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Found 41 entries in the Bibliography.
Showing entries from 1 through 41
| 2019 |
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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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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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Plasma kinetic theory predicts that sufficiently anisotropic proton distribution will excite electromagnetic ion cyclotron (EMIC) waves, which in turn relax the proton distribution to a marginally stable state creating an upper bound on the relaxed proton anisotropy. Here, using EMIC wave observations and coincident plasma measurements made by Van Allen Probes in the inner magnetosphere, we show that the proton distributions are well constrained by this instability to a marginally stable state. Near the threshold, the probability of EMIC wave occurrence is highest, having left-handed polarization and observed near the magnetic equator with relatively small wave normal angles, indicating that these waves are locally generated. In addition, EMIC waves are distributed in two magnetic local time regions with different intensity. Compared with helium band waves, hydrogen band waves behave similarly except that they are often observed in low-density regions. These results reveal several important features regarding EMIC waves excitation and propagation. Yue, Chao; Jun, Chae-Woo; Bortnik, Jacob; An, Xin; Ma, Qianli; Reeves, Geoffrey; Spence, Harlan; Gerrard, Andrew; Gkioulidou, Matina; Mitchell, Donald; Kletzing, Craig; Published by: Geophysical Research Letters Published on: 04/2019 YEAR: 2019 DOI: 10.1029/2019GL082633 EMIC waves; helium-band; hydrogen-band; plasma beta; proton temperature anisotropy; Van Allen Probes |
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Ion transport from the plasma sheet to the ring current is the main cause of the development of the ring current. Energetic (>150 keV) ring current ions are known to be transported diffusively in several days. A recent study suggested that energetic oxygen ions are transported closer to the Earth than protons due to the diffusive transport caused by a combination of the drift and drift-bounce resonances with Pc 3\textendash5 ultralow frequency waves during the 24 April 2013 magnetic storm. To understand the occurrence conditions of such selective oxygen increase (SOI), we investigate the phase space densities (PSDs) between protons and oxygen ions with the first adiabatic invariants (μ) of 0.1\textendash2.0 keV/nT measured by the Radiation Belt Storm Probes Ion Composition Experiment instrument on the Van Allen Probes at L ~ 3\textendash6 during 90 magnetic storms in 2013\textendash2017. We identified the SOI events in which oxygen PSDs increase while proton PSDs do not increase during a period of ~9 hr (one orbital period). Among the 90 magnetic storms, 33\% were accompanied by the SOI events. Global enhancements of Pc 4 and Pc 5 waves observed by ground magnetometers during the SOI events suggest that radial transport due to combination of the drift-bounce resonance with Pc 4 oscillations and the drift resonance with Pc 5 oscillations can be the cause of SOIs. The contribution of the SOI events to the magnetic storm intensity is roughly estimated to be ~9\% on average. Mitani, K.; Seki, K.; Keika, K.; Gkioulidou, M.; Lanzerotti, L.; Mitchell, D.; Kletzing, C.; Yoshikawa, A.; Obana, Y.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2019 YEAR: 2019 DOI: 10.1029/2018JA026168 Magnetic Storms; Oxygen ions; ring current; Van Allen Probes |
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Low-Energy ( The heavy ion component of the low-energy (eV to hundreds of eV) ion population in the inner magnetosphere, also known as the O+ torus, is a crucial population for various aspects of magnetospheric dynamics. Yet even though its existence has been known since the 1980s, its formation remains an open question. We present a comprehensive study of a low-energy ( Gkioulidou, Matina; Ohtani, S.; Ukhorskiy, A; Mitchell, D.; Takahashi, K.; Spence, H.; Wygant, J.; Kletzing, C.; Barnes, R.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2019 YEAR: 2019 DOI: 10.1029/2018JA025862 |
| 2018 |
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The composition of plasma inside geostationary orbit based on Van Allen Probes observations The composition of the inner magnetosphere is of great importance for determining the plasma pressure, and thus the currents and magnetic field configuration. In this study, we perform a statistical survey of equatorial plasma pressure distributions and investigate the relative contributions of ions and electron with different energies inside of geostationary orbit under two AE levels based on over sixty months of observations from the HOPE and RBSPICE mass spectrometers on board Van Allen Probes. We find that the total and partial pressures of different species increase significantly at high AE levels with Hydrogen (H+) pressure being dominant in the plasmasphere. The pressures of the heavy ions and electrons increase outside the plasmapause and develop a strong dawn-dusk asymmetry with ion pressures peaking at dusk and electron pressure peaking at dawn. In addition, ring current H+ with energies ranging from 50 keV up to several hundred keV is the dominant component of plasma pressure during both quiet (> 90\%) and active times (> 60\%), while Oxygen (O+) with 10 < E < 50 keV and electrons with 0.1 < E < 40 keV become important during active times contributing more than 25\% and 20\% on the nightside, respectively, while the Helium (He+) contribution is generally small. The results presented in this study provide a global picture of the equatorial plasma pressure distributions and the associated contributions from different species with different energy ranges, which advance our knowledge of wave generation and provide models with a systematic baseline of plasma composition. Yue, Chao; Bortnik, Jacob; Li, Wen; Ma, Qianli; Gkioulidou, Matina; Reeves, Geoffrey; Wang, Chih-Ping; Thorne, Richard; T. Y. Lui, Anthony; Gerrard, Andrew; Spence, Harlan; Mitchell, Donald; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2018 YEAR: 2018 DOI: 10.1029/2018JA025344 ion composition; plasma pressure; Plasmapause; Van Allen Probes |
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Evidence of Microbursts Observed Near the Equatorial Plane in the Outer Van Allen Radiation Belt We present the first evidence of electron microbursts observed near the equatorial plane in Earth\textquoterights outer radiation belt. We observed the microbursts on March 31st, 2017 with the Magnetic Electron Ion Spectrometer and RBSP Ion Composition Experiment on the Van Allen Probes. Microburst electrons with kinetic energies of 29-92 keV were scattered over a substantial range of pitch angles, and over time intervals of 150-500 ms. Furthermore, the microbursts arrived without dispersion in energy, indicating that they were recently scattered near the spacecraft. We have applied the relativistic theory of wave-particle resonant diffusion to the calculated phase space density, revealing that the observed transport of microburst electrons is not consistent with the hypothesized quasi-linear approximation. Shumko, Mykhaylo; Turner, Drew; O\textquoterightBrien, T.; Claudepierre, Seth; Sample, John; Hartley, D.; Fennell, Joseph; Blake, Bernard; Gkioulidou, Matina; Mitchell, Donald; Published by: Geophysical Research Letters Published on: 07/2018 YEAR: 2018 DOI: 10.1029/2018GL078451 |
