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Found 584 entries in the Bibliography.
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| 2015 |
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We perform a statistical study of electromagnetic ion cyclotron (EMIC) waves detected by the Van Allen Probes mission to investigate the spatial distribution of their occurrence, wave power, ellipticity, and normal angle. The Van Allen Probes have been used which allow us to explore the inner magnetosphere (1.1 to 5.8 Re). Magnetic field measurements from the Electric and Magnetic Field Instrument Suite and Integrated Science onboard the Van Allen Probes are used to identify EMIC wave events for the first 22 months of the mission operation (8 September 2012 \textendash 30 June 2014). EMIC waves are examined in H+-, He+-, and O+-bands. Over 700 EMIC wave events have been identified over the three different wave bands (265 H+-band events, 438 He+-band events, and 68 O+-band events). EMIC wave events are observed between L = 2 \textendash 8, with over 140 EMIC wave events observed below L = 4. Results show that H+-band EMIC waves have two peak MLT occurrence regions: pre-noon (0900 < MLT <= 1200) and afternoon (1500 < MLT <= 1700) sectors. He+-band EMIC waves feature an overall stronger dayside occurrence. O+-band EMIC waves have one peak region located in the morning sector at lower L-shells (L < 4). He+-band EMIC waves average the highest wave power overall (>0.1 nT2/Hz), especially in the afternoon sector. Ellipticity observations reveal that linearly polarized EMIC wave dominate in lower L-shells. Saikin, A.; Zhang, J.-C.; Allen, R.C.; Smith, C.; Kistler, L.; Spence, H.; Torbert, R.; Kletzing, C.; Jordanova, V.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2015 YEAR: 2015 DOI: 10.1002/2015JA021358 EMIC waves; Fast Fourier Transform; spatial distribution; Van Allen Probes |
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We perform a statistical study of electromagnetic ion cyclotron (EMIC) waves detected by the Van Allen Probes mission to investigate the spatial distribution of their occurrence, wave power, ellipticity, and normal angle. The Van Allen Probes have been used which allow us to explore the inner magnetosphere (1.1 to 5.8 Re). Magnetic field measurements from the Electric and Magnetic Field Instrument Suite and Integrated Science onboard the Van Allen Probes are used to identify EMIC wave events for the first 22 months of the mission operation (8 September 2012 \textendash 30 June 2014). EMIC waves are examined in H+-, He+-, and O+-bands. Over 700 EMIC wave events have been identified over the three different wave bands (265 H+-band events, 438 He+-band events, and 68 O+-band events). EMIC wave events are observed between L = 2 \textendash 8, with over 140 EMIC wave events observed below L = 4. Results show that H+-band EMIC waves have two peak MLT occurrence regions: pre-noon (0900 < MLT <= 1200) and afternoon (1500 < MLT <= 1700) sectors. He+-band EMIC waves feature an overall stronger dayside occurrence. O+-band EMIC waves have one peak region located in the morning sector at lower L-shells (L < 4). He+-band EMIC waves average the highest wave power overall (>0.1 nT2/Hz), especially in the afternoon sector. Ellipticity observations reveal that linearly polarized EMIC wave dominate in lower L-shells. Saikin, A.; Zhang, J.-C.; Allen, R.C.; Smith, C.; Kistler, L.; Spence, H.; Torbert, R.; Kletzing, C.; Jordanova, V.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2015 YEAR: 2015 DOI: 10.1002/2015JA021358 EMIC waves; Fast Fourier Transform; spatial distribution; Van Allen Probes |
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During early November 2013, the magnetosphere experienced concurrent driving by a coronal mass ejection (CME) during an ongoing high-speed stream (HSS) event. The relativistic electron response to these two kinds of drivers, i.e., HSS and CME, is typically different, with the former often leading to a slower buildup of electrons at larger radial distances, while the latter energizing electrons rapidly with flux enhancements occurring closer to the Earth.We present a detailed analysis of the relativistic electron response including radial profiles of phase space density as observed by both MagEIS and REPT instruments on the Van Allen Probes mission. Data from the MagEIS instrument establishes the behavior of lower energy (<1MeV) electrons which span both intermediary and seed populations during electron energization. Measurements characterizing the plasma waves and magnetospheric electric and magnetic fields during this period are obtained by the EMFISIS instrument on board Van Allen Probes, SCM and FGM instruments onboard THEMIS, and the low altitude polar orbiting POES satellite. These observations suggest that, during this time period, both radial transport and local in-situ processes are involved in the energization of electrons. The energization attributable to radial diffusion is most clearly evident for the lower energy (<1MeV) electrons, while the effects of in-situ energization by interaction of chorus waves are prominent in the higher energy electrons. Kanekal, S.; Baker, D.; Henderson, M.; Li, W.; Fennell, J.; Zheng, Y.; Richardson, I.; Jones, A.; Ali, A.; Elkington, S.; Jaynes, A.; Li, X.; Blake, J.; Reeves, G.; Spence, H.; Kletzing, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2015 YEAR: 2015 DOI: 10.1002/2015JA021395 CME; HSS; Van Allen Probes; IP shock; relativistic electrons |
