magnetic field has previously been found to have good agreement. Using the realistic source along with drift times and charge exchange loss from these results, we model an inbound pass near the peak of the storm where O+ is increasingly dominant over H+. We find that the time-varying realistic O+ source is necessary to reproduce the observed spectral features and the O+ pressure enhancements at low L-shells, while our previous results showed that the H+ was able to be modeled sufficiently with a simple, unchanging boundary condition. Further, our results show that adiabatic convective transport of O+ from the near-earth plasma sheet (L ~6) can explain the observed ring current enhancements. Menz, A.M.; Kistler, L.M.; Mouikis, C.G.; Spence, H.E.; Henderson, M.G.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2019 YEAR: 2019 DOI: 10.1029/2019JA026859 |
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In this report, the relationship between innermost plasmapause locations (Lpp) and initial electron enhancements during both storm and nonstorm (Dst > -30 nT) periods are examined using data from the Van Allen Probes. The geomagnetic storms are classified into coronal mass ejection (CME)-driven and corotating interaction region (CIR)-driven storms to explore their influences on the initial electron enhancements, respectively. We also study nonstorm time electron enhancements and observe frequent, sudden (within two consecutive orbital passes) <400-keV electron enhancements during quiet periods. Our analysis reveals an incredibly cohesive observation that holds regardless of electron energies (~30 keV\textendash2.5 MeV) or geomagnetic conditions: the innermost Lpp is the innermost boundary of the initial energetic electron enhancements. Interestingly, the quantified energy-dependent relationship of the sudden, intense energetic electron enhancements, with respect to the innermost Lpp, also exhibit a very similar trend during both storm and nonstorm periods. In summary, the goal of this report is to provide a comprehensive quantification of this consistent relationship under various geomagnetic conditions, which will also enable better forecast and specification of energetic electrons in the inner magnetosphere. Khoo, L.-Y.; Li, X.; Zhao, H.; Chu, X.; Xiang, Z.; Zhang, K.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2019 YEAR: 2019 DOI: 10.1029/2019JA027412 energetic electron enhancements; Plasmapause; Radiation Belt Dynamics; Van Allen Probes |
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The magnetospheric driver of strong thermal emission velocity enhancement (STEVE) is investigated using conjugate observations when Van Allen Probes\textquoteright footprint directly crossed both STEVE and stable red aurora (SAR) arc. In the ionosphere, STEVE is associated with subauroral ion drift features, including electron temperature peak, density gradient, and westward ion flow. The SAR arc at lower latitudes corresponds to regions inside the plasmapause with isotropic plasma heating, which causes redline-only SAR emission via heat conduction. STEVE corresponds to the sharp plasmapause boundary containing quasi-static subauroral ion drift electric field and parallel-accelerated electrons by kinetic Alfv\ en waves. These parallel electrons could precipitate and be accelerated via auroral acceleration processes powered by Alfv\ en waves propagating along the magnetic field with the plasmapause as a waveguide. The electron precipitation, superimposed on the heat conduction, could explain multiwavelength continuous STEVE emission. The green picket-fence emissions are likely optical manifestations of electron precipitation associated with wave structures traveling along the plasmapause. Chu, Xiangning; Malaspina, David; Gallardo-Lacourt, Bea; Liang, Jun; Andersson, Laila; Ma, Qianli; Artemyev, Anton; Liu, Jiang; Ergun, Robert; Thaller, Scott; Akbari, Hassanali; Zhao, Hong; Larsen, Brian; Reeves, Geoffrey; Wygant, John; Breneman, Aaron; Tian, Sheng; Connors, Martin; Donovan, Eric; Archer, William; MacDonald, Elizabeth; Published by: Geophysical Research Letters Published on: 11/2019 YEAR: 2019 DOI: 10.1029/2019GL082789 aurora; kinetic Alfven wave; Plasmapause; STEVE; subauroral ion drift; table red auroral arc; 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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Storm Time Depletions of Multi-MeV Radiation Belt Electrons Observed at Different Pitch Angles During geomagnetic storms, the rapid depletion of the high-energy (several MeV) outer radiation belt electrons is the result of loss to the interplanetary medium through the magnetopause, outward radial diffusion, and loss to the atmosphere due to wave-particle interactions. We have performed a statistical study of 110 storms using pitch angle resolved electron flux measurements from the Van Allen Probes mission and found that inside of the radiation belt (L* = 3 - 5) the number of storms that result in depletion of electrons with equatorial pitch angle αeq = 30o is higher than number of storms that result in depletion of electrons with equatorial pitch angle αeq = 75o. We conclude that this result is consistent with electron scattering by whistler and electromagnetic ion cyclotron waves. At the outer edge of the radiation belt (L* >= 5.2) the number of storms that result in depletion is also large (~40\textendash50\%), emphasizing the significance of the magnetopause shadowing effect and outward radial transport. Drozdov, A; Aseev, N.; Effenberger, F.; Turner, D.; Saikin, A.; Shprits, Y; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2019 YEAR: 2019 DOI: 10.1029/2019JA027332 EMIC waves; multi-MeV electrons; Radiation belts; Van Allen Probes |
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Using energetic particle and wave measurements from the Van Allen Probes, Polar Orbiting Environmental Satellites (POES), and Geostationary Operational Environmental Satellite (GOES), the acceleration mechanism of ultrarelativistic electrons (>3 MeV) in the center of the outer radiation belt is investigated statistically. A superposed epoch analysis is conducted using 19 storms, which caused flux enhancements of 1.8\textendash7.7 MeV electrons. The evolution of electron phase space density radial profile suggests an energy-dependent acceleration of ultrarelativistic electrons in the outer belt. Especially, for electrons with very high energies (~7 MeV), prevalent positive phase space density radial gradients support inward radial diffusion being responsible for electron acceleration in the center of the outer belt (L*~3\textendash5) during most enhancement events in the Van Allen Probes era. We propose a two-step acceleration process to explain the acceleration of ~7 MeV electrons in the outer belt: intense and sustained chorus waves locally energize core electron populations to ultrarelativistic energies at high L region beyond the Van Allen Probes\textquoteright apogee, followed by inward radial diffusion which further energizes these populations to even higher energies. Statistical results of chorus wave activity inferred from POES precipitating electron measurements as well as core electron populations observed by the Van Allen Probes and GOES support this hypothesis. Zhao, H.; Baker, D.N.; Li, X.; Malaspina, D.M.; Jaynes, A.N.; Kanekal, S.G.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2019 YEAR: 2019 DOI: 10.1029/2019JA027111 Acceleration mechanism; Inward radial diffusion; Local Acceleration; Phase space density; Radiation belts; ultrarelativistic electrons; Van Allen Probes |