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Much of plasma heating and transport from the magnetotail into the inner magnetosphere occurs in the form of mesoscale discrete injections associated with sharp dipolarizations of magnetic field (dipolarization fronts). In this paper we investigate the role of magnetic trapping in acceleration and transport of the plasmasheet ions into the ring current. For this purpose we use high-resolution global MHD and three-dimensional test-particle simulations. It is shown that trapping, produced by sharp magnetic field gradients at the interface between dipolarizations and the ambient plasma, affect plasmasheet protons with energies above approximately 10 keV, enabling their transport across more than 10 Earth radii and acceleration by a factor of 10. Our estimates show that trapping is important to the buildup of the ring current plasma pressure of injected particles; depending on the plasmasheet temperature and energy spectrum, trapped protons can contribute between 20\% to 60\% of the plasma pressure. It is also shown that the acceleration process does not conserve the particle first invariant; on average protons are accelerated to higher energies compared to a purely adiabatic process. We also investigate how trapping and energization varies for deferent ions species and show that, in accordance with recent observations, ion acceleration is proportional to the ion charge and is independent of its mass. Ukhorskiy, A; Sorathia, K.; Merkin, V.; Sitnov, M.; Mitchell, D.; Gkioulidou, M.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2018 YEAR: 2018 DOI: 10.1029/2018JA025370 injections; plasma pressure; ring current; trapping; Van Allen Probes |
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Response of Different Ion Species to Local Magnetic Dipolarization Inside Geosynchronous Orbit This paper examines how hydrogen, helium and oxygen (H, He and O) ion fluxes at 1\textendash1000 keV typically respond to local magnetic dipolarization inside geosynchronous orbit (GEO). We extracted 144 dipolarizations which occurred at magnetic inclination > 30\textdegree from the 2012\textendash2016 tail seasons\textquoteright observations of the Van Allen Probes spacecraft and then defined typical flux changes of these ion species by performing a superposed epoch analysis. On average, the dipolarization inside GEO is accompanied by a precursory transient decrease in the northward magnetic field component, transient impulsive enhancement in the westward electric field component, and decrease (increase) in the proton density (temperature). The coincident ion species experience an energy-dependent flux change, consisting of enhancement (depression) at energies above (below) ~50 keV. These properties morphologically resemble those around dipolarization fronts (or fast flows) in the near-Earth tail. A distinction among the ion species is the average energy of the flux ratio peak, being at 200\textendash400 keV (100\textendash200 keV) for He (H and O) ions. The flux ratio peaks at different energies likely reflect the different charge states of injected ionospheric- and/or solar wind-origin ion species. The ion spectra become harder for sharp dipolarizations, suggesting the importance of accompanying electric field in transporting and/or energizing the ions efficiently. Interestingly, the average flux ratio peak does not differ significantly among the ion species for ~2 min after onset, which implies that mass-dependent acceleration process is less important in the initial stage of dipolarization. Motoba, T.; Ohtani, S.; Gkioulidou, M.; Ukhorskiy, A.; Mitchell, D.; Takahashi, K.; Lanzerotti, L.; Kletzing, C.; Spence, H.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2018 YEAR: 2018 DOI: 10.1029/2018JA025557 deep inside geosynchronous orbit; dipolarizations; Ion injections; ion species; Van Allen Probes |
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The transport mechanism of the ring current ions differs among ion energies. Lower-energy (≲150 keV) ions are well known to be transported convectively. Higher-energy (≳150 keV) protons are reported to be transported diffusively, while there are few reports about transport of higher-energy oxygen ions. We report the radial transport of higher-energy oxygen ions into the deep inner magnetosphere during the late main phase of the magnetic storm on 23\textendash25 April 2013 observed by the Van Allen Probes spacecraft. An enhancement of 1\textendash100 mHz magnetic fluctuations is simultaneously observed. Observations of 3 and 30 mHz geomagnetic pulsations indicate the azimuthal mode number is <=10. The fluctuations can resonate with the drift and bounce motions of the oxygen ions. The results suggest that the combination of the drift and drift-bounce resonances is responsible for the radial transport of higher-energy oxygen ions. Mitani, K.; Seki, K.; Keika, K.; Gkioulidou, M.; Lanzerotti, L.; Mitchell, D.; Kletzing, C.; Published by: Geophysical Research Letters Published on: 05/2018 YEAR: 2018 DOI: 10.1029/2018GL077500 |
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A poloidal Pc4 wave and proton flux oscillations are observed in the inner magnetosphere on the dayside near the magnetic equator by the Van Allen Probes spacecraft on 2 March 2014. The flux oscillations are observed in the energy range of 67.0 keV to 268.8 keV with the same frequency of the poloidal Pc4 wave. We find pitch angle and energy dispersion in the phase difference between the poloidal magnetic field and the proton flux oscillations, which are features of drift-bounce resonance. We estimate the resonance energy to be ~120 keV for pitch angle (α) of 30\textdegree or 150\textdegree, and 170\textendash180 keV for α = 50\textdegree or 130\textdegree. To examine the direction of energy flow between protons and the wave, we calculate the sign of the gradient of proton phase space density (df/dW) on both the inbound and outbound legs of the orbit. We find the gradient to be outward on both legs, which means that energy is transferred from the protons to the wave. During the poloidal Pc4 wave event, the Dst* index shows a measurable increase of ~6.7 nT. We estimate the total energy loss of the ring current from the recovery of the Dst* index and from the variation of proton flux by the drift-bounce resonance. We suggest that energy transfer from the ring current protons to the poloidal Pc4 wave via the drift-bounce resonance contributes to up to ~85 \% of the increase of the Dst* index. Oimatsu, S.; e, M.; Takahashi, K.; Yamamoto, K.; Keika, K.; Kletzing, C.; Smith, C.; MacDowall, R.; Mitchell, D.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2018 YEAR: 2018 DOI: 10.1029/2017JA025087 |
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We examine the spatiotemporal variations of the energy density and the energy spectral evolution of energetic ions in the inner magnetosphere during the main phase of the 17 March 2015 storm, using data from the RBSPICE and EMFISIS instruments onboard Van Allen Probes. The storm developed in response to two southward IMF intervals separated by about 3 h. In contrast to two steps seen in the Dst/SYM-H index, the ring current ion population evolved in three steps: the first subphase was apparently caused by the earlier southward IMF, and the subsequent subphases occurred during the later southward IMF period. Ion energy ranges that contribute to the ring current differed between the three subphases. We suggest that the spectral evolution resulted from the penetration of different plasma sheet populations. The ring current buildup during the first subphase was caused by the penetration of a relatively low-energy population that had existed in the plasma sheet during a prolonged prestorm northward IMF interval. The deeper penetration of the lower-energy population was responsible for the second subphase. The third subphase, where the storm was unexpectedly intensified to a Dst/SYM-H level of <-200 nT, was caused by the penetration of a hot, dense plasma sheet population. We attribute the hot, dense population to the entry of hot, dense solar wind into the plasma sheet and/or ion heating/acceleration in the near-Earth plasma sheet associated with magnetotail activity such as reconnection and dipolarization. Keika, Kunihiro; Seki, Kanako; e, Masahito; Miyoshi, Yoshizumi; Lanzerotti, Louis; Mitchell, Donald; Gkioulidou, Matina; Manweiler, Jerry; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2018 YEAR: 2018 DOI: 10.1002/2017JA024462 enhancements of oxygen ions of ionospheric origin; plasma transport from the plasma sheet into the inner magnetosphere; RBSPICE; unexpected intensification of the magnetic storm; Van Allen Probes |
| 2017 |