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We show the first evidence for locally excited chorus at frequencies below 0.1 fce (electron cyclotron frequency) in the outer radiation belt. A statistical study of chorus during geomagnetic storms observed by the Van Allen Probes found that frequencies are often dramatically lower than expected. The frequency at peak power suddenly stops tracking the equatorial 0.5 fce and f/fce decreases rapidly, often to frequencies well below 0.1 fce (in situ and mapped to equator). These very low frequency waves are observed both when the satellites are close to the equatorial plane and at higher magnetic latitudes. Poynting flux is consistent with generation at the equator. Wave amplitudes can be up to 20 to 40 mV/m and 2 to 4 nT. We conclude that conditions during moderate to large storms can excite unusually low frequency chorus, which is resonant with more energetic electrons than typical chorus, with critical implications for understanding radiation belt evolution. Cattell, C.; Breneman, A.; Thaller, S.; Wygant, J.; Kletzing, C.; Kurth, W.; Published by: Geophysical Research Letters Published on: 09/2015 YEAR: 2015 DOI: 10.1002/2015GL065565 |
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We show the first evidence for locally excited chorus at frequencies below 0.1 fce (electron cyclotron frequency) in the outer radiation belt. A statistical study of chorus during geomagnetic storms observed by the Van Allen Probes found that frequencies are often dramatically lower than expected. The frequency at peak power suddenly stops tracking the equatorial 0.5 fce and f/fce decreases rapidly, often to frequencies well below 0.1 fce (in situ and mapped to equator). These very low frequency waves are observed both when the satellites are close to the equatorial plane and at higher magnetic latitudes. Poynting flux is consistent with generation at the equator. Wave amplitudes can be up to 20 to 40 mV/m and 2 to 4 nT. We conclude that conditions during moderate to large storms can excite unusually low frequency chorus, which is resonant with more energetic electrons than typical chorus, with critical implications for understanding radiation belt evolution. Cattell, C.; Breneman, A.; Thaller, S.; Wygant, J.; Kletzing, C.; Kurth, W.; Published by: Geophysical Research Letters Published on: 09/2015 YEAR: 2015 DOI: 10.1002/2015GL065565 |
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Broadband low frequency electromagnetic waves in the inner magnetosphere A prominent yet largely unrecognized feature of the inner magnetosphere associated with particle injections, and more generally geomagnetic storms, is the occurrence of broadband electromagnetic field fluctuations over spacecraft frame frequencies (fsc) extending from effectively zero to fsc ≳ 100 Hz. Using observations from the Van Allen Probes we show that these waves most commonly occur pre-midnight but are observed over a range of local times extending into the dayside magnetosphere. We find that the variation of magnetic spectral energy density with fsc obeys inline image over several decades with a spectral break-point at fb ≈1 Hz. The values for α are log normally distributed with α = 1.9 \textpm 0.6 for fsc < fb andα = 2.9 \textpm 0.6 for fsc > fb. A is a function of geomagnetic activity with the largest values observed over intervals of decreasing Dst index during the main phase of geomagnetic storms. At these times these waves are nearly always present in the night-side inner magnetosphere and are commonly observed from L = 3 outward. The observed variation of the electric to magnetic field amplitude with fsc is well described by a dispersive Alfv\ en wave model under the assumption that fsc is primarily a consequence of the Doppler shift of plasma frame structures moving over the spacecraft. The robust anti-correlation between the time rate change of the Dst index and wave spectral energy density coupled with the ability of dispersive Alfv\ en waves to drive transverse ion acceleration suggests that these waves may boost ion energy density in the inner magnetosphere and intensify the ring current during storm times. Chaston, C.; Bonnell, J.; Kletzing, C.; Hospodarsky, G.; Wygant, J.; Smith, C.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2015 YEAR: 2015 DOI: 10.1002/2015JA021690 Alfven waves; Geomagnetic storms; ring current; turbulence; Van Allen Probes |
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This study is focused on understanding the coupling between different electron populations in the inner magnetosphere and the various physical processes that determine evolution of electron fluxes at different energies. Observations during the March 17, 2013 storm and simulations with a newly developed Versatile Electron Radiation Belt-4D (VERB-4D) are presented. Analysis of the drift trajectories of the energetic and relativistic electrons shows that electron trajectories at transitional energies with a first invariant on the scale of ~100MeV/G may resemble ring current or relativistic electron trajectories depending on the level of geomagnetic activity. Simulations with the VERB-4D code including convection, radial diffusion, and energy diffusion are presented. Sensitivity simulations including various physical processes show how different acceleration mechanisms contribute to the energization of energetic electrons at transitional energies. In particular, the range of energies where inward transport is strongly influenced by both convection and radial diffusion are studied. The results of the 4D simulations are compared to Van Allen Probes observations at a range of energies including source, seed, and core populations of the energetic and relativistic electrons in the inner magnetosphere. Shprits, Yuri; Kellerman, Adam; Drozdov, Alexander; Spense, Harlan; Reeves, Geoffrey; Baker, Daniel; Published by: Geophysical Research Letters Published on: 09/2015 YEAR: 2015 DOI: 10.1002/2015GL065230 inner magnetosphere; numerical simulations; Radiation belts; ring current; Van Allen Probes; wave-particle interactions |