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Characteristics and Generation of Low-Frequency Magnetosonic Waves Below the Proton Gyrofrequency We report a Van Allen Probes observation of large-amplitude magnetosonic waves with the peak intensity below the proton gyrofrequency (fcp), which may potentially be misinterpreted as electromagnetic ion cyclotron waves. The frequency spacing of the wave harmonic structure suggests that these magnetosonic waves are excited at a distant source region and propagate radially inward. We also conduct a statistical analysis of low-frequency magnetosonic waves below fcp based on the Van Allen Probes data from October 2012 to December 2018. The spatial distribution shows that these low-frequency magnetosonic emissions are dominantly observed inside the plasmasphere from the prenoon to the midnight sector within 5\textdegree of the geomagnetic equator and typically have modest-to-strong wave amplitudes ranging from tens of pT to hundreds of pT. Our study provides insight into understanding the generation and propagation of these low-frequency magnetosonic waves in the Earth\textquoterights inner magnetosphere. Teng, Shangchun; Li, Wen; Tao, Xin; Ma, Qianli; Shen, Xiaochen; Published by: Geophysical Research Letters Published on: 10/2019 YEAR: 2019 DOI: 10.1029/2019GL085372 Below the proton gyrofrequency; Low frequency magnetosonic wave; Van Allen Probes; wave generation; Wave propagation characteristics |
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Six years of Van Allen Probes data are used to investigate cold plasmaspheric electrons affected by ultralow-frequency (ULF) waves in the inner magnetosphere (L<7) including spatial distributions, occurrence conditions, and resonant energy range. Events exhibit a global distribution within L= 4\textendash7 but preferentially occur at L\~5.5\textendash7 in the dayside, while there is higher occurrence rate in the duskside than dawnside. They can occur under different geomagnetic activities and solar wind velocities (VS), but the occurrence rates are increasing with larger AE, |SYMH|, and VS. These features are closely associated with the generation and propagation of ULF waves in Pc4 (45\textendash150 s) and Pc5 (150\textendash600 s) bands. Combined with electron observations from HOPE instrument, the resonant energies inferred from wave power indicate that cold electrons at ones to hundreds of electron volts can be affected by ULF waves. This study may shed new light on further investigations on the acceleration and transportation of cold plasmaspheric particles that would affect plasmaspheric material release to the Earth\textquoterights magnetosphere and instabilities for exciting various waves. Ren, Jie; Zong, Q.; Zhou, X.; Spence, H.; Funsten, H.; Wygant, J.; Rankin, R.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2019 YEAR: 2019 DOI: 10.1029/2019JA027009 Cold plasmaspheric electrons; drift-bounce resonance; ULF waves; Van Allen Probes; Wave-particle interaction |
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Propagation of EMIC Waves Inside the Plasmasphere: A Two-Event Study Electromagnetic ion cyclotron (EMIC) waves are important for the loss of high-energy electrons in the radiation belt. Based on the measurements of Van Allen Probes, two events during the same storm period are presented to study the propagation of EMIC waves. In the first event, left-handed polarized EMIC waves were observed near the plasmapause, while right-handed waves were observed in the inner plasmasphere. The Poynting flux of the right-hand waves was mainly directed inward and equatorward, and no positive growth rates were obtained in the region of these right-hand waves, indicating the inward propagation of the waves from a higher L-shell. In the second event, the wave vectors were quasi-perpendicular to the background magnetic field inside the plasmaspheric plume but became quasi-parallel outside. This phenomenon can be explained by the refraction of the large density gradient, which qualitatively satisfies Snell\textquoterights law. These observations provide indirect evidence of the inward propagation of the EMIC waves and give a new insight on how density gradients may modify wave properties Wang, G.; Zhang, T.; Gao, Z.; Wu, M; Wang, G.; Schmid, D.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2019 YEAR: 2019 DOI: 10.1029/2019JA027055 density gradient; EMIC wave; inward propagation; refraction; right hand polarization; Snell\textquoterights law; Van Allen Probes |
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RBSP-ECT Combined Spin-Averaged Electron Flux Data Product We describe a new data product combining the spin-averaged electron flux measurements from the Radiation Belt Storm Probes (RBSP) Energetic Particle Composition and Thermal Plasma (ECT) suite on the National Aeronautics and Space Administration\textquoterights Van Allen Probes. We describe the methodology used to combine each of the data sets and produce a consistent set of spectra for September 2013 to the present. Three-minute-averaged flux spectra are provided spanning energies from 15 eV up to 20 MeV. This new data product provides additional utility to the ECT data and offers a consistent cross calibrated data set for researchers interested in examining the dynamics of the inner magnetosphere across a wide range of energies. Boyd, A.; Reeves, G.; Spence, H.; Funsten, H.; Larsen, B.; Skoug, R.; Blake, J.; Fennell, J.; Claudepierre, S.; Baker, D.; Kanekal, S.; Jaynes, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2019 YEAR: 2019 DOI: 10.1029/2019JA026733 |
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Storm-time convection dynamics viewed from optical auroras A series of statistical and event studies have demonstrated that the motion of patches in regions of Patchy Pulsating Aurora (PPA) is very close to, if not exactly, convection. Therefore, 2D maps of PPA motion provide us the opportunity to remotely sense magnetospheric convection with relatively high space and time resolution, subject to uncertainties associated with the mapping between the ionosphere and magnetosphere. In this study, we use THEMIS ASI (All Sky Imager) aurora observations combined with RBSP electric field and magnetic field measurements to explore convection dynamics during storm time. From 0500 UT to 0600 UT on March 19 2015, auroral observations across ~4 h of magnetic local time (MLT) show that increases in the westward velocities of patches are closely related to earthward flow bursts in the inner plasma sheet. Together with the meridian scanning photometer (MSP) data, this suggests that the increase in the westward velocities of PPA patches is caused by earthward-moving ion injection structures carried by the fast earthward flows. Yang, Bing; Donovan, Eric; Liang, Jun; Ruohoniemi, Michael; McWilliams, Kathryn; Spanswick, Emma; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: 10/2019 YEAR: 2019 DOI: 10.1016/j.jastp.2019.105088 Auroral streamer; convection; Fast earthward flows; pulsating aurora; Van Allen Probes |