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Energetic proton spectra measured by the Van Allen Probes We test the hypothesis that pitch-angle scattering by electromagnetic ion cyclotron (EMIC) waves can limit ring current proton fluxes. For two chosen magnetic storms, during March 17-20, 2013 and March 17-20, 2015, we measure proton energy spectra in the region 3 <= L <= 6 using the RBSPICE B instrument on the Van Allen Probes. The most intense proton spectra are observed to occur during the recovery periods of the respective storms. Using proton precipitation data from the POES (NOAA and MetOp) spacecraft, we deduce that EMIC wave action was prevalent at the times and L-shell locations of the most intense proton spectra. We calculate limiting ring current proton energy spectra from recently developed theory. Comparisons between the observed proton energy spectra and the theoretical limiting spectra show reasonable agreement. We conclude that the measurements of the most intense proton spectra are consistent with self-limiting by EMIC wave scattering. Summers, Danny; Shi, Run; Engebretson, Mark; Oksavik, Kjellmar; Manweiler, Jerry; Mitchell, Donald; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2017 YEAR: 2017 DOI: 10.1002/2017JA024484 EMIC-wave -proton scattering; proton ring current; Van Allen Probes |
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Understanding the source and loss processes of various plasma populations is greatly aided by having accurate knowledge of their pitch angle distributions (PADs). Here, we statistically analyze ~1 eV to 600 keV hydrogen (H+) PADs near the geomagnetic equator in the inner magnetosphere based on Van Allen Probes measurements, to comprehensively investigate how the H+ PADs vary with different energies, magnetic local times (MLTs), L-shells, and geomagnetic conditions. Our survey clearly indicates four distinct populations with different PADs: (1) a pancake distribution of the plasmaspheric H+ at low L-shells except for dawn sector; (2) a bi-directional field-aligned distribution of the warm plasma cloak; (3) pancake or isotropic distributions of ring current H+; (4) radiation belt particles show pancake, butterfly and isotropic distributions depending on their energy, MLT and L-shell. Meanwhile, the pancake distribution of ring current H+ moves to lower energies as L-shell increases which is primarily caused by adiabatic transport. Furthermore, energetic H+ (> 10 keV) PADs become more isotropic following the substorm injections, indicating wave-particle interactions. The radiation belt H+ butterfly distributions are identified in a narrow energy range of 100 < E < 400 keV at large L (L > 5), which are less significant during quiet times and extend from dusk to dawn sector through midnight during substorms. The different PADs near the equator provide clues of the underlying physical processes that produce the dynamics of these different populations. Yue, Chao; Bortnik, Jacob; Thorne, Richard; Ma, Qianli; An, Xin; Chappell, C.; Gerrard, Andrew; Lanzerotti, Louis; Shi, Quanqi; Reeves, Geoffrey; Spence, Harlan; Mitchell, Donald; Gkioulidou, Matina; Kletzing, Craig; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2017 YEAR: 2017 DOI: 10.1002/2017JA024421 bi-directional field-aligned; H+ Pitch angle distributions; plasmaspheric H+; radiation belt H+; ring current; Van Allen Probes; warm Plasma cloak |
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Previous observations have driven the prevailing assumption in the field that energetic ions measured by an instrument using a bare solid state detector (SSD) are predominantly protons. However, new near-equatorial energetic particle observations obtained between 7 and 12 RE during Phase 1 of the Magnetospheric Multiscale (MMS) mission challenge the validity of this assumption. In particular, measurements by the Energetic Ion Spectrometer (EIS) instruments have revealed that the intensities of heavy ion species (specifically oxygen and helium) dominate those of protons at energies math formula150-220 keV in the middle to outer (>7 RE) magnetosphere. Given that relative composition measurements can drift as sensors degrade in gain, quality cross-calibration agreement between EIS observations and those from the SSD-based Fly\textquoterights Eye Energetic Particle Spectrometer (FEEPS) sensors provides critical support to the veracity of the measurement. Similar observations from the Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) instruments aboard the Van Allen Probes spacecraft extend the ion composition measurements into the middle magnetosphere and reveal a strongly proton-dominated environment at math formula, but decreasing proton intensities at math formula. It is concluded that the intensity dominance of the heavy ions at higher energies (>150 keV) arises from the existence of significant populations of multiply-charged heavy ions, presumably of solar wind origin. Cohen, Ian; Mitchell, Donald; Kistler, Lynn; Mauk, Barry; Anderson, Brian; Westlake, Joseph; Ohtani, Shinichi; Hamilton, Douglas; Turner, Drew; Blake, Bern; Fennell, Joseph; Jaynes, Allison; Leonard, Trevor; Gerrard, Andrew; Lanzerotti, Louis; Allen, Robert; Burch, James; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2017 YEAR: 2017 DOI: 10.1002/2017JA024351 energetic ion composition; magnetospheric ion composition; Magnetospheric Multiscale (MMS); outer magnetosphere; ring current composition; suprathermal ions; Van Allen Probes |
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Ion acceleration at dipolarization fronts in the inner magnetosphere During geomagnetic storms plasma pressure in the inner magnetosphere is controlled by energetic ions of tens to hundreds of keV. Plasma pressure is the source of global storm time currents, which control the distribution of magnetic field and couple the inner magnetosphere and the ionosphere. Recent analysis showed that the buildup of hot ion population in the inner magnetosphere largely occurs in the form of localized discrete injections associated with sharp dipolarizations of magnetic field, similar to dipolarization fronts in the magnetotail. Because of significant differences between the ambient magnetic field and the dipolarization front properties in the magnetotail and the inner magnetosphere, the physical mechanisms of ion acceleration at dipolarization fronts in these two regions may also be different. In this paper we discuss a new acceleration mechanism enabled by stable trapping of ions at the azimuthally localized dipolarization fronts. It is shown that trapping can provide a robust mechanism of ion energization in the inner magnetosphere even in the absence of large electric fields. Ukhorskiy, A; Sitnov, M.; Merkin, V.; Gkioulidou, M.; Mitchell, D.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2017 YEAR: 2017 DOI: 10.1002/2016JA023304 |
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An interesting form of \textquotedblleftzipper-like\textquotedblright magnetosonic waves consisting of two bands of interleaved periodic rising-tone spectra was newly observed by the Van Allen Probes, the Time History of Events and Macroscale Interactions during Substorms (THEMIS), and the Magnetospheric Multiscale (MMS) missions. The two discrete bands are distinct in frequency and intensity; however, they maintain the same periodicity which varies in space and time, suggesting that they possibly originate from one single source intrinsically. In one event, the zipper-like magnetosonic waves exhibit the same periodicity as a constant-frequency magnetosonic wave and an electrostatic emission, but the modulation comes from neither density fluctuations nor ULF waves. A statistical survey based on 3.5 years of multisatellite observations shows that zipper-like magnetosonic waves mainly occur on the dawnside to noonside, in a frequency range between 10 fcp and fLHR. The zipper-like magnetosonic waves may provide a new clue to nonlinear excitation or modulation process, while its cause still remains to be fully understood. Li, J.; Bortnik, J.; Li, W.; Ma, Q.; Thorne, R.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Wygant, J.; Breneman, A.; Thaller, S.; Funsten, H.; Mitchell, D.; Manweiler, J.; Torbert, R.; Le Contel, O.; Ergun, R.; Lindqvist, P.-A.; Torkar, K.; Nakamura, R.; Andriopoulou, M.; Russell, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2017 YEAR: 2017 DOI: 10.1002/2016JA023536 magnetosonic wave; Radiation belt; rising-tone; Van Allen Probes; zipper-like |