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We report on simultaneous spacecraft and ground-based observations of quasiperiodic VLF emissions and related energetic-electron dynamics. Quasiperiodic emissions in the frequency range 2\textendash6 kHz were observed during a substorm on 25 January 2013 by Van Allen Probe-A and a ground-based station in the Northern Finland. The spacecraft detected the VLF signals near the geomagnetic equator in the night sector at L = 3.0\textendash4.2 when it was inside the plasmasphere. During the satellite motion toward higher latitudes, the time interval between quasiperiodic elements decreased from 6 min to 3 min. We find one-to-one correspondence between the quasiperiodic elements detected by Van Allen Probe-A and on the ground, which indicates the temporal nature of the observed variation in the time interval between quasiperiodic elements. Multiсomponent measurements of the wave electric and magnetic fields by the Van Allen Probe-A show that the quasiperiodic emissions were almost circularly right-hand polarized whistler mode waves and had predominantly small (below 30\textdegree) wave vector angles with respect to the magnetic field. In the probable source region of these signals (L about 4), we observed synchronous variations of electron distribution function at energies of 10\textendash20 keV and the quasiperiodic elements. In the pause between the quasiperiodic elements pitch angle distribution of these electrons had a maximum near 90\textdegree, while they become more isotropic during the development of quasiperiodic elements. The parallel energies of the electrons for which the data suggest direct evidence of the wave-particle interactions is in a reasonable agreement with the estimated cyclotron resonance energy for the observed waves. Titova, E.; Kozelov, B.; Demekhov, A.; Manninen, J.; Santolik, O.; Kletzing, C.; Reeves, G.; Published by: Geophysical Research Letters Published on: 08/2015 YEAR: 2015 DOI: 10.1002/grl.v42.1510.1002/2015GL064911 energetic electrons; quasiperiodic emissions; Van Allen Probes; VLF waves |
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Low-harmonic magnetosonic waves observed by the Van Allen Probes Purely compressional electromagnetic waves (fast magnetosonic waves), generated at multiple harmonics of the local proton gyrofrequency, have been observed by various types of satellite instruments (fluxgate and search coil magnetometers and electric field sensors), but most recent studies have used data from search coil sensors, and many have been restricted to high harmonics. We report here on a survey of low-harmonic waves, based on electric and magnetic field data from the EFW double probe and EMFISIS fluxgate magnetometer instruments, respectively, on the Van Allen Probes spacecraft during its first full precession through all local times, from October 1, 2012 through July 13, 2014. These waves were observed both inside and outside the plasmapause (PP), at L shells from 2.4 to ~6 (the spacecraft apogee), and in regions with plasma number densities ranging from 10 to >1000 cm-3. Consistent with earlier studies, wave occurrence was sharply peaked near the magnetic equator. Waves appeared at all local times but were more common from noon to dusk, and often occurred within three hours after substorm injections. Outside the PP occurrence maximized broadly across noon, and inside the PP occurrence maximized in the dusk sector, in an extended plasmasphere. We confirm recent ray-tracing studies showing wave refraction and/or reflection at PP-like boundaries. Comparison with waveform receiver data indicates that in some cases these low-harmonic magnetosonic wave events occurred independently of higher-harmonic waves; this indicates the importance of including this population in future studies of radiation belt dynamics. Posch, J.; Engebretson, M.; Olson, C.; Thaller, S.; Breneman, A.; Wygant, J.; Boardsen, S.; Kletzing, C.; Smith, C.; Reeves, G.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2015 YEAR: 2015 DOI: 10.1002/2015JA021179 equatorial noise; inner magnetosphere; magnetosonic waves; Van Allen Probes; waves in plasmas |
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Low-harmonic magnetosonic waves observed by the Van Allen Probes Purely compressional electromagnetic waves (fast magnetosonic waves), generated at multiple harmonics of the local proton gyrofrequency, have been observed by various types of satellite instruments (fluxgate and search coil magnetometers and electric field sensors), but most recent studies have used data from search coil sensors, and many have been restricted to high harmonics. We report here on a survey of low-harmonic waves, based on electric and magnetic field data from the EFW double probe and EMFISIS fluxgate magnetometer instruments, respectively, on the Van Allen Probes spacecraft during its first full precession through all local times, from October 1, 2012 through July 13, 2014. These waves were observed both inside and outside the plasmapause (PP), at L shells from 2.4 to ~6 (the spacecraft apogee), and in regions with plasma number densities ranging from 10 to >1000 cm-3. Consistent with earlier studies, wave occurrence was sharply peaked near the magnetic equator. Waves appeared at all local times but were more common from noon to dusk, and often occurred within three hours after substorm injections. Outside the PP occurrence maximized broadly across noon, and inside the PP occurrence maximized in the dusk sector, in an extended plasmasphere. We confirm recent ray-tracing studies showing wave refraction and/or reflection at PP-like boundaries. Comparison with waveform receiver data indicates that in some cases these low-harmonic magnetosonic wave events occurred independently of higher-harmonic waves; this indicates the importance of including this population in future studies of radiation belt dynamics. Posch, J.; Engebretson, M.; Olson, C.; Thaller, S.; Breneman, A.; Wygant, J.; Boardsen, S.; Kletzing, C.; Smith, C.; Reeves, G.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2015 YEAR: 2015 DOI: 10.1002/2015JA021179 equatorial noise; inner magnetosphere; magnetosonic waves; Van Allen Probes; waves in plasmas |
