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  • 1
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    EMIC wave spatial and coherence scales as determined from multipoint Van Allen Probe measurements (2016)
    Wiley
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    Publication Date: 2016-05-12
    Description: Electromagnetic ion cyclotron (EMIC) waves can provide a strong source of energetic electron pitch angle scattering. These waves are often quite localized, however, thus their spatial extent can have a large effect on their overall scattering efficiency. Using measurements from the dual Van Allen Probes, we examine four EMIC wave events observed simultaneously on the two probes at varying spacecraft separations. Correlation of both the wave amplitude and phase observed at both spacecraft is examined to estimate the active region and coherence scales of the waves. We find well-correlated wave amplitude and amplitude modulation across distances spanning hundreds to thousands of km. Phase coherence persisting 30-60 s is observable during close conjunction events but is lost as spacecraft separations exceed ~1 Earth Radii.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    O+ Ion Conic and Plasma Sheet Dynamics Observed by Van Allen Probe Satellites during the 1 June 2013 Magnetic Storm (2016)
    Wiley
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    Publication Date: 2016-04-09
    Description: The Van Allen Probe satellites were near apogee in the late evening local time sector during the 1 June 2013 magnetic storm's main phase. About an hour after crossing the ring current's “nose structure” into the plasma sheet, the satellites encountered a quasi-periodic sequence of 0.08 - 3 keV O+ ions. Pitch angle distributions of this population consistently peaked nearly anti-parallel to the local magnetic field. We interpret this population as O+ conics originating in the northern ionosphere. Sequences began as fairly steady state conic fluxes with energies in the ~ 80 to 100 eV range. Over about a half hour build-up phase, O+ energies peaked near 1 keV. During subsequent release phases lasting ~ 20 minutes, O+ energies returned to low-energy starting points. We argue these observations reflect repeated formations and dissolutions of downward, magnetically aligned electric fields (ε || ) layers trapping O+ conics between mirror points within heating layers below and electrostatic barriers above [ Gorney et al ., 1985]. Nearly identical variations were observed at the locations of both satellites during 9 of these 13 conic cycles. Phase differences between cycles were observed at both spacecraft during the remaining events. Most “build-up” to “release” phase transitions coincided with AL index minima. However, in situ magnetometer measurements indicate only weak dipolarizations of tail-like magnetic fields. The lack of field-aligned reflected O+ and tail-like magnetic fields suggest that both ionospheres may be active. However, southern hemisphere origin conics cannot be observed since they would be isotropized and accelerated during neutral sheet crossings.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Large-amplitude transmitter-associated and lightning-associated whistler waves in the Earth's inner plasmasphere at L 〈 2 (2011)
    Wiley
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    Publication Date: 2011-06-16
    Description: We report observations of very large amplitude whistler mode waves in the Earth's nightside inner radiation belt enabled by the STEREO Time Domain Sampler. Amplitudes range from 30–110 mV/m (zero-peak), 2 to 3 orders of magnitude larger than previously observed in this region. Measurements from the peak electric field detector (TDSMax) indicate that these large-amplitude waves are prevalent throughout the plasmasphere. A detailed examination of high time resolution electric field waveforms is undertaken on a subset of these whistlers at L 〈 2, associated with pump waves from lightning flashes and the naval transmitter NPM in Hawaii, that become unstable after propagation through the ionosphere and grow to large amplitudes. Many of the waveforms undergo periodic polarization reversals near the lower hybrid and NPM naval transmitter frequencies. The reversals may be related to finite plasma temperature and gradients in density induced by ion cyclotron heating of the plasma at 200 Hz, the modulation frequency of the continuous-mode NPM naval transmitter signal. Test particle simulations using the amplitudes and durations of the waves observed herein suggest that they can interact strongly with high-energy (〉100 keV) electrons on a time scale of
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 4
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    Explaining polarization reversals in STEREO wave data (2012)
    Wiley
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    Publication Date: 2012-04-25
    Description: Recently, Breneman et al. (2011) reported observations of large amplitude lightning and transmitter whistler mode waves from two STEREO passes through the inner radiation belt (L 
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 5
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    Observations of a high-latitude stable electron auroral emission at ∼16 MLT during a large substorm (2011)
    Wiley
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    Publication Date: 2011-07-19
    Description: During an interval when the interplanetary magnetic field was large and primarily duskward and southward, a stable region of auroral emission was observed on 17 August 2001 by IMAGE at ∼16 magnetic local time, poleward of the main aurora, for 1 h, from before the onset of a large substorm through the recovery phase. In a region where ions showed the energy dispersion expected for the cusp, strong field-aligned currents and Poynting flux were observed by Polar (at 1.8 RE in the Southern Hemisphere) as it transited field lines mapping to the auroral spot in the Northern Hemisphere. The data are consistent with the hypothesis that the long-lasting electron auroral spot maps to the magnetopause region where reconnection was occurring. Under the assumption of conjugacy between the Northern and Southern hemispheres on these field lines, the Polar data suggest that the electrons on these field lines were accelerated by Alfvén waves and/or a quasi-static electric field, primarily at altitudes below a few RE since the in situ Poynting flux (mapped to 100 km) is comparable to the energy flux of the emission while the mapped in situ electron energy flux is much smaller. This event provides the first example of an emission due to electrons accelerated at low altitudes at the foot point of a region of quasi-steady dayside reconnection. Cluster data in the magnetotail indicate that the Poynting flux from the reconnection region during this substorm is large enough to account for the observed nightside aurora.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 6