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Acceleration at Dipolarization Fronts in the Inner Magnetosphere During geomagnetic storms plasma pressure in the inner magnetosphere is controlled by energetic ions of tens to hundreds keV. Plasma pressure is the source of global storm-time currents, which control the distribution of magnetic field and couple the inner magnetosphere and the ionosphere. Recent analysis showed that the buildup of hot ion population in the inner magnetosphere largely occurs in the form of localized discrete injections associated with sharp dipolarizations of magnetic field, similar to dipolarization fronts in the magnetotail. Because of significant differences between the ambient magnetic field and the dipolarization front properties in the magnetotail and the inner magnetosphere, the physical mechanisms of ion acceleration at dipolarization fronts in these two regions may also be different. In this paper we discuss a new acceleration mechanism enabled by stable trapping of ions at the azimuthally localized dipolarization fronts. It is shown that trapping can provide a robust mechanism of ion energization in the inner magnetosphere even in the absence of large electric fields. Ukhorskiy, A; Sitnov, M.; Merkin, V.; Gkioulidou, M.; Mitchell, D.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2017 YEAR: 2017 DOI: 10.1002/2016ja023304 |
| 2016 |
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The permeability of the magnetopause to a multispecies substorm injection of energetic particles Leakage of ions from the magnetosphere into the magnetosheath remains an important topic in understanding the plasma physics of Earth\textquoterights magnetopause and the interaction of the solar wind with the magnetosphere. Here using sophisticated instrumentation from two spacecraft (Radiation Belt Storm Probes Ion Composition Experiment on the Van Allen Probes and Energetic Ion Spectrometer on the Magnetospheric Multiscale) spaced uniquely near and outside the dayside magnetopause, we are able to determine the escape mechanisms for large gyroradii oxygen ions and much smaller gyroradii hydrogen and helium ions. The oxygen ions are entrained on the magnetosphere boundary, while the hydrogen and helium ions appear to escape along reconnected field lines. These results have important implications for not only Earth\textquoterights magnetosphere but also other solar system magnetospheres. Westlake, J.; Cohen, I.; Mauk, B.; Anderson, B.; Mitchell, D.; Gkioulidou, M.; Walsh, B.; Lanzerotti, L.; Strangeway, R.; Russell, C.; Published by: Geophysical Research Letters Published on: 09/2016 YEAR: 2016 DOI: 10.1002/2016GL070189 energetic particles; magnetopause; magnetosheath; MMSEPD; Van Allen Probes |
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Plasma kinetic theory predicts that a sufficiently anisotropic electron distribution will excite whistler mode waves, which in turn relax the electron distribution in such a way as to create an upper bound on the relaxed electron anisotropy. Here using whistler mode chorus wave and plasma measurements by Van Allen Probes, we confirm that the electron distributions are well constrained by this instability to a marginally stable state in the whistler mode chorus waves generation region. Lower band chorus waves are organized by the electron β||e into two distinct groups: (i) relatively large-amplitude, quasi-parallel waves with inline image and (ii) relatively small-amplitude, oblique waves with inline image. The upper band chorus waves also have enhanced amplitudes close to the instability threshold, with large-amplitude waves being quasi-parallel whereas small-amplitude waves being oblique. These results provide important insight for studying the excitation of whistler mode chorus waves. Yue, Chao; An, Xin; Bortnik, Jacob; Ma, Qianli; Li, Wen; Thorne, Richard; Reeves, Geoffrey; Gkioulidou, Matina; Mitchell, Donald; Kletzing, Craig; Published by: Geophysical Research Letters Published on: 08/2016 YEAR: 2016 DOI: 10.1002/2016GL070084 beta parallel; electron temperature anisotropy; marginally stable state; oblique waves; quasi-parallel waves; Van Allen Probes; whistler mode chorus waves |
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We examine enhancements of energetic (>50 keV) oxygen ions observed by the Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) instrument on board the Van Allen Probes spacecraft in the inner magnetosphere (L ~ 6) at 22\textendash23 h magnetic local time (MLT) during an injection event of the 6 June 2013 storm. Simultaneous observations by two Van Allen Probes spacecraft located close together (~0.5 RE) indicate that particle injections occurred in the premidnight sector (< ~24 h MLT). We also examine the evolution of the proton and oxygen energy spectra at L ~ 6 during the injection event. The spectral slope did not significantly change during the storm. The oxygen phase space density (PSD) was shifted toward higher PSD in a wide range of the first adiabatic invariant. The spectral evolution manifests the characteristics of adiabatic acceleration and density increase of oxygen ions. Warm (0.1\textendash10 keV) oxygen measured by the Helium, Oxygen, Proton, and Electron (HOPE) instrument was enhanced prior to the storm mostly in magnetic field-aligned directions. The most reasonable scenario of this event is that warm oxygen ions that preexisted in the inner magnetosphere were picked up and adiabatically transported and accelerated by spatially localized, temporarily impulsive electric fields. Keika, Kunihiro; Seki, Kanako; e, Masahito; Machida, Shinobu; Miyoshi, Yoshizumi; Lanzerotti, Louis; Mitchell, Donald; Gkioulidou, Matina; Turner, Drew; Spence, Harlan; Larsen, Brian; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2016 YEAR: 2016 DOI: 10.1002/2016JA022384 adiabatic transport from the plasma sheet; oxygen ions of ionospheric origin; preconditions of magnetic storms; preexisting oxygen ions trapped in the inner magnetosphere; Van Allen Probes; Van Allen Probes RBSPICE observations |
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We investigate magnetic field dipolarization in the inner magnetosphere and its associated ion flux variations, using the magnetic field and energetic ion flux data acquired by the Van Allen Probes. From a study of 74 events that appeared at L = 4.5\textendash6.6 between 1 October 2012 and 31 October 2013, we reveal the following characteristics of the dipolarization in the inner magnetosphere: (1) its timescale is approximately 5 min, (2) it is accompanied by strong magnetic fluctuations that have a dominant frequency close to the O+ gyrofrequency, (3) ion fluxes at 20\textendash50 keV are simultaneously enhanced with larger magnitudes for O+ than for H+, (4) after a few minutes of the dipolarization, the flux enhancement at 0.1\textendash5 keV appears with a clear energy-dispersion signature only for O+, and (5) the energy-dispersed O+ flux enhancement appears in directions parallel or anti-parallel to the magnetic field. From these characteristics, we discuss possible mechanisms that can provide selective acceleration to O+ ions at >20 keV. We conclude that O+ ions at L = 5.4\textendash6.6 undergo nonadiabatic local acceleration caused by oscillating electric field associated with the magnetic fluctuations and/or adiabatic convective transport from the plasma sheet to the inner magnetosphere by the impulsive electric field. At L = 4.5\textendash5.4, however, only the former acceleration is plausible. We also conclude that the field-aligned energy-dispersed O+ ions at 0.1\textendash5 keV originate from the ionosphere and are extracted nearly simultaneously to the onset of the dipolarization. e, M.; Keika, K.; Kletzing, C.; Spence, H.; Smith, C.; MacDowall, R.; Reeves, G.; Larsen, B.; Mitchell, D.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2016 YEAR: 2016 DOI: 10.1002/2016JA022549 Dipolarization; inner magnetosphere; ionospheric outflow; Magnetic Fluctuation; O+ Acceleration; substorm; Van Allen Probes |