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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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Variability of Quasilinear Diffusion Coefficients for Plasmaspheric Hiss In the outer radiation belt, the acceleration and loss of high-energy electrons is largely controlled by wave-particle interactions. Quasilinear diffusion coefficients are an efficient way to capture the small-scale physics of wave-particle interactions due to magnetospheric wave modes such as plasmaspheric hiss. The strength of quasilinear diffusion coefficients as a function of energy and pitch angle depends on both wave parameters and plasma parameters such as ambient magnetic field strength, plasma number density, and composition. For plasmaspheric hiss in the magnetosphere, observations indicate large variations in the wave intensity and wave normal angle, but less is known about the simultaneous variability of the magnetic field and number density. We use in situ measurements from the Van Allen Probe mission to demonstrate the variability of selected factors that control the size and shape of pitch angle diffusion coefficients: wave intensity, magnetic field strength, and electron number density. We then compare with the variability of diffusion coefficients calculated individually from colocated and simultaneous groups of measurements. We show that the distribution of the plasmaspheric hiss diffusion coefficients is highly non-Gaussian with large variance and that the distributions themselves vary strongly across the three phase space bins studied. In most bins studied, the plasmaspheric hiss diffusion coefficients tend to increase with geomagnetic activity, but our results indicate that new approaches that include natural variability may yield improved parameterizations. We suggest methods like stochastic parameterization of wave-particle interactions could use variability information to improve modeling of the outer radiation belt. Watt, C.; Allison, H.; Meredith, N.; Thompson, R.; Bentley, S.; Rae, I.; Glauert, S.; Horne, R.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2019 YEAR: 2019 DOI: 10.1029/2018JA026401 empirical; Magnetosphere; parameterization; stochastic; Van Allen Probes; wave-particle interactions |
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Electrons with energies in the keV range play an important role in the dynamics of the inner magnetosphere. Therefore, accurately modeling electron fluxes in this region is of great interest. However, these calculations constitute a challenging task since the lifetimes of electrons that are available have limitations. In this study, we simulate electron fluxes in the energy range of 20 eV to 100 keV to assess how well different electron loss models can account for the observed electron fluxes during the Geospace Environment Modelling Challenge Event of the 2013 St. Patrick\textquoterights Day storm. Three models (Case 1, Case 2, and Case 3) of electron lifetimes due to wave-induced pitch angle scattering are used to compute the fluxes, which are compared with measurements from the Van Allen Probes. The three models consider electron losses due to interactions with whistler mode hiss waves inside the plasmasphere and with whistler mode chorus waves outside the plasmasphere. The Case 1 (historical) model produces excessive loss at low L shells before and after the storm, suggesting that it overestimates losses due to hiss during quiet times. During the storm main phase and early recovery all three models show good agreement with the observations, indicating that losses due to chorus during disturbed times are, in general, well accounted for by the models. Furthermore, the more recent Case 2 and Case 3 models show overall better agreement with the observed fluxes. Ferradas, C.; Jordanova, V.; Reeves, G.; Larsen, B.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2019 YEAR: 2019 DOI: 10.1029/2019JA026649 electron lifetime; electron loss; numerical modeling; pitch angle scattering; Van Allen Probes; Weimer electric field model |
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We use the UNH-IMEF, Weimer 1996, https://doi.org/10.1029/96GL02255 and Volland-Stern electric field models along with a dipole magnetic field to calculate drift paths for particles that reach the Van Allen Probes\textquoteright orbit for two inbound passes during two large geomagnetic storms. We compare the particle access in the models with the observed particle access using both realistic and enhanced solar wind model parameters. To test the accuracy of the drift paths, we estimate the H+ charge exchange loss along these drift paths. While increasing the strength of the model electric field drives particles further inward, improving agreement, energy-dependent cutoffs in the spectra do not agree, indicating that potential patterns for highly disturbed times are inaccurate. While none of the models were able to reproduce the observed features of the more dawnward pass during the 17 March 2013 storm, the UNH-IMEF model with enhanced inputs was able to adequately reproduce the access, charge exchange loss, and H+ particle pressure during the 17 March 2015 storm. Menz, A.M.; Kistler, L.M.; Mouikis, C.G.; Matsui, H.; Spence, H.E.; Thaller, S.A.; Wygant, J.R.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2019 YEAR: 2019 DOI: 10.1029/2019JA026683 |
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Modeling the Electron Flux Enhancement and Butterfly Pitch Angle Distributions on L Shells <2.5 We analyze an energetic electron flux enhancement event in the inner radiation belt observed by Van Allen Probes during an intense geomagnetic storm. The energetic electron flux at L~1.5 increased by a factor of 3 with pronounced butterfly pitch angle distributions (PADs). Using a three-dimensional radiation belt model, we simulate the electron evolution under the impact of radial diffusion, local wave-particle interactions including hiss, very low frequency transmitters, and magnetosonic waves, as well as Coulomb scattering. Consistency between observation and simulation suggests that inward radial diffusion plays a dominant role in accelerating electrons up to 900 keV and transporting the butterfly PADs from higher L shells to form the butterfly PADs at L~1.5. However, local wave-particle interactions also contribute to drive butterfly PADs at L ≳ 1.9. Our study provides a feasible mechanism to explain the electron flux enhancement in the inner belt and the persistent presence of the butterfly PADs at L~1.5. Hua, Man; Li, Wen; Ma, Qianli; Ni, Binbin; Nishimura, Yukitoshi; Shen, Xiao-Chen; Li, Haimeng; Published by: Geophysical Research Letters Published on: 09/2019 YEAR: 2019 DOI: 10.1029/2019GL084822 3-D radial belt modeling; Butterfly pitch angle distribution; Electron flux enhancement; inner belt and slot region; Inward radial diffusion; local wave-particle interactions; Van Allen Probes |
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Analyzing EMIC Waves in the Inner Magnetosphere Using Long-Term Van Allen Probes Observations With 64-month magnetic data from Van Allen Probes, we have studied not only the global distribution, wave normal angle (θ), and ellipticity (ε) of electromagnetic ion cyclotron (EMIC) waves, but also the dependence of their occurrence rates and magnetic amplitudes on the AE* index (the mean value of AE index over previous 1 hr). Our results show that H+ band waves are preferentially detected at 5 <= L <= 6.5, in the noon sector. They typically have small θ (<30\textdegree) and weakly left-hand polarization but become more oblique and linearly polarized at larger magnetic latitudes or L-shells. With the increase of AE* index, their occurrence rate significantly increases in the noon sector, and their source region extends to dusk sector. He+ band waves usually occur in the predawn and morning sectors at 3 <= L <= 4.5. They generally have moderate θ (30 \textdegree - 40\textdegree) and left-hand polarization and also become more oblique and linearly polarized at larger latitudes or L-shells. There is a clear enhancement of occurrence rate and amplitude during active geomagnetic periods, especially in the dusk and evening sectors. O+ band waves mainly occur at 3 <= L <= 4 in the predawn sector. They have either very small θ (<20\textdegree) or very large θ (>50\textdegree), and typically linear or weakly right-hand polarization. During active periods, they mostly occur at the midnight sector and L < 3.5. As a valuable supplement to previous statistical studies, our result provides not only a more compresentive EMIC wave model for evaluating their effects on the radiation belt, but also detailed observational constraints on generation mechanisms of EMIC waves. Chen, Huayue; Gao, Xinliang; Lu, Quanming; Wang, Shui; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2019 YEAR: 2019 DOI: 10.1029/2019JA026965 A long-term statistical work; EMIC wave; inner magnetosphere; spatial distribution; Van Allen Probes; Van Allen Probes observation; Wave fundamental characters |