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    Statistical distribution of whistler‐mode waves in the radiation belts with large magnetic field amplitudes and comparison to large electric field amplitudes (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract 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 MLT of 0‐14 where they are present approximately 1‐6% of the time. During high geomagnetic activity, high‐amplitude whistler‐mode wave occurrence rises above 25% in some regions. The day‐side population are more common during quiet or moderate geomagnetic activity and occur primarily 〉 5 degrees from the magnetic equator, while the night‐to‐dawn population are enhanced during active times and are primarily within 5 degrees 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 non‐linearly 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 100x the average wave amplitude.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
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  • 7
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    Spatial Localization and Ducting of EMIC Waves: Van Allen Probes and Ground-based Observations (2014)
    Wiley
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    Publication Date: 2014-01-17
    Description: [1]  On 11 th October 2012, during the recovery phase of a moderate geomagnetic storm, an extended interval (〉 18 hours) of continuous EMIC waves was observed by CARISMA and STEP induction coil magnetometers in North America. At around 14:15 UT, both Van Allen Probes B and A (65 degrees magnetic longitude apart) in conjunction with the ground array observed very narrow (ΔL ~ 0.1-0.4) left-hand polarized EMIC emission confined to regions of mass density gradients at the outer edge of the plasmasphere at L ~ 4. EMIC waves were seen with complex polarization patterns on the ground, in good agreement with model results from Woodroffe and Lysak [2012] and consistent with Earth's rotation sweeping magnetometer stations across multiple polarization reversals in the fields in the Earth-ionosphere duct. The narrow L-widths explain the relative rarity of space-based EMIC occurrence, ground-based measurements providing better estimates of global EMIC wave occurrence for input into radiation belt dynamical models.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 8
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    Megavolt Parallel Potentials Arising from Double-Layer Streams in the Earth’s Outer Radiation Belt (2013)
    American Physical Society (APS)
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    Publication Date: 2013-12-03
    Description: Author(s): F. S. Mozer, S. D. Bale, J. W. Bonnell, C. C. Chaston, I. Roth, and J. Wygant Huge numbers of double layers carrying electric fields parallel to the local magnetic field line have been observed on the Van Allen probes in connection with in situ relativistic electron acceleration in the Earth’s outer radiation belt. For one case with adequate high time resolution data, 7000 do... [Phys. Rev. Lett. 111, 235002] Published Mon Dec 02, 2013
    Keywords: Plasma and Beam Physics
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society (APS)
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  • 9
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    Evolution of relativistic outer belt electrons during an extended quiescent period (2014)
    Wiley
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    Publication Date: 2014-10-21
    Description: To effectively study steady loss due to hiss-driven precipitation of relativistic electrons in the outer radiation belt, it is useful to isolate this loss by studying a time of relatively quiet geomagnetic activity. We present a case of initial enhancement and slow, steady decay of 700 keV - 2 MeV electron populations in the outer radiation belt during an extended quiescent period from ~15 December 2012 - 13 January 2013. We incorporate particle measurements from a constellation of satellites, including the Colorado Student Space Weather Experiment (CSSWE) CubeSat, the Van Allen Probes twin spacecraft, and THEMIS, to understand the evolution of the electron populations across pitch angle and energy. Additional data from calculated phase space density (PSD), as well as hiss and chorus wave data from Van Allen Probes, helps complete the picture of the slow precipitation loss of relativistic electrons during a quiet time. Electron loss to the atmosphere during this event is quantified through use of the Loss Index Method, utilizing CSSWE measurements at LEO. By comparing these results against equatorial Van Allen Probes electron flux data, we conclude the net precipitation loss of the outer radiation belt content to be greater than 92%, suggesting no significant acceleration during this period, and resulting in faster electron loss rates than have previously been reported.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 10
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    A Statistical Study of EMIC Waves Associated With and Without Energetic Particle Injection From the Magnetotail (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract To understand the relationship between generation of electromagnetic ion cyclotron (EMIC) waves and energetic particle injections, we performed a statistical study of EMIC waves associated with and without injections based on the Van Allen Probes (Radiation Belt Storm Probes) and Geostationary Operational Environmental Satellite (GOES; GOES‐13 and GOES‐15) observations. Using 47 months of observations, we identified wave events seen by the Van Allen Probes relative to the plasmapause and to energetic particle injections seen by GOES‐13 and GOES‐15 on the nightside. We separated the events into four categories: EMIC waves with (without) injections inside (outside) the plasmasphere. We found that He+ EMIC waves have higher occurrence rate inside the plasmasphere, while H+ EMIC waves predominantly occur outside the plasmasphere. Meanwhile, the time duration and peak occurrence rate of EMIC waves associated with injections are shorter and limited to a narrower magnetic local time region than those without injections, indicating that these waves have localized source regions. He+ EMIC waves inside the plasmasphere associated with injection are usually accompanied by an increase in H+ flux within energies of 1–50 keV through all magnetic local time regions, while most wave events outside the plasmasphere show less relationship with H+ flux increase. From these observations, we suggest that injected hot ions are the major driver of He+ EMIC waves inside the plasmasphere during active time. Expanding plasmasphere during quiet times can provide broad wave source regions for He+ EMIC waves on the dayside. However, H+ EMIC waves outside the plasmasphere show different characteristics, suggesting that these waves are generated by other processes.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
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