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The Source of O + in the Storm-time Ring Current A stretched and compressed geomagnetic field occurred during the main phase of a geomagnetic storm on 1 June 2013. During the storm the Van Allen Probes spacecraft made measurements of the plasma sheet boundary layer, and observed large fluxes of O+ ions streaming up the field line from the nightside auroral region. Prior to the storm main phase there was an increase in the hot (>1 keV) and more isotropic O+ions in the plasma sheet. In the spacecraft inbound pass through the ring current region during the storm main phase, the H+ and O+ ions were significantly enhanced. We show that this enhanced inner magnetosphere ring current population is due to the inward adiabatic convection of the plasma sheet ion population. The energy range of the O+ ion plasma sheet that impacts the ring current most is found to be from ~5 to 60 keV. This is in the energy range of the hot population that increased prior to the start of the storm main phase, and the ion fluxes in this energy range only increase slightly during the extended outflow time interval. Thus, the auroral outflow does not have a significant impact on the ring current during the main phase. The auroral outflow is transported to the inner magnetosphere, but does not reach high enough energies to affect the energy density. We conclude that the more energetic O+ that entered the plasma sheet prior to the main phase and that dominates the ring current is likely from the cusp. Kistler, L.M.; Mouikis, C.; Spence, H.E.; Menz, A.M.; Skoug, R.M.; Funsten, H.O.; Larsen, B.A.; Mitchell, D.G.; Gkioulidou, M.; Wygant, J.R.; Lanzerotti, L.J.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2016 YEAR: 2016 DOI: 10.1002/2015JA022204 Geomagnetic storm; Ionosphere; oxygen; plasma sheet; Plasma Sources; ring current; Van Allen Probes |
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A statistical study of ring current-energy proton pitch angle distributions (PADs) in Earth\textquoterights inner magnetosphere is reported here. The data are from the Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) on board the Van Allen Probe B spacecraft from January 1, 2013 to April 15, 2015. By fitting the data to the functional form sinnα, where α is the proton pitch angle, we examine proton PADs at the energies 50, 100, 180, 328 and 488 keV in the L-shell range from L = 2.5 to L = 6. Three PAD types are classified: trapped (90\textdegree peaked), butterfly and isotropic. The proton PAD dependence on the particle energy, MLT, L-shell, and geomagnetic activity are analyzed in detail. The results show a strong dependence of the proton PADs on MLT. On the nightside, the n values outside the plasmapause are clearly lower than those inside the plasmapause. At higher energies and during intense magnetic activity, nightside butterfly PADs can be observed at L-shells down to the vicinity of the plasmapause. The averaged n values on the dayside are larger than on the nightside. A maximum of the averagedn values occurs around L = 4.5 in the postnoon sector (12 - 16MLT). The averaged n values show a dawn-dusk asymmetry with lower values on the dawnside at high L-shells, which is consistent with previous studies of butterfly PADs. The MLT dependence of the proton PADs becomes more distinct with increasing particle energy. These features suggest that drift-shell splitting coupled with a radial flux gradient play an important role in the formation of PADs, particularly at L > ~ 4.5 Shi, Run; Summers, Danny; Ni, Binbin; Manweiler, Jerry; Mitchell, Donald; Lanzerotti, Louis; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2016 YEAR: 2016 DOI: 10.1002/2015JA022140 |
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Our investigation of the long-term ring current proton pressure evolution in Earth\textquoterights inner magnetosphere based on Van Allen Probes data shows drastically different behavior of the low- and high- energy components of the ring current proton population with respect to theSYM-H index variation. We found that while the low-energy component of the protons (<80 keV) is strongly governed by convective timescales and is very well correlated with the absolute value of SYM-H index, the high-energy component (>100 keV) varies on much longer timescales and shows either no correlation or anticorrelation with the absolute value of SYM-H index. Our study also shows that the contributions of the low- and high- energy protons to the inner magnetosphere energy content are comparable. Thus, our results conclusively demonstrate that proton dynamics, and as a result the energy budget in the inner magnetosphere, do not vary strictly on storm time timescales as those are defined by the SYM-H index. Gkioulidou, Matina; Ukhorskiy, A.; Mitchell, D.; Lanzerotti, L.; Published by: Geophysical Research Letters Published on: 05/2016 YEAR: 2016 DOI: 10.1002/2016GL068013 energy budget; Geomagnetic storms; inner magnetosphere; ring current; Van Allen Probes |
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Ring current electron dynamics during geomagnetic storms based on the Van Allen Probes measurements Based on comprehensive measurements from Helium, Oxygen, Proton, and Electron Mass Spectrometer Ion Spectrometer, Relativistic Electron-Proton Telescope, and Radiation Belt Storm Probes Ion Composition Experiment instruments on the Van Allen Probes, comparative studies of ring current electrons and ions are performed and the role of energetic electrons in the ring current dynamics is investigated. The deep injections of tens to hundreds of keV electrons and tens of keV protons into the inner magnetosphere occur frequently; after the injections the electrons decay slowly in the inner belt but protons in the low L region decay very fast. Intriguing similarities between lower energy protons and higher-energy electrons are also found. The evolution of ring current electron and ion energy densities and energy content are examined in detail during two geomagnetic storms, one moderate and one intense. The results show that the contribution of ring current electrons to the ring current energy content is much smaller than that of ring current ions (up to ~12\% for the moderate storm and ~7\% for the intense storm), and <35 keV electrons dominate the ring current electron energy content at the storm main phases. Though the electron energy content is usually much smaller than that of ions, the enhancement of ring current electron energy content during the moderate storm can get to ~30\% of that of ring current ions, indicating a more dynamic feature of ring current electrons and important role of electrons in the ring current buildup. The ring current electron energy density is also shown to be higher at midnight and dawn while lower at noon and dusk. Zhao, H.; Li, X.; Baker, D.; Claudepierre, S.; Fennell, J.; Blake, J.; Larsen, B.; Skoug, R.; Funsten, H.; Friedel, R.; Reeves, G.; Spence, H.; Mitchell, D.; Lanzerotti, L.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2016 YEAR: 2016 DOI: 10.1002/2016JA022358 deep injections; Geomagnetic storms; ring current; ring current energy content; ring current electrons; Van Allen Probes |
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Our investigation of the long-term ring current proton pressure evolution in Earth\textquoterights inner magnetosphere based on Van Allen Probes data shows drastically different behavior of the low- and high- energy components of the ring current proton population with respect to the Sym-H index variation. We found that while the low-energy component of the protons (<80 keV) is strongly governed by convective timescales and is very well correlated with the absolute value of Sym-H index, the high-energy component (>100 keV) varies on much longer timescales and shows either no or anti-correlation with the absolute value of Sym-H index. Our study also shows that the contributions of the low- and high- energy protons to the inner magnetosphere energy content are comparable. Thus, our results conclusively demonstrate that proton dynamics, and as a result the energy budget in the inner magnetosphere, do not vary strictly on storm-time timescales as those are defined by the Sym-H index. Gkioulidou, Matina; Ukhorskiy, A.; Mitchell, D.; Lanzerotti, L.; Published by: Geophysical Research Letters Published on: 03/2016 YEAR: 2016 DOI: 10.1002/2016GL068013 energy budget; Geomagnetic storms; inner magnetosphere; ring current; Van Allen Probes |
| 2015 |