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The Van Allen Probes have observed both symmetric and asymmetric bipolar electric field structures in the Earth\textquoterights inner magnetosphere. In general, the symmetric bipolar structures are identified as electron-phase space holes, whereas the asymmetric structures are interpreted as electron acoustic double layers (EADLs). The generation mechanism of these EADLs is not entirely understood yet. We have modeled the EADLs observed on 13 November 2012 by Van Allen Probe-B. We performed a fluid simulation of the EADLs and tracked their formation and evolution in the simulation. We found that the localized depletion and enhancement in the electron populations act as a perturbation to excite the symmetric bipolar electron acoustic solitary waves, which later evolve into the EADLs. The Ponderomotive force is found to be the main driver behind transformation of the symmetric electron acoustic solitary waves to EADLs via formation of the electron acoustic shocks. Lotekar, Ajay; Kakad, Amar; Kakad, Bharati; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2019 YEAR: 2019 DOI: 10.1029/2018JA026303 Asymmetric electron acoustic double layers; Electron acoustic shock; Electrostatic solitary wave; Fluid simulation; Van Allen Probes |
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Substorm-Ring Current Coupling: A Comparison of Isolated and Compound Substorms Substorms are a highly variable process, which can occur as an isolated event or as part of a sequence of multiple substorms (compound substorms). In this study we identify how the low-energy population of the ring current and subsequent energization varies for isolated substorms compared to the first substorm of a compound event. Using observations of H+ and O+ ions (1 eV to 50 keV) from the Helium Oxygen Proton Electron instrument onboard Van Allen Probe A, we determine the energy content of the ring current in L-MLT space. We observe that the ring current energy content is significantly enhanced during compound substorms as compared to isolated substorms by \~20\textendash30\%. Furthermore, we observe a significantly larger magnitude of energization (by \~40\textendash50\%) following the onset of compound substorms relative to isolated substorms. Analysis suggests that the differences predominantly arise due to a sustained enhancement in dayside driving associated with compound substorms compared to isolated substorms. The strong solar wind driving prior to onset results in important differences in the time history of the magnetosphere, generating significantly different ring current conditions and responses to substorms. The observations reveal information about the substorm injected population and the transport of the plasma in the inner magnetosphere. Sandhu, J.; Rae, I.; Freeman, M.; Gkioulidou, M.; Forsyth, C.; Reeves, G.; Murphy, K.; Walach, M.-T.; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2019 YEAR: 2019 DOI: 10.1029/2019JA026766 inner magnetosphere; ring current; substorms; Van Allen; Van Allen Probes |
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Empirical Modeling of the Geomagnetosphere for SIR and CME-Driven Magnetic Storms During geomagnetic disturbances, the solar wind arrives in the form of characteristic sequences lasting from tens of hours to days. The most important magnetic storm drivers are the coronal mass ejections (CMEs) and the slow-fast stream interaction regions (SIRs). Previous data-based magnetic field models did not distinguish between these types of the solar wind driving. In the present work we retained the basic structure of the Tsyganenko and Andreeva (2015) model but fitted it to data samples corresponding to (1) SIR-driven storms, (2) CME-driven storms preceded with a shock ahead of the CME, and (3) CME-driven storms without such shocks. The storm time dynamics of the model current systems has been represented using the parametrization method developed by Tsyganenko and Sitnov (2005), based on dynamical variables Wi, calculated from concurrent solar wind characteristics and their previous history. The database included observations of THEMIS, Polar, Cluster, Geotail, and Van Allen Probes missions during 155 storms in 1997\textendash2016. The model current systems drastically differ from each other with respect to decay rate and total current magnitudes. During SIR-induced storms, all current systems saturate, while during CME-induced disturbances, the saturation occurs only for the symmetric ring current and the tail current. The partial ring current parameters are drastically different between SIR- and CME-induced storm sets. In the case of SIR-driven storms, the total partial ring current is comparable with symmetric ring current, whereas for all CME-induced events it is nearly twice higher. The results are compared with GOES 15 magnetometer observations. Published by: Journal of Geophysical Research: Space Physics Published on: 07/2019 YEAR: 2019 DOI: 10.1029/2018JA026008 Magnetic Storms; Magnetosphere; Modeling; Solar wind; spacecraft data; Van Allen Probes |
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Auroral kilometric radiation (AKR) can potentially produce serious damage to space-borne systems by accelerating trapped radiation belt electrons to relativistic energies. Here we examine the global occurrences of AKR emissions in radiation belts based on Van Allen Probes observations from 1 October 2012 to 31 December 2016. The statistical results (1,848 events in total) show that AKR covers a broad region of L= 3\textendash6.5 and 00\textendash24 magnetic local time (MLT), with a higher occurrence on the nightside (20\textendash24 MLT and 00\textendash04 MLT) within L= 5\textendash6.5. All the AKR events are observed to be accompanied with suprathermal (\~1 keV) electron flux enhancements. During active geomagnetic periods, both AKR occurrences and electron injections tend to be more distinct, and AKR emission extends to the dayside. The current study shows that AKR emissions from the remote sources are closely associated with electron injections. Zhao, Wanli; Liu, Si; Zhang, Sai; Zhou, Qinghua; Yang, Chang; He, Yihua; Gao, Zhonglei; Xiao, Fuliang; Published by: Geophysical Research Letters Published on: 07/2019 YEAR: 2019 DOI: 10.1029/2019GL083944 Auroral kilometric radiation; global occurrence; Radiation belt; suprathermal electron flux enhancenments; 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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Saturation Characteristics of Parallel EMIC Waves in the Inner Magnetosphere In this letter, detailed evolution process of parallel electromagnetic ion cyclotron waves in the inner magnetosphere has been investigated through quasilinear theory. A new saturation has been found to occur after the usual first saturation. During the interval between these two saturations, the energy transfers from H+ band to He+ band electromagnetic ion cyclotron waves. Moreover, through a best fitting, we obtain new model parameters for the anisotropy-beta inverse relation of hot H+, which identifies the threshold of ion cyclotron instabilities in the inner magnetosphere. In situ observations of the Van Allen Probe mission also verify these new model parameters. Therefore, our results reveal the evolution process and saturation characteristics of parallel electromagnetic ion cyclotron waves in the inner magnetosphere. Published by: Geophysical Research Letters Published on: 07/2019 YEAR: 2019 DOI: 10.1029/2019GL083630 Anisotropy-beta inverse relation; EMIC waves; Quasilinear theory; RC ions; Van Allen Probes |