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Substorms generally inject 10s-100s keV electrons, but intense substorm electric fields have been shown to inject MeV electrons as well. An intriguing question is whether such MeV electron injections can populate the outer radiation belt. Here we present observations of a substorm injection of MeV electrons into the inner magnetosphere. In the pre-midnight sector at L\~5.5, Van Allen Probes (RBSP)-A observed a large dipolarization electric field (50mV/m) over \~40s and a dispersionless injection of electrons up to \~3 MeV. Pitch angle observations indicated betatron acceleration of MeV electrons at the dipolarization front. Corresponding signals of MeV electron injection were observed at LANL-GEO, THEMIS-D, and GOES at geosynchronous altitude. Through a series of dipolarizations, the injections increased the MeV electron phase space density by one order of magnitude in less than 3 hours in the outer radiation belt (L>4.8). Our observations provide evidence that deep injections can supply significant MeV electrons. Dai, Lei; Wang, Chi; Duan, Suping; He, Zhaohai; Wygant, John; Cattell, Cynthia; Tao, Xin; Su, Zhenpeng; Kletzing, Craig; Baker, Daniel; Li, Xinlin; Malaspina, David; Blake, Bernard; Fennell, Joseph; Claudepierre, Seth; Turner, Drew; Reeves, Geoffrey; Funsten, Herbert; Spence, Harlan; Angelopoulos, Vassilis; Fruehauff, Dennis; Chen, Lunjin; Thaller, Scott; Breneman, Aaron; Tang, Xiangwei; Published by: Geophysical Research Letters Published on: 07/2015 YEAR: 2015 DOI: 10.1002/2015GL064955 electric fields; radiation belt electrons; substorm dipolarization; substorm injection; Van Allen Probes |
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Substorms generally inject 10s-100s keV electrons, but intense substorm electric fields have been shown to inject MeV electrons as well. An intriguing question is whether such MeV electron injections can populate the outer radiation belt. Here we present observations of a substorm injection of MeV electrons into the inner magnetosphere. In the pre-midnight sector at L\~5.5, Van Allen Probes (RBSP)-A observed a large dipolarization electric field (50mV/m) over \~40s and a dispersionless injection of electrons up to \~3 MeV. Pitch angle observations indicated betatron acceleration of MeV electrons at the dipolarization front. Corresponding signals of MeV electron injection were observed at LANL-GEO, THEMIS-D, and GOES at geosynchronous altitude. Through a series of dipolarizations, the injections increased the MeV electron phase space density by one order of magnitude in less than 3 hours in the outer radiation belt (L>4.8). Our observations provide evidence that deep injections can supply significant MeV electrons. Dai, Lei; Wang, Chi; Duan, Suping; He, Zhaohai; Wygant, John; Cattell, Cynthia; Tao, Xin; Su, Zhenpeng; Kletzing, Craig; Baker, Daniel; Li, Xinlin; Malaspina, David; Blake, Bernard; Fennell, Joseph; Claudepierre, Seth; Turner, Drew; Reeves, Geoffrey; Funsten, Herbert; Spence, Harlan; Angelopoulos, Vassilis; Fruehauff, Dennis; Chen, Lunjin; Thaller, Scott; Breneman, Aaron; Tang, Xiangwei; Published by: Geophysical Research Letters Published on: 07/2015 YEAR: 2015 DOI: 10.1002/2015GL064955 electric fields; radiation belt electrons; substorm dipolarization; substorm injection; Van Allen Probes |
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Source and Seed Populations for Relativistic Electrons: Their Roles in Radiation Belt Changes Strong enhancements of outer Van Allen belt electrons have been shown to have a clear dependence on solar wind speed and on the duration of southward interplanetary magnetic field. However, individual case study analyses also have demonstrated that many geomagnetic storms produce little in the way of outer belt enhancements and, in fact, may produce substantial losses of relativistic electrons. In this study, focused upon a key period in August-September 2014, we use GOES geostationary orbit electron flux data and Van Allen Probes particle and fields data to study the process of radiation belt electron acceleration. One particular interval, 13-22 September, initiated by a short-lived geomagnetic storm and characterized by a long period of primarily northward IMF, showed strong depletion of relativistic electrons (including an unprecedented observation of long-lasting depletion at geostationary orbit) while an immediately preceding, and another immediately subsequent, storm showed strong radiation belt enhancement. We demonstrate with these data that two distinct electron populations resulting from magnetospheric substorm activity are crucial elements in the ultimate acceleration of highly relativistic electrons in the outer belt: the source population (tens of keV) that give rise to VLF wave growth; and the seed population (hundreds of keV) that are, in turn, accelerated through VLF wave interactions to much higher energies. ULF waves may also play a role by either inhibiting or enhancing this process through radial diffusion effects. If any components of the inner magnetospheric accelerator happen to be absent, the relativistic radiation belt enhancement fails to materialize. Jaynes, A.N.; Baker, D.N.; Singer, H.J.; Rodriguez, J.V.; Loto\textquoterightaniu, T.M.; Ali, A.; Elkington, S.R.; Li, X.; Kanekal, S.G.; Fennell, J.F.; Li, W.; Thorne, R.M.; Kletzing, C.A.; Spence, H.E.; Reeves, G.D.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2015 YEAR: 2015 DOI: 10.1002/2015JA021234 Radiation belts; relativistic electrons; substorms; ULF waves; Van Allen Probes; VLF waves |