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Magnetotail processes and structures related to substorm growth phase/onset auroral arcs remain poorly understood mostly due to the lack of adequate observations. In this study we make a comparison between ground-based optical measurements of the premidnight growth phase/onset arcs at subauroral latitudes and magnetically conjugate measurements made by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) at ~780 km in altitude and by the Van Allen Probe B (RBSP-B) spacecraft crossing L values of ~5.0\textendash5.6 in the premidnight inner tail region. The conjugate observations offer a unique opportunity to examine the detailed features of the arc location relative to large-scale Birkeland currents and of the magnetospheric counterpart. Our main findings include (1) at the early stage of the growth phase the quiet auroral arc emerged ~4.3\textdegree equatorward of the boundary between the downward Region 2 (R2) and upward Region 1 (R1) currents; (2) shortly before the auroral breakup (poleward auroral expansion) the latitudinal separation between the arc and the R1/R2 demarcation narrowed to ~1.0\textdegree; (3) RBSP-B observed a magnetic field signature of a local upward field-aligned current (FAC) connecting the arc with the near-Earth tail when the spacecraft footprint was very close to the arc; and (4) the upward FAC signature was located on the tailward side of a local plasma pressure increase confined near L ~5.2\textendash5.4. These findings strongly suggest that the premidnight arc is connected to highly localized pressure gradients embedded in the near-tail R2 source region via the local upward FAC. Motoba, T.; Ohtani, S.; Anderson, B.; Korth, H.; Mitchell, D.; Lanzerotti, L.; Shiokawa, K.; Connors, M.; Kletzing, C.; Reeves, G.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2015 YEAR: 2015 DOI: 10.1002/jgra.v120.1010.1002/2015JA021676 FACs; growth phase/onset arc; M-I coupling; Van Allen Probes |
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Enabled by the comprehensive measurements from the MagEIS, HOPE, and RBSPICE instruments onboard Van Allen Probes in the heart of the radiation belt, the relative contributions of ions with different energies and species to the ring current energy density and their dependence on the phases of geomagnetic storms are quantified. The results show that lower energy (<50 keV) protons enhance much more often and also decay much faster than higher energy protons. During the storm main phase, ions with energies < 50 keV contribute more significantly to the ring current than those with higher energies; while the higher energy protons dominate during the recovery phase and quiet times. The enhancements of higher energy proton fluxes as well as energy content generally occur later than those of lower energy protons, which could be due to the inward radial diffusion. For the March 29, 2013 storm we investigated in detail, the contribution from O+ is ~25\% of the ring current energy content during the main phase, and the majority of that comes from < 50 keV O+. This indicates that even during moderate geomagnetic storms the ionosphere is still an important contributor to the ring current ions. Using the Dessler-Parker-Sckopke relation, the contributions of ring current particles to the magnetic field depression during this geomagnetic storm are also calculated. The results show that the measured ring current ions contribute about half of the Dst depression. Zhao, H.; Li, X.; Baker, D.; Fennell, J.; Blake, J.; Larsen, B.; Skoug, R.; Funsten, H.; Friedel, R.; Reeves, G.; Spence, H.; Mitchell, D.; Lanzerotti, L.; Rodriguez, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2015 YEAR: 2015 DOI: 10.1002/2015JA021533 Geomagnetic storms; Ring current energy content; Ring current ions; The DPS relation; The Dst index; Van Allen Probes |
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The global context of the 14 November, 2012 storm event From 2 to 5 UT on 14 November, 2012, the Van Allen Probes observed repeated particle flux dropouts during the main phase of a geomagnetic storm as the satellites traversed the post-midnight to dawnside inner magnetosphere. Each flux dropout corresponded to an abrupt change in the magnetic topology, i.e., from a more dipolar configuration to a configuration with magnetic field lines stretched in the dawn-dusk direction. Geosynchronous GOES spacecraft located in the dusk and near-midnight sectors and the LANL constellation with wide local time coverage also observed repeated flux dropouts and stretched field lines with similar occurrence patterns to those of the Van Allen Probe events. THEMIS recorded multiple transient abrupt expansions of the evening-side magnetopause ~20\textendash30 min prior to the sequential Van Allen Probes observations. Ground-based magnetograms and all sky images demonstrate repeatable features in conjunction with the dropouts. We combine the various in-situ and ground-based measurements to define and understand the global spatiotemporal features associated with the dropouts observed by the Van Allen Probes. We discuss various proposed hypotheses for the mechanism that plausibly caused this storm-time dropout event as well as formulate a new hypothesis that explains the combined in-situ and ground-based observations: the earthward motion of magnetic flux ropes containing lobe plasmas that form along an extended magnetotail reconnection line in the near-Earth plasma sheet. Hwang, K.-J.; Sibeck, D.; Fok, M.-C.; Zheng, Y.; Nishimura, Y.; Lee, J.-J.; Glocer, A.; Partamies, N.; Singer, H.; Reeves, G.; Mitchell, D.; Kletzing, C.; Onsager, T.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2015 YEAR: 2015 DOI: 10.1002/2014JA020826 |
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We report, for the first time, an auroral undulation event on 1 May 2013 observed by an all-sky imager (ASI) at Athabasca (L = 4.6), Canada, for which in situ field and particle measurements in the conjugate magnetosphere were available from a Van Allen Probes spacecraft. The ASI observed a train of auroral undulation structures emerging spontaneously in the pre-midnight subauroral ionosphere, during the growth phase of a substorm. The undulations had an azimuthal wavelength of ~180 km and propagated westward at a speed of 3\textendash4 km s-1. The successive passage over an observing point yielded quasi-periodic oscillations in diffuse auroral emissions with a period of ~40 s. The azimuthal wave number m of the auroral luminosity oscillations was found to be m ~ -103. During the event the spacecraft \textendash being on tailward stretched field lines ~0.5 RE outside the plasmapause that mapped into the ionosphere conjugate to the auroral undulations \textendash encountered intense poloidal ULF oscillations in the magnetic and electric fields. We identify the field oscillations to be the second harmonic mode along the magnetic field line through comparisons of the observed wave properties with theoretical predictions. The field oscillations were accompanied by oscillations in proton and electron fluxes. Most interestingly, both field and particle oscillations at the spacecraft had one-to-one association with the auroral luminosity oscillations around its footprint. Our findings strongly suggest that this auroral undulation event is closely linked to the generation of second harmonic poloidal waves Motoba, T.; Takahashi, K.; Ukhorskiy, A.; Gkioulidou, M.; Mitchell, D.; Lanzerotti, L.; Korotova, G.; Donovan, E.; Wygant, J.; Kletzing, C.; Kurth, W.; Blake, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2015 YEAR: 2015 DOI: 10.1002/2014JA020863 |