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We present a statistical analysis with 100\% duty cycle and non-time-averaged amplitudes of the prevalence and distribution of high-amplitude >50-pT whistler mode waves in the outer radiation belt using 5 years of Van Allen Probes data. Whistler mode waves with high magnetic field amplitudes are most common above L=4.5 and between magnetic local time of 0\textendash14 where they are present approximately 1\textendash6\% of the time. During high geomagnetic activity, high-amplitude whistler mode wave occurrence rises above 25\% in some regions. The dayside population are more common during quiet or moderate geomagnetic activity and occur primarily >5\textdegree from the magnetic equator, while the night-to-dawn population are enhanced during active times and are primarily within 5\textdegree of the magnetic equator. These results are different from the distribution of electric field peaks discussed in our previous paper covering the same time period and spatial range. Our previous study found large-amplitude electric field peaks were common down to L=3.5 and were largely absent from afternoon and near noon. The different distribution of large electric and magnetic field amplitudes implies that the low-L component of whistler mode waves observed previously are primarily highly oblique, while the dayside and high-L populations are primarily field aligned. These results have important implications for modeling radiation belt particle interactions with chorus, as large-amplitude waves interact nonlinearly with electrons, resulting in rapid energization, de-energization, or pitch angle scattering. This also may provide clues regarding the mechanisms which can cause significant whistler mode wave growth up to more than 100 times the average wave amplitude. Tyler, E.; Breneman, A.; Cattell, C.; Wygant, J.; Thaller, S.; Malaspina, D.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2019 YEAR: 2019 DOI: 10.1029/2019JA026913 Magnetosphere; magnetospheric chorus; Radiation belts; Van Allen Probes; whistler wave |
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Temperature Dependence of Plasmaspheric Ion Composition We analyze a database of Dynamics Explorer-1 (DE-1) Retarding Ion Mass Spectrometer densities and temperatures to yield the first explicit measure of how cold ion concentration depends on temperature. We find that cold H+ and He+ concentrations have very weak dependence on temperature, but cold O+ ion concentration increases steeply as these ions become warmer. We demonstrate how this result can aid in analyzing composition data from other satellites without spacecraft potential mitigation, by applying the result to an example using data from the Van Allen Probes mission. Measurement of light ion concentrations above 1 electron volt (eV) are a reasonable proxy for the concentrations of colder (eV) ions. Warmer O+ ion concentrations may be extrapolated to colder temperatures using our fit to the statistical distribution versus temperature. Goldstein, J.; Gallagher, D.; Craven, P.; Comfort, R.; Genestreti, K.; Mouikis, C.; Spence, H.; Kurth, W.; Wygant, J.; Skoug, R.; Larsen, B.; Reeves, G.; De Pascuale, S.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2019 YEAR: 2019 DOI: 10.1029/2019JA026822 composition; plasmasphere: ion; temperature; Van Allen Probes |
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Variability of the Proton Radiation Belt Significant steady but slow variability of radiation belt proton intensity, in the energy range \~19\textendash200 MeV and for L<2.4, has been observed in an empirical model derived from data taken by Van Allen Probes during 2013\textendash2019. It is compared to predictions of a theoretical model based on measured initial and boundary conditions. Two aspects of the variability are considered in detail and require adjustments to model parameters. Observed inward transport of proton intensity maxima near L=1.9 and associated increasing intensity are caused in the model by inward radial diffusion from an external source while conserving the first two adiabatic invariants. The diffusion coefficient is constrained by these observations and is required to have increased near the start of 2015 by a factor \~2. Observed decay of proton intensity at L<1.6 can be caused only in part by energy loss to free and bound electrons in the local plasma and neutral atmosphere. Another, unknown loss mechanism is required to match observed proton decay rates as a function of energy. Accounting for the expected influence of slow radial diffusion at low L, the additional loss should have a mean lifetime near 22 years, independent of L and energy in the range \~19\textendash70 MeV. Several candidate loss mechanisms are considered\textemdashadded plasma or neutral density, elastic Coulomb scattering, plasma wave scattering, field-line curvature scattering, and collision with orbital debris\textemdashbut none are found viable. Published by: Journal of Geophysical Research: Space Physics Published on: 07/2019 YEAR: 2019 DOI: 10.1029/2019JA026754 |
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Relativistic electron flux responses in the inner magnetosphere are investigated for 28 magnetic storms driven by Corotating Interaction Region (CIR) and 27 magnetic storms driven by Coronal Mass Ejection (CME), using data from the Relativistic Electron-Proton Telescope (REPT) instrument on board Van-Allen Probes from Oct-2012 to May-2017. In this present study we analyze the role of CIRs and CMEs in electron dynamics by sorting the electron fluxes in terms of averaged solar wind parameters, L-values, and energies. The major outcomes from our study are: (i) At L = 3 and E = 3.4 MeV, for >70\% cases the electron flux remains stable, while at L = 5, for ~82\% cases it changes with the geomagnetic conditions. (ii) At L = 5, ~53\% of the CIR storms and 30\% of the CME storms show electron flux increase. (iii) At a given L-value, the tendency for the electron flux variation diminishes with the increasing energies for both categories of storms. (iv) In case of CIR driven storms, the electron flux changes are associated with changes in Vsw and Sym-H. (v) At L ~ 3, CME storms show increased electron flux, while at L ~ 5, CIR storms are responsible for the electron flux enhancements. (vi) During CME and CIR driven storms, distinct electron flux variations are observed at L = 3 and L = 5. Pandya, Megha; Veenadhari, B.; Ebihara, Y.; Kanekal, S.G.; Baker, D.N.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2019 YEAR: 2019 DOI: 10.1029/2019JA026771 electron flux; innermagnetosphere; Magnetic Storms; Radiation belt; solar wind driver; Van Allen Probes |
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Using Van Allen Probe Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) wave observations from September 2012 to May 2018, we statistically investigate the distributions of power-weighted wave normal angle (WNA) of fast magnetosonic (MS) waves from L = 2\textendash6 within \textpm15\textdegree geomagnetic latitudes. The spatial distributions show that the MS WNAs are mainly confined within 87\textendash89\textdegree near the geomagnetic equator and decrease with increasing magnetic latitude. Further quantitative investigation demonstrates that the WNAs normally distribute as a mixture of two Gaussian distributions ranging from 85\textdegree to 88\textdegree, and the tangent of it can decrease as a Kappa distribution function when the waves propagate to higher latitudes. Our study completes the survey of spatial distributions of MS WNAs and provides quantitative dependence of the WNA distribution on the magnetic latitude in the inner magnetosphere, which can be readily useful in future global simulations of radiation belt particle dynamics. Zou, Zhengyang; Zuo, Pingbing; Ni, Binbin; Wei, Fengsi; Zhao, Zhengyu; Cao, Xing; Fu, Song; Gu, Xudong; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2019 YEAR: 2019 DOI: 10.1029/2019JA026556 Empirical Model; Fast Magnetosonic Waves; latitudinal dependence; power-weighted wave normal angles; spatial distributions; Van Allen Probes |