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We report correlated data on nightside chorus waves and energetic electrons during two small storm periods: 1 November 2012 (Dst≈-45) and 14 January 2013 (Dst≈-18). The Van Allen Probes simultaneously observed strong chorus waves at locations L = 5.8 - 6.3, with a lower frequency band 0.1 - 0.5fce and a peak spectral density \~[10-4 nT2/Hz. In the same period, the fluxes and anisotropy of energetic (\~ 10-300 keV) electrons were greatly enhanced in the interval of large negative interplanetary magnetic field Bz. Using a bi-Maxwellian distribution to model the observed electron distribution, we perform ray tracing simulations to show that nightside chorus waves are indeed produced by the observed electron distribution with a peak growth for a field-aligned propagation around between 0.3fce and 0.4fce, at latitude <7o. Moreover, chorus waves launched with initial normal angles either θ < 90o or >90o propagate along the field either northward or southward, and then bounce back either away from Earth for a lower frequency or towards Earth for higher frequencies. The current results indicate that nightside chorus waves can be excited even during weak geomagnetic activities in cases of continuous injection associated with negative Bz. Moreover, we examine a dayside event during a small storm C on 8 May 2014 (Dst≈-45) and find that the observed anisotropic energetic electron distributions potentially contribute to the generation of dayside chorus waves, but this requires more thorough studies in the future. He, Yihua; Xiao, Fuliang; Zhou, Qinghua; Yang, Chang; Liu, Si; Baker, D.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Reeves, G.; Funsten, H.; Blake, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2015 YEAR: 2015 DOI: 10.1002/2015JA021376 chorus wave excitation; energetic electrons; Geomagnetic storm; Van Allen Probes; Van Allen probes results; Wave-particle interaction |
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Theory and observations have linked equatorial VLF waves with pulsating aurora for decades, invoking the process of pitch-angle scattering of 10\textquoterights keV electrons in the equatorial magnetosphere. Recently published satellite studies have strengthened this argument, by showing strong correlation between pulsating auroral patches and both lower-band chorus and 10\textquoterights keV electron modulation in the vicinity of geosynchronous orbit. Additionally, a previous link has been made between Pc4-5 compressional pulsations and modulation of whistler-mode chorus using THEMIS. In the current study, we present simultaneous in-situ observations of structured chorus waves and an apparent field line resonance (in the Pc4-5 range) as a result of a substorm injection, observed by Van Allen Probes, along with ground-based observations of pulsating aurora. We demonstrate the likely scenario being one of substorm-driven Pc4-5 ULF pulsations modulating chorus waves, and thus providing the driver for pulsating particle precipitation into the Earth\textquoterights atmosphere. Interestingly, the modulated chorus wave and ULF wave periods are well correlated, with chorus occurring at half the periodicity of the ULF waves. We also show, for the first time, a particular few-Hz modulation of individual chorus elements that coincides with the same modulation in a nearby pulsating aurora patch. Such modulation has been noticed as a high-frequency component in ground-based camera data of pulsating aurora for decades, and may be a result of nonlinear chorus wave interactions in the equatorial region. Jaynes, A.; Lessard, M.; Takahashi, K.; Ali, A.; Malaspina, D.; Michell, R.; Spanswick, E.; Baker, D.; Blake, J.; Cully, C.; Donovan, E.; Kletzing, C.; Reeves, G.; Samara, M.; Spence, H.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2015 YEAR: 2015 DOI: 10.1002/2015JA021380 aurora; precipitation; pulsating aurora; substorms; ULF waves; Van Allen Probes; VLF waves |
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Theory and observations have linked equatorial VLF waves with pulsating aurora for decades, invoking the process of pitch-angle scattering of 10\textquoterights keV electrons in the equatorial magnetosphere. Recently published satellite studies have strengthened this argument, by showing strong correlation between pulsating auroral patches and both lower-band chorus and 10\textquoterights keV electron modulation in the vicinity of geosynchronous orbit. Additionally, a previous link has been made between Pc4-5 compressional pulsations and modulation of whistler-mode chorus using THEMIS. In the current study, we present simultaneous in-situ observations of structured chorus waves and an apparent field line resonance (in the Pc4-5 range) as a result of a substorm injection, observed by Van Allen Probes, along with ground-based observations of pulsating aurora. We demonstrate the likely scenario being one of substorm-driven Pc4-5 ULF pulsations modulating chorus waves, and thus providing the driver for pulsating particle precipitation into the Earth\textquoterights atmosphere. Interestingly, the modulated chorus wave and ULF wave periods are well correlated, with chorus occurring at half the periodicity of the ULF waves. We also show, for the first time, a particular few-Hz modulation of individual chorus elements that coincides with the same modulation in a nearby pulsating aurora patch. Such modulation has been noticed as a high-frequency component in ground-based camera data of pulsating aurora for decades, and may be a result of nonlinear chorus wave interactions in the equatorial region. Jaynes, A.; Lessard, M.; Takahashi, K.; Ali, A.; Malaspina, D.; Michell, R.; Spanswick, E.; Baker, D.; Blake, J.; Cully, C.; Donovan, E.; Kletzing, C.; Reeves, G.; Samara, M.; Spence, H.