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Recent results by the Van Allen Probes mission showed that the occurrence of energetic ion injections inside geosynchronous orbit could be very frequent throughout the main phase of a geomagnetic storm. Understanding, therefore, the formation and evolution of energetic particle injections is critical in order to quantify their effect in the inner magnetosphere. We present a case study of a substorm event that occurred during a weak storm (Dst ~ - 40 nT) on 14 July 2013. Van Allen Probe B, inside geosynchronous orbit, observed two energetic proton injections within ten minutes, with different dipolarization signatures and duration. The first one is a dispersionless, short timescale injection pulse accompanied by a sharp dipolarization signature, while the second one is a dispersed, longer timescale injection pulse accompanied by a gradual dipolarization signature. We combined ground magnetometer data from various stations, and in-situ particle and magnetic field data from multiple satellites in the inner magnetosphere and near-Earth plasma sheet to determine the spatial extent of these injections, their temporal evolution, and their effects in the inner magnetosphere. Our results indicate that there are different spatial and temporal scales at which injections can occur in the inner magnetosphere and depict the necessity of multipoint observations of both particle and magnetic field data in order to determine these scales. Gkioulidou, Matina; Ohtani, S.; Mitchell, D.; Ukhorskiy, A.; Reeves, G.; Turner, D.; Gjerloev, J.; e, Nos\; Koga, K.; Rodriguez, J.; Lanzerotti, L.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2015 YEAR: 2015 DOI: 10.1002/2014JA020872 |
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On the use of drift echoes to characterize on-orbit sensor discrepancies We describe a method for using drift echo signatures in on-orbit data to resolve discrepancies between different measurements of particle flux. The drift period has a well-defined energy dependence, which gives rise to time dispersion of the echoes. The dispersion can then be used to determine the effective energy for one or more channels given each channel\textquoterights drift period and the known energy for a reference channel. We demonstrate this technique on multiple instruments from the Van Allen probes mission. Drift echoes are only easily observed at high energies (100s keV to multiple MeV), where several drift periods occur before the observing satellite has moved on or the global magnetic conditions have changed. We describe a first-order correction for spacecraft motion. The drift echo technique has provided a significant clue in resolving substantial flux discrepancies between two instruments measuring fluxes near 2 MeV. O\textquoterightBrien, T.P.; Claudepierre, S.G.; Looper, M.D.; Blake, J.B.; Fennell, J.F.; Clemmons, J.H.; Roeder, J.L.; Kanekal, S.G.; Manweiler, J.W.; Mitchell, D.G.; Gkioulidou, M.; Lanzerotti, L.J.; Spence, H.E.; Reeves, G.D.; Baker, D.N.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2015 YEAR: 2015 DOI: 10.1002/2014JA020859 |
| 2014 |
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H-ion (~45-keV to ~600-keV), He-ion (~65-keV to ~520-keV), and O-ion (~140-keV to ~1130-keV) integral flux measurements, from the Radiation Belt Storm Probe Ion Composition Experiment (RBSPICE) instrument aboard the Van Allan Probes spacecraft B, are reported. These abundance data form a cohesive picture of ring current ions during the first nine months of measurements. Furthermore, the data presented herein are used to show injection characteristics via the He-ion/H-ion abundance ratio and the O-ion/H-ion abundance ratio. Of unique interest to ring current dynamics are the spatial-temporal decay characteristics of the two injected populations. We observe that He-ions decay more quickly at lower L-shells, on the orderof ~0.8-day at L-shells of 3\textendash4, and decay more slowly with higher L-shell, on the order of ~1.7-days at L-shells of 5\textendash6. Conversely, O-ions decay very rapidly (~1.5-hours) across all L-shells. The He-ion decay time are consistent with previously measured and calculated lifetimes associated with charge exchange. The O-ion decay time is much faster than predicted and is attributed to the inclusion of higher energy (>500-keV) O-ions in our decay rate estimation. We note that these measurements demonstrate a compelling need for calculation of high energy O-ion loss rates, which have not been adequately studied in the literature to date. Gerrard, Andrew; Lanzerotti, Louis; Gkioulidou, Matina; Mitchell, Donald; Manweiler, Jerry; Bortnik, Jacob; Keika, Kunihiro; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2014 YEAR: 2014 DOI: 10.1002/2014JA020374 inner magnetosphere; ion decay rates; Spacecraft measurements; Van Allen Probes |
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Energetic particle transport into the inner magnetosphere during geomagnetic storms is responsible for significant plasma pressure enhancement, which is the driver of large-scale currents that control the global electrodynamics within the magnetosphere-ionosphere system. Therefore, understanding the transport of plasma from the tail deep into the near-Earth magnetosphere, as well as the energization processes associated with this transport, is essential for a comprehensive knowledge of the near-Earth space environment. During the main phase of a geomagnetic storm on March 17th 2013 (minimum Dst ~ -137 nT), the Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) instrument on the Van Allen Probes observed frequent, small-scale proton injections deep into the inner nightside magnetosphere in the region L ~ 4 \textendash 6. Although isolated injections have been previously reported inside geosynchronous orbit, the large number of small-scale injections observed in this event suggests that, during geomagnetic storms injections provide a robust mechanism for transporting energetic ions deep into the inner magnetosphere. In order to understand the role that these injections play in the ring current dynamics, we determine the following properties for each injection: i) associated pressure enhancement, ii) the time duration of this enhancement, iii) and the lowest and highest energy channels exhibiting a sharp increase in their intensities. Based on these properties, we estimate the effect of these small-scale injections on the pressure buildup during the storm. We find that this mode of transport could make a substantial contribution to the total energy gain in the storm-time inner magnetosphere. Gkioulidou, Matina; Ukhorskiy, A.; Mitchell, D.; Sotirelis, T.; Mauk, B.; Lanzerotti, L.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2014 YEAR: 2014 DOI: 10.1002/2014JA020096 Geomagnetic storms; Ion injections; ring current; Van Allen Probes |
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Comparison of Energetic Electron Intensities Outside and Inside the Radiation Belts The intensities of energetic electrons (~25 \textendash 800 keV) outside and inside Earth\textquoterights radiation belts are reported using measurements from THEMIS and Van Allen Probes during non-geomagnetic storm periods. Three intervals of current disruption/dipolarization events in August, 2013 were selected for comparison. The following results are obtained. (1) Phase space densities (PSDs) for the equatorially mirroring electron population at three values of the first adiabatic invariant (20, 70, and 200 MeV/G) at the outer radiation belt boundary are found to be one to three orders of magnitude higher than values measured just inside the radiation belt. (2) There is indication that substorm activity leads to PSD increases inside L = 5.5 in less than 1 hr. (3) Evidence for progressive inward transport of enhanced PSDs is found. (4) Reductions and enhancements in the PSDs over L-shells from 3.5 to 6 are found to occur rapidly in ~2 \textendash 3 hrs. These results suggest that (1) continual replenishments are required to maintain high levels of PSD for electrons at these energies, and (2) inward radial transport of these electrons occurs in a fast time scale of a few hrs. T. Y. Lui, A.; Mitchell, D.; Lanzerotti, L.; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2014 YEAR: 2014 DOI: 10.1002/2014JA020049 Dipolarization; energetic electrons; Radiation belts; substorm; Van Allen Probes |