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Electromagnetic ion cyclotron (EMIC) waves are understood to be one of the dominant drivers of relativistic electron loss from Earth\textquoterights radiation belts. Theory predicts that the associated gyroresonant wave-particle interaction results in a distinct energy-dependent \textquotedblleftbite-out\textquotedblright signature in the normalized flux distribution of electrons as they are scattered into the loss cone. We identify such signatures along with the responsible EMIC waves captured in situ by the Van Allen Probes on 15\textendash16 February 2017. Using the cold plasma approximation, we predict the pitch-angle cutoffs for the scattering signature for the captured EMIC wave and find it in good agreement with the observed electron bite-out scattering signature. Employing the close conjunction between the Van Allen Probes and THEMIS during this time, we explore the temporal and spatial evolution of the scattering signature, as well as the surrounding wave activity, and find that the scattering signature formed during continued wave activity over a period less than a day. These results are consistent with wave-particle interaction theory and support the hypothesis that EMIC waves are an important mechanism for rapid relativistic electron loss from the radiation belts. Bingley, L.; Angelopoulos, V.; Sibeck, D.; Zhang, X.; Halford, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2019 YEAR: 2019 DOI: 10.1029/2018JA026292 |
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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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Double-peak subauroral ion drifts (DSAIDs), characterized by two high-speed flow channels, is a newly identified flow structure in the subauroral ionosphere. He et al. (2016, https://doi.org/10.1002/2016GL069133) proposed that two region 2 field-aligned currents (R2 FACs) might cause the DSAIDs. However, the underlying physical process that drives the double R2 FACs is unknown. This study reports a DSAIDs event and reveals its magnetospheric drivers. Defense Meteorological Satellite Program F18 satellite observed DSAIDs in the duskside subauroral region, which corresponded well to two low-density troughs and two R2 FACs. The Van Allen Probe B demonstrated that intense substorm ion injections recurrently occurred prior to the formation of DSAIDs, suggesting a potential magnetospheric driver of DSAIDs. Simulation confirms that recurrent ion injections intensify the partial ring current and create double pressure peaks in the near-Earth dusk-to-midnight region, leading two R2 FACs to flow into the ionosphere. The two R2 FACs are thus responsible for the DSAIDs formation. This study unveils the generation mechanism of DSAIDs and deepens the knowledge of the complex magnetosphere-ionosphere system. Wei, Dong; Yu, Yiqun; He, Fei; Published by: Geophysical Research Letters Published on: 06/2019 YEAR: 2019 DOI: 10.1029/2019GL083186 |
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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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Simulation of Prompt Acceleration of Radiation Belt Electrons During the 16 July 2017 Storm We investigate the prompt enhancement of radiation belt electron flux observed by the Relativistic Electron Proton Telescope instrument on board Van Allen Probes following the 16 July 2017 CME-shock compression using MHD-test particle simulations. The prompt enhancements can be explained by the source population interacting with the azimuthally directed electric field impulses induced by CME-shock compressions of the dayside magnetopause. Electrons in drift resonance with the electric field impulse were accelerated by \~ 0.6 MeV on a drift period timescale (in minutes) as the impulse propagated from the dayside to the nightside around the flanks of the magnetosphere. MHD test particle simulation of energization and drift phase bunching, due to the bipolar electric field that accompanies the dayside compression and relaxation, is found to be consistent with Van Allen Probes observations. This study reproduces the energy-dependent drift echoes integrated over pitch angle and observed change in spectra for the first time. Patel, Maulik; Li, Zhao; Hudson, Mary; Claudepierre, Seth; Wygant, John; Published by: Geophysical Research Letters Published on: 06/2019 YEAR: 2019 DOI: 10.1029/2019GL083257 |
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Statistical analysis on plasmatrough exohiss waves from the Van Allen Probes In this study using Van Allen Probe wave observations we investigate the statistical properties of exohiss waves, which are structureless whistler mode waves observed outside the plasmapause. The exohiss waves are identified based on the cold electron number density, frequency distribution, ellipticity, and wave normal angle. The statistical analysis on exohiss wave properties shows that exohiss waves prefer to occur over 3 Zhu, Hui; Gu, Wenyao; Chen, Lunjin; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2019 YEAR: 2019 DOI: 10.1029/2018JA026359 |
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High energy trapped particles in the radiation belts constitute potential threats to the functionality of satellites as they enter into those regions. In the inner radiation belt, the characteristics of high-energy (>20MeV) protons variations during geomagnetic activity times have been studied by implementing four-year (2013-2016) observations of the Van Allen probes. An empirical formula has been used to remove the satellite orbit effect, by which proton fluxes have been normalized to the geomagnetic equator. Case studies show that the region of L<1.7 is relatively stable, while L>1.7 is more dynamic and the most significant variation of proton fluxes occurs at L=2.0. The four-year survey at L=2.0 indicates that for every geomagnetic storm, sharp descent in proton fluxes is accompanied by the corresponding depression of SYM-H index, with a one-to-one correspondence, regardless of the storm intensity. Proton fluxes dropouts are synchronous with SYM-H reduction with similar short timescales. Our observational results reveal that high-energy protons in the inner radiation belt are very dynamic, especially for the outer zone of the inner belt, which is beyond our previous knowledge. Xu, Jiyao; He, Zhaohai; Baker, D.N.; Roth, Ilan; Wang, C.; Kanekal, S.G.; Jaynes, A.N.; Liu, Xiao; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2019 YEAR: 2019 DOI: 10.1029/2018JA026205 geomagnetic activities; high energy proton; Inner radiation belt; one-to-one correspondence; prompt responses; RBSP satellite; Van Allen Probes |