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2015 YEAR: 2015 DOI: 10.1002/2015JA021380 aurora; precipitation; pulsating aurora; substorms; ULF waves; Van Allen Probes; VLF waves |
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Global-scale coherence modulation of radiation-belt electron loss from plasmaspheric hiss Over 40 years ago it was suggested that electron loss in the region of the radiation belts that overlaps with the region of high plasma density called the plasmasphere, within four to five Earth radii1, 2, arises largely from interaction with an electromagnetic plasma wave called plasmaspheric hiss3, 4, 5. This interaction strongly influences the evolution of the radiation belts during a geomagnetic storm, and over the course of many hours to days helps to return the radiation-belt structure to its \textquoteleftquiet\textquoteright pre-storm configuration. Observations have shown that the long-term electron-loss rate is consistent with this theory but the temporal and spatial dynamics of the loss process remain to be directly verified. Here we report simultaneous measurements of structured radiation-belt electron losses and the hiss phenomenon that causes the losses. Losses were observed in the form of bremsstrahlung X-rays generated by hiss-scattered electrons colliding with the Earth\textquoterights atmosphere after removal from the radiation belts. Our results show that changes of up to an order of magnitude in the dynamics of electron loss arising from hiss occur on timescales as short as one to twenty minutes, in association with modulations in plasma density and magnetic field. Furthermore, these loss dynamics are coherent with hiss dynamics on spatial scales comparable to the size of the plasmasphere. This nearly global-scale coherence was not predicted and may affect the short-term evolution of the radiation belts during active times. Breneman, A.; Halford, A.; Millan, R.; McCarthy, M.; Fennell, J.; Sample, J.; Woodger, L.; Hospodarsky, G.; Wygant, J.; Cattell, C.; Goldstein, J.; Malaspina, D.; Kletzing, C.; Published by: Nature Published on: 06/2015 YEAR: 2015 DOI: 10.1038/nature14515 |
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Global-scale coherence modulation of radiation-belt electron loss from plasmaspheric hiss Over 40 years ago it was suggested that electron loss in the region of the radiation belts that overlaps with the region of high plasma density called the plasmasphere, within four to five Earth radii1, 2, arises largely from interaction with an electromagnetic plasma wave called plasmaspheric hiss3, 4, 5. This interaction strongly influences the evolution of the radiation belts during a geomagnetic storm, and over the course of many hours to days helps to return the radiation-belt structure to its \textquoteleftquiet\textquoteright pre-storm configuration. Observations have shown that the long-term electron-loss rate is consistent with this theory but the temporal and spatial dynamics of the loss process remain to be directly verified. Here we report simultaneous measurements of structured radiation-belt electron losses and the hiss phenomenon that causes the losses. Losses were observed in the form of bremsstrahlung X-rays generated by hiss-scattered electrons colliding with the Earth\textquoterights atmosphere after removal from the radiation belts. Our results show that changes of up to an order of magnitude in the dynamics of electron loss arising from hiss occur on timescales as short as one to twenty minutes, in association with modulations in plasma density and magnetic field. Furthermore, these loss dynamics are coherent with hiss dynamics on spatial scales comparable to the size of the plasmasphere. This nearly global-scale coherence was not predicted and may affect the short-term evolution of the radiation belts during active times. Breneman, A.; Halford, A.; Millan, R.; McCarthy, M.; Fennell, J.; Sample, J.; Woodger, L.; Hospodarsky, G.; Wygant, J.; Cattell, C.; Goldstein, J.; Malaspina, D.; Kletzing, C.; Published by: Nature Published on: 06/2015 YEAR: 2015 DOI: 10.1038/nature14515 |
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A statistical study of EMIC waves observed by Cluster: 1. Wave properties Electromagnetic ion cyclotron (EMIC) waves are an important mechanism for particle energization and losses inside the magnetosphere. In order to better understand the effects of these waves on particle dynamics, detailed information about the occurrence rate, wave power, ellipticity, normal angle, energy propagation angle distributions, as well as local plasma parameters are required. Previous statistical studies have used in situ observations to investigate the distribution of these parameters in the MLT-L frame within a limited MLAT range. In this study, we present a statistical analysis of EMIC wave properties using ten years (2001\textendash2010) of data from Cluster, totaling 25,431 minutes of wave activity. Due to the polar orbit of Cluster, we are able to investigate EMIC waves at all MLATs and MLTs. This allows us to further investigate the MLAT dependence of various wave properties inside different MLT sectors and further explore the effects of Shabansky orbits on EMIC wave generation and propagation. The statistical analysis is presented in two papers. This paper focuses on the wave occurrence distribution as well as the distribution of wave properties. The companion paper focuses on local plasma parameters during wave observations as well as wave generation proxies. Allen, R.; Zhang, J.; Kistler, L.; Spence, H.; Lin, R.; Klecker, B.; Dunlop, M.; e, Andr\; Jordanova, V.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2015 YEAR: 2015 DOI: 10.1002/2015JA021333 |