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The Energetic Particle Detector (EPD) Investigation is one of 5 fields-and-particles investigations on the Magnetospheric Multiscale (MMS) mission. MMS comprises 4 spacecraft flying in close formation in highly elliptical, near-Earth-equatorial orbits targeting understanding of the fundamental physics of the important physical process called magnetic reconnection using Earth\textquoterights magnetosphere as a plasma laboratory. EPD comprises two sensor types, the Energetic Ion Spectrometer (EIS) with one instrument on each of the 4 spacecraft, and the Fly\textquoterights Eye Energetic Particle Spectrometer (FEEPS) with 2 instruments on each of the 4 spacecraft. EIS measures energetic ion energy, angle and elemental compositional distributions from a required low energy limit of 20 keV for protons and 45 keV for oxygen ions, up to >0.5 MeV (with capabilities to measure up to >1 MeV). FEEPS measures instantaneous all sky images of energetic electrons from 25 keV to >0.5 MeV, and also measures total ion energy distributions from 45 keV to >0.5 MeV to be used in conjunction with EIS to measure all sky ion distributions. In this report we describe the EPD investigation and the details of the EIS sensor. Specifically we describe EPD-level science objectives, the science and measurement requirements, and the challenges that the EPD team had in meeting these requirements. Here we also describe the design and operation of the EIS instruments, their calibrated performances, and the EIS in-flight and ground operations. Blake et al. (The Flys Eye Energetic Particle Spectrometer (FEEPS) contribution to the Energetic Particle Detector (EPD) investigation of the Magnetospheric Magnetoscale (MMS) Mission, this issue) describe the design and operation of the FEEPS instruments, their calibrated performances, and the FEEPS in-flight and ground operations. The MMS spacecraft will launch in early 2015, and over its 2-year mission will provide comprehensive measurements of magnetic reconnection at Earth\textquoterights magnetopause during the 18 months that comprise orbital phase 1, and magnetic reconnection within Earth\textquoterights magnetotail during the about 6 months that comprise orbital phase 2. Mauk, B.; Blake, J.; Baker, D.; Clemmons, J.; Reeves, G.; Spence, H.; Jaskulek, S.; Schlemm, C.; Brown, L.; Cooper, S.; Craft, J.; Fennell, J.; Gurnee, R.; Hammock, C.; Hayes, J.; Hill, P.; Ho, G.; Hutcheson, J.; Jacques, A.; Kerem, S.; Mitchell, D.; Nelson, K.; Paschalidis, N.; Rossano, E.; Stokes, M.; Westlake, J.; Published by: Space Science Reviews Published on: 06/2014 YEAR: 2014 DOI: 10.1007/s11214-014-0055-5 Magnetic reconnection; Magnetosphere; Magnetospheric multiscale; NASA mission; Particle acceleration; Space plasma |
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Signature modeling for LWIR spectrometer Hyperspectral longwave infrared (LWIR) is used for a variety of targets such as gases and solids with the advantage of day or night data collections. A longwave infrared system must have the ability to convert the radiance data it measures to emissivity prior to running a detection algorithm, commonly called a temperature-emissivity separation (TES) algorithm. Key parts of this TES algorithm are accounting for the reflected down-welling radiation from the atmosphere, upwelling background radiance removal, and most importantly determining the temperature of the material. Accounting for these environmental conditions allows for the data to be processed in emissivity to be used in the detection algorithm. The processed data also allows a baseline to determine where key features exist in the signatures collected. In this paper a new method is introduced to process field collected signatures gathered using the Design \& Prototypes microFTIR Model 102. The issue addressed here is calculating the collected signature from radiance to emissivity using a new technique for estimating the surface temperature of the collected sample. The key component of the TES was created to ensure the collected spectra are processed in emissivity space at a quality that is suitable for the detection library on air and ground LWIR systems. Firpi, Alexer; Oxenrider, Jason; Ramachandran, Vignesh; Mitchell, Herbert; Tzeng, Nigel; Rodriguez, Benjamin; Published by: Published on: 03/2014 YEAR: 2014 DOI: 10.1109/AERO.2014.6836439 hyperspectral imaging; infrared imaging; infrared spectrometers; radiance data conversion |
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He ions contribute to Earth\textquoterights ring current energy and species population density and are important in understanding ion transport and charge exchange processes in the inner magnetosphere. He ion flux measurements made by the Van Allen Probes Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) instrument are presented in this paper. Particular focus is centered on geomagnetically quiet intervals in late 2012 and 2013 that show the flux, L-shell, and energy (65 keV to 518 keV) morphology of ring current He ions between geomagnetic storm injection events. The overall He ion abundance during the first nine months of RBSPICE observations, the appearance of a persistent high energy, low L-shell He ion population, and the temporal evolution of this population all provide new insights into trapped ring current energy He ions. These data provide a unique resource that will be used to provide verifications of, and improvements to, models of He ion transport and loss in Earth\textquoterights ring current region. Gerrard, Andrew; Lanzerotti, Louis; Gkioulidou, Matina; Mitchell, Donald; Manweiler, Jerry; Bortnik, Jacob; Published by: Geophysical Research Letters Published on: 02/2014 YEAR: 2014 DOI: 10.1002/2013GL059175 |
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Rotationally driven zebra stripes in Earth s inner radiation belt Structured features on top of nominally smooth distributions of radiation-belt particles at Earth have been previously associated with particle acceleration and transport mechanisms powered exclusively by enhanced solar-wind activity1, 2, 3, 4. Although planetary rotation is considered to be important for particle acceleration at Jupiter and Saturn5, 6, 7, 8, 9, the electric field produced in the inner magnetosphere by Earth\textquoterights rotation can change the velocity of trapped particles by only about 1\textendash2 kilometres per second, so rotation has been thought inconsequential for radiation-belt electrons with velocities of about 100,000 kilometres per second. Here we report that the distributions of energetic electrons across the entire spatial extent of Earth\textquoterights inner radiation belt are organized in regular, highly structured and unexpected \textquoteleftzebra stripes\textquoteright, even when the solar-wind activity is low. Modelling reveals that the patterns are produced by Earth\textquoterights rotation. Radiation-belt electrons are trapped in Earth\textquoterights dipole-like magnetic field, where they undergo slow longitudinal drift motion around the planet because of the gradient and curvature of the magnetic field. Earth\textquoterights rotation induces global diurnal variations of magnetic and electric fields that resonantly interact with electrons whose drift period is close to 24 hours, modifying electron fluxes over a broad energy range into regular patterns composed of multiple stripes extending over the entire span of the inner radiation belt. Ukhorskiy, A; Sitnov, M.; Mitchell, D.; Takahashi, K; Lanzerotti, L.; Mauk, B.; Published by: Nature Published on: 01/2014 YEAR: 2014 DOI: 10.1038/nature13046 |
| 2013 |
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Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) The Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) on the two Van Allen Probes spacecraft is the magnetosphere ring current instrument that will provide data for answering the three over-arching questions for the Van Allen Probes Program: RBSPICE will determine \textquotedbllefthow space weather creates the storm-time ring current around Earth, how that ring current supplies and supports the creation of the radiation belt populations,\textquotedblright and how the ring current is involved in radiation belt losses. RBSPICE is a time-of-flight versus total energy instrument that measures ions over the energy range from \~20 keV to \~1 MeV. RBSPICE will also measure electrons over the energy range \~25 keV to \~1 MeV in order to provide instrument background information in the radiation belts. A description of the instrument and its data products are provided in this chapter. Mitchell, D.; Lanzerotti, L.; Kim, C.; Stokes, M.; Ho, G.; Cooper, S.; UKHORSKIY, A; Manweiler, J.; Jaskulek, S.; Haggerty, D.; Brandt, P.; SITNOV, M; Keika, K.; Hayes, J.; Brown, L.; Gurnee, R.; Hutcheson, J.; Nelson, K.; Paschalidis, N.; Rossano, E.; Kerem, S.; Published by: Space Science Reviews Published on: 11/2013 YEAR: 2013 DOI: 10.1007/s11214-013-9965-x |
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