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Based on the measurements of ~100-keV to 10-MeV electrons from the Magnetic Electron Ion Spectrometer (MagEIS) and Relativistic Electron and Proton Telescope (REPT) on the Van Allen Probes, the radiation belt electron energy spectra characterization and evolution have been investigated systematically. The results show that the majority of radiation belt electron energy spectra can be represented by one of three types of distributions: exponential, power law, and bump-on-tail (BOT). The exponential spectra are generally dominant in the outer radiation belt outside the plasmasphere, power law spectra usually appear at high L-shells during injections of lower-energy electrons, and BOT spectra commonly dominate inside the plasmasphere at L>2.5 during relatively quiet times. The main features of three types of energy spectra have also been revealed. Specifically, for the BOT energy spectrum, the energy of local flux maximum usually ranges from approximately hundreds of keV to several MeV and the energy of local flux minimum varies from ~100 keV to ~MeV, both increasing as L-shell decreases, confirming the plasmaspheric hiss wave scattering to be the main mechanism forming the BOT energy spectra. Statistical results using 4-year observations from the Van Allen Probes on the relation between energy spectra and plasmapause location also show that the plasmasphere plays a critical role in shaping radiation belt electron energy spectrum: the peak location of BOT energy spectra is ~1 L-shell inside the minimum plasmapause, where BOT energy spectra mostly form in ~1\textendash2 days as a result of hiss wave scattering. Zhao, H.; Johnston, W.R.; Baker, D.N.; Li, X.; Ni, B.; Jaynes, A.N.; Kanekal, S.G.; Blake, J.B.; Claudepierre, S.G.; Reeves, G.D.; Boyd, A.J.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2019 YEAR: 2019 DOI: 10.1029/2019JA026697 Bump-on-tail energy spectrum; Energy spectrum; Exponential energy spectrum; Plasmapause; Power law energy spectrum; radiation belt electrons; Van Allen Probes |
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A Pc5 wave was simultaneously observed in the ionosphere by EKB radar and in the magnetosphere by both Van Allen Probe spacecraft within a substorm activity. The wave was located in the nightside, in 1.5- to 3-hr magnetic local time sector, and in the region corresponding to the magnetic shells with maximal distances 4.6\textendash7.8 Earth\textquoterights radii. As it was found using both the radar and spacecraft data, the wave had frequency of about 1.8 mHz and azimuthal wave number m≈-10; that is, the wave was westward propagating. The EKB radar data revealed the equatorward wave propagating in the ionosphere, which corresponded to the earthward propagation in the magnetosphere. Furthermore, the field-aligned magnetic component was approximately 2 times larger than both transverse components and accompanied by antiphase pressure oscillations; that is, the wave is compressional and diamagnetic. According to both radar and spacecraft measurements, among two transverse magnetic components, the dominant one was the poloidal. The wave was possibly driven by substorm-injected energetic protons registered by the spacecraft: the proton fluxes were modulated with the wave frequency at energies of about 90 keV, which corresponded to the energy of the drift wave-particle resonance. The wave frequency was much lower than the minimal frequency of the field line resonance calculated using the spacecraft data. We conclude that the wave is not the Alfv\ en mode, but some kind of compressional wave, for example, the drift-compressional mode. Mager, Olga; Chelpanov, Maksim; Mager, Pavel; Klimushkin, Dmitri; Berngardt, Oleg; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2019 YEAR: 2019 DOI: 10.1029/2019JA026541 compressional waves; Pc5; poloidal waves; SUPERDARN; ULF waves; Van Allen Probes |
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Effects of scattering of electrons from whistler chorus waves and of ions due to field line curvature on diffuse precipitating particle fluxes and ionospheric conductance during the large 17 March 2013 storm are examined using the self-consistent Rice Convection Model Equilibrium (RCM-E) model. Electrons are found to dominate the diffuse precipitating particle integrated energy flux, with large fluxes from ~21:00 magnetic local time (MLT) eastward to ~11:00 MLT during the storm main phase. Simulated proton and oxygen ion precipitation due to field line curvature scattering is sporadic and localized, occurring where model magnetic field lines are significantly stretched on the night side at equatorial geocentric radial distances r0 ≳8 RE and/or at r0 ~5.5 to 6.5 RE from dusk to midnight where the partial ring current field has perturbed the magnetic field. The precipitating protons likewise contribute sporadically to the storm time Hall and Pedersen conductance in localized regions whereas the precipitating electrons are the dominate storm time contributor to enhanced Hall and Pedersen conductance at auroral magnetic latitudes on the night and morning side. The RCM-E model can reproduce general features of the Van Allen Probe/MagEIS observed trapped electron differential flux spectrograms over energies of ~37 to 150 keV. The simulations with a parameterized electron loss model also reproduce reasonably well the storm time Defense Meteorological Satellite Program integrated electron energy flux at 850 km at satellite crossings from predawn to midmorning. However, model-data agreement is not as good from dusk to premidnight where there are large uncertainties in the electron loss model. Chen, Margaret; Lemon, Colby; Hecht, James; Sazykin, Stanislav; Wolf, Richard; Boyd, Alexander; Valek, Philip; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2019 YEAR: 2019 DOI: 10.1029/2019JA026545 diffuse aurora; electron and ion precipitation; field-line curvature scattering; inner magnetospheric electric field; ionospheric conductance; simulations and data comparisons; Van Allen Probes |
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Effect of Low-Harmonic Magnetosonic Waves on the Radiation Belt Electrons Inside the Plasmasphere 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 bounce resonance, Landau resonance, and transit time scattering. By performing the Fokker-Planck diffusion simulations, we demonstrate that the bounce resonance with the LH MS waves mainly leads to the butterfly pitch angle distribution of MeV electrons, whereas the Landau resonance and transit time scattering mainly affect energetic electrons in the high-density region. Yu, J.; Li, L; Cui, J.; Cao, J.; Wang, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2019 YEAR: 2019 DOI: 10.1029/2018JA026328 bounce resonance; Electron acceleration; Landau resonance; magnetosonic waves; transit-time scattering; Van Allen Probes |
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Epoch-Based Model for Stormtime Plasmapause Location The output of a plasmapause test particle (PTP) code is used to formulate a new epoch-based plasmapause model. The PTP simulation is run for an ensemble of 60 storms spanning 3 September 2012 to 28 September 2017 and having peak Dst of -60 nT or less, yielding over 7 million model plasmapause locations. Events are automatically identified and epoch times calculated relative to the respective storm peaks. Epoch analysis of the simulated plasmapause is demonstrated to be an effective method to reveal the dynamical phases of plume formation and evolution. The plasmapause radius is found to be strongly correlated with positive solar wind electric field. The epoch-binned PTP data are used to create the first analytical model of the plasmapause that explicitly includes plumes. We obtain this result by employing as basis functions our derived exact solutions for the Volland-Stern convection potential. The analytical plasmapause model depends on epoch time, for moderate and strong storms, and is specified by three main parameters: the duskside plasmapause radius and two tuning coefficients. The epoch-based analytical model is shown to agree to within 0.5 RE with nightside in situ plasmapause crossings by the Van Allen Probes on 17 March 2015. Compared to dayside plume crossings on 26 June 2000, the model agrees within 0.7 RE of radius and 0.8 RE azimuthal distance. This level of agreement is comparable to that achieved by the full dynamic PTP simulation. Goldstein, J.; De Pascuale, S.; Kurth, W.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2019 YEAR: 2019 DOI: 10.1029/2018JA025996 epoch-based model; Plasmapause; plasmasphere; plume; Van Allen Probes |