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A statistical study of EMIC waves observed by Cluster: 1. Wave properties Electromagnetic ion cyclotron (EMIC) waves are an important mechanism for particle energization and losses inside the magnetosphere. In order to better understand the effects of these waves on particle dynamics, detailed information about the occurrence rate, wave power, ellipticity, normal angle, energy propagation angle distributions, as well as local plasma parameters are required. Previous statistical studies have used in situ observations to investigate the distribution of these parameters in the MLT-L frame within a limited MLAT range. In this study, we present a statistical analysis of EMIC wave properties using ten years (2001\textendash2010) of data from Cluster, totaling 25,431 minutes of wave activity. Due to the polar orbit of Cluster, we are able to investigate EMIC waves at all MLATs and MLTs. This allows us to further investigate the MLAT dependence of various wave properties inside different MLT sectors and further explore the effects of Shabansky orbits on EMIC wave generation and propagation. The statistical analysis is presented in two papers. This paper focuses on the wave occurrence distribution as well as the distribution of wave properties. The companion paper focuses on local plasma parameters during wave observations as well as wave generation proxies. Allen, R.; Zhang, J.; Kistler, L.; Spence, H.; Lin, R.; Klecker, B.; Dunlop, M.; e, Andr\; Jordanova, V.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2015 YEAR: 2015 DOI: 10.1002/2015JA021333 |
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A statistical study of EMIC waves observed by Cluster: 1. Wave properties Electromagnetic ion cyclotron (EMIC) waves are an important mechanism for particle energization and losses inside the magnetosphere. In order to better understand the effects of these waves on particle dynamics, detailed information about the occurrence rate, wave power, ellipticity, normal angle, energy propagation angle distributions, as well as local plasma parameters are required. Previous statistical studies have used in situ observations to investigate the distribution of these parameters in the MLT-L frame within a limited MLAT range. In this study, we present a statistical analysis of EMIC wave properties using ten years (2001\textendash2010) of data from Cluster, totaling 25,431 minutes of wave activity. Due to the polar orbit of Cluster, we are able to investigate EMIC waves at all MLATs and MLTs. This allows us to further investigate the MLAT dependence of various wave properties inside different MLT sectors and further explore the effects of Shabansky orbits on EMIC wave generation and propagation. The statistical analysis is presented in two papers. This paper focuses on the wave occurrence distribution as well as the distribution of wave properties. The companion paper focuses on local plasma parameters during wave observations as well as wave generation proxies. Allen, R.; Zhang, J.; Kistler, L.; Spence, H.; Lin, R.; Klecker, B.; Dunlop, M.; e, Andr\; Jordanova, V.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2015 YEAR: 2015 DOI: 10.1002/2015JA021333 |
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Although most studies of the effects of EMIC waves on Earth\textquoterights outer radiation belt have focused on events in the afternoon sector in the outer plasmasphere or plume region, strong magnetospheric compressions provide an additional stimulus for EMIC wave generation across a large range of local times and L shells. We present here observations of the effects of a wave event on February 23, 2014 that extended over 8 hours in UT and over 12 hours in local time, stimulated by a gradual 4-hour rise and subsequent sharp increases in solar wind pressure. Large-amplitude linearly polarized hydrogen band EMIC waves (up to 25 nT p-p) appeared for over 4 hours at both Van Allen Probes, from late morning through local noon, when these spacecraft were outside the plasmapause, with densities ~5-20 cm-3. Waves were also observed by ground-based induction magnetometers in Antarctica (near dawn), Finland (near local noon), Russia (in the afternoon), and in Canada (from dusk to midnight). Ten passes of NOAA-POES and METOP satellites near the northern footpoint of the Van Allen Probes observed 30-80 keV subauroral proton precipitation, often over extended L shell ranges; other passes identified a narrow L-shell region of precipitation over Canada. Observations of relativistic electrons by the Van Allen Probes showed that the fluxes of more field-aligned and more energetic radiation belt electrons were reduced in response to both the emission over Canada and the more spatially extended emission associated with the compression, confirming the effectiveness of EMIC-induced loss processes for this event. Engebretson, M.; Posch, J.; Wygant, J.; Kletzing, C.; Lessard, M.; Huang, C.-L.; Spence, H.; Smith, C.; Singer, H.; Omura, Y.; Horne, R.; Reeves, G.; Baker, D.; Gkioulidou, M.; Oksavik, K.; Mann, I.; Raita, T; Shiokawa, K.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2015 YEAR: 2015 DOI: 10.1002/2015JA021227 EMIC waves; magnetospheric compressions; Radiation belts; Van Allen Probes |