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Evaluation of Plasma Properties From Chorus Waves Observed at the Generation Region In this study we present an inversion method which provides thermal plasma population parameters from characteristics of chorus emissions only. Our ultimate goal is to apply this method to ground-based data in order to derive the lower-energy boundary condition for many radiation belt models. The first step is to test the chorus inversion method on in situ data of the Van Allen Probes in the generation region. The density and thermal velocity of energetic electrons (few kiloelectron volts to 100 keV) are derived from frequency sweep rate and starting frequencies of chorus emissions through analysis of wave data from the Electric and Magnetic Field Instrument Suite and Integrated Science on board the Van Allen Probes. The nonlinear wave growth theory of Omura and Nunn (2011, https://doi.org/10.1029/2010JA016280) serves as the basis for our inversion method, assuming that the triggering wave is originated by the linear cyclotron instability. We present 16 consecutive rising-tone emissions recorded in the generation region between 11 and 12 UT on 14 November 2012. The results of the inversion are compared with density and thermal velocities (parallel and perpendicular) of energetic electrons derived from the unidirectional flux data of the Helium, Oxygen, Proton, and Electron instrument, showing a good agreement: The normalized root-mean-square deviation between the measured and predicted values are less than \~15\%. We found that the theoretical amplitudes are consistent with the measured ones. The relation between linear and nonlinear wave growth agrees with our basic assumption; namely, linear growth is a preceding process of nonlinear wave growth. We analyze electron distributions at the relativistic resonant energy ranges. asz, Lilla; Omura, Yoshiharu; Lichtenberger, J\; Friedel, Reinhard; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2019 YEAR: 2019 DOI: 10.1029/2018JA026337 chorus inversion; Van Allen Probes; Wave-particle interaction |
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During geomagnetic storms, some fraction of the solar wind energy is coupled via reconnection at the dayside magnetopause, a process that requires a southward interplanetary magnetic field Bz. Through a complex sequence of events, some of this energy ultimately drives the generation of electromagnetic ion cyclotron (EMIC) waves, which can then scatter energetic electrons and ions from the radiation belts. In the event described in this paper, the interplanetary magnetic field remained northward throughout the event, a condition unfavorable for solar wind energy coupling through low-latitude reconnection. While this resulted in SYM/H remaining positive throughout the event (so this may not be considered a storm, in spite of the very high solar wind densities), pressure fluctuations were directly transferred into and then propagated throughout the magnetosphere, generating EMIC waves on global scales. The generation mechanism presumably involved the development of temperature anisotropies via perpendicular pressure perturbations, as evidenced by strong correlations between the pressure variations and the intensifications of the waves globally. Electron precipitation was recorded by the Balloon Array for RBSP Relativistic Electron Losses balloons, although it did not have the same widespread signatures as the waves and, in fact, appears to have been quite patchy in character. Observations from Van Allen Probe A satellite (at postmidnight local time) showed clear butterfly distributions, and it may be possible that the EMIC waves contributed to the development of these distribution functions. Ion precipitation was also recorded by the Polar-orbiting Operational Environmental Satellite satellites, though tended to be confined to the dawn-dusk meridians. Lessard, Marc; Paulson, Kristoff; Spence, Harlan; Weaver, Carol; Engebretson, Mark; Millan, Robyn; Woodger, Leslie; Halford, Alexa; Horne, Richard; Rodger, Craig; Hendry, Aaron; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2019 YEAR: 2019 DOI: 10.1029/2019JA026477 |
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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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We report multi-spacecraft observations of ULF waves from Van Allen Probes (RBSP), Magnetospheric Multiscale (MMS), Time History of Events and Macroscale Interactions during Substorm (THEMIS), and Geostationary Operational Environmental Satellites (GOES). On August 31, 2015, global-scale poloidal waves were observed in data from RBSP-B, GOES and THEMIS from L=4 to L=8 over a wide range of magnetic local time (MLT). The polarization states varied towards purely poloidal polarity. In two consecutive orbits over 18 hours, RBSP-A and RBSP-B recorded gradual variation of the polarization states of the poloidal waves; the ratio (|Ba|/|Br|) decreased from 0.82 to 0.13. After the variation of polarization states, the poloidal ULF waves became very purely poloidal waves, localized in both L and MLT. We identify the poloidal wave as second harmonic mode with a large azimuthal wave number (m) of \textendash232. From RBSP particle measurements we find evidence that the high- m poloidal waves during the polarization variations were powered by inward radial gradients and bump-on-tail ion distributions through the N=1 drift-bounce resonance. Most of the time, the dominant free energy source was inward radial gradients, compared with the positive gradient in the energy distribution of the bump-on-tail ion distributions. Wei, Chao; Dai, Lei; Duan, Suping; Wang, Chi; Wang, YuXian; Published by: Earth and Planetary Physics Published on: 05/2019 YEAR: 2019 DOI: 10.26464/epp2019021 bump-on-tail; inward gradient; polarization rotation; poloidal waves; Van Allen Probes |
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Quenching of Equatorial Magnetosonic Waves by Substorm Proton Injections Near equatorial (fast) magnetosonic waves, characterized by high magnetic compressibility, are whistler-mode emissions destabilized by proton shell/ring distributions. In the past, substorm proton injections are widely known to intensify magnetosonic waves in the inner magnetosphere. Here we report the unexpected observations by the Van Allen Probes of the magnetosonic wave quenching associated with the substorm proton injections under both high- and low-density conditions. The enhanced proton thermal pressure distorted the background magnetic field configuration and the cold plasma density distribution. The reduced phase velocities locally allowed the weak growth or even damping of magnetosonic waves. Meanwhile, the spatially irregularly varying refractive indices might suppress the cumulative growth of magnetosonic waves. For intense injections, this wave quenching region could extend over 2 hr in magnetic local time and 0.5 Earth radii in radial distance. These results provide a new understanding of the generation and distribution of magnetosonic waves. Dai, Guyue; Su, Zhenpeng; Liu, Nigang; Wang, Bin; Zheng, Huinan; Wang, Yuming; Wang, Shui; Published by: Geophysical Research Letters Published on: 05/2019 YEAR: 2019 DOI: 10.1029/2019GL082944 Bernstein mode instability; magnetosonic wave; Radiation belt; ring current; substorm injection; Van Allen Probes; Wave-particle interaction |