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Although most studies of the effects of EMIC waves on Earth\textquoterights outer radiation belt have focused on events in the afternoon sector in the outer plasmasphere or plume region, strong magnetospheric compressions provide an additional stimulus for EMIC wave generation across a large range of local times and L shells. We present here observations of the effects of a wave event on February 23, 2014 that extended over 8 hours in UT and over 12 hours in local time, stimulated by a gradual 4-hour rise and subsequent sharp increases in solar wind pressure. Large-amplitude linearly polarized hydrogen band EMIC waves (up to 25 nT p-p) appeared for over 4 hours at both Van Allen Probes, from late morning through local noon, when these spacecraft were outside the plasmapause, with densities ~5-20 cm-3. Waves were also observed by ground-based induction magnetometers in Antarctica (near dawn), Finland (near local noon), Russia (in the afternoon), and in Canada (from dusk to midnight). Ten passes of NOAA-POES and METOP satellites near the northern footpoint of the Van Allen Probes observed 30-80 keV subauroral proton precipitation, often over extended L shell ranges; other passes identified a narrow L-shell region of precipitation over Canada. Observations of relativistic electrons by the Van Allen Probes showed that the fluxes of more field-aligned and more energetic radiation belt electrons were reduced in response to both the emission over Canada and the more spatially extended emission associated with the compression, confirming the effectiveness of EMIC-induced loss processes for this event. Engebretson, M.; Posch, J.; Wygant, J.; Kletzing, C.; Lessard, M.; Huang, C.-L.; Spence, H.; Smith, C.; Singer, H.; Omura, Y.; Horne, R.; Reeves, G.; Baker, D.; Gkioulidou, M.; Oksavik, K.; Mann, I.; Raita, T; Shiokawa, K.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2015 YEAR: 2015 DOI: 10.1002/2015JA021227 EMIC waves; magnetospheric compressions; Radiation belts; Van Allen Probes |
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A background correction algorithm for Van Allen Probes MagEIS electron flux measurements We describe an automated computer algorithm designed to remove background contamination from the Van Allen Probes MagEIS electron flux measurements. We provide a detailed description of the algorithm with illustrative examples from on-orbit data. We find two primary sources of background contamination in the MagEIS electron data: inner zone protons and bremsstrahlung X-rays generated by energetic electrons interacting with the spacecraft material. Bremsstrahlung X-rays primarily produce contamination in the lower energy MagEIS electron channels (~30-500 keV) and in regions of geospace where multi-MeV electrons are present. Inner zone protons produce contamination in all MagEIS energy channels at roughly L < 2.5. The background corrected MagEIS electron data produce a more accurate measurement of the electron radiation belts, as most earlier measurements suffer from unquantifiable and uncorrectable contamination in this harsh region of the near-Earth space environment. These background-corrected data will also be useful for spacecraft engineering purposes, providing ground truth for the near-Earth electron environment and informing the next generation of spacecraft design models (e.g., AE9). Claudepierre, S.; O\textquoterightBrien, T.; Blake, J.; Fennell, J.; Roeder, J.; Clemmons, J.; Looper, M.; Mazur, J.; Mulligan, T.; Spence, H.; Reeves, G.; Friedel, R.; Henderson, M.; Larsen, B.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2015 YEAR: 2015 DOI: 10.1002/2015JA021171 Background contamination; Inner radiation belt; outer radiation belt; Particle measurements; Radiation belt; Spacecraft engineering; Van Allen Probes |
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The twin Van Allen Probes spacecraft witnessed a series of lobe encounters between 0200 and 0515 UT on November 14th 2012. Although lobe entry had been observed previously by the other spacecraft, the two Van Allen Probe spacecraft allow us to observe the motion of the boundary for the first time. Moreover, this event is unique in that it consists of a series of six quasi-periodic lobe entries. The events occurred on the dawn flank between 4 and 6.6 local time and at altitudes between 5.6 and 6.2 RE. During the events Dst dropped to less than -100nT with the IMF being strongly southward (Bz = -15nT) and eastward (By = 20 nT). Observations by LANL GEO spacecraft at geosynchronous orbit also show lobe encounters in the northern hemisphere and on the dusk flank. The two spacecraft configuration provides strong evidence that these periodic entries into the lobe are the result of local expansions of the OCB propagating from the tail and passing over the Van Allen Probes. Examination of pitch angle binned data from the HOPE instrument shows spatially large, accelerated ion structures occurring near simultaneously at both spacecraft, with the presence of oxygen indicating that they have an ionospheric source. The outflows are dispersed in energy and are detected when the spacecraft are on both open and closed field lines. These events provide a chance to examine the global magnetic field topology in detail, as well as smaller scale spatial and temporal characteristics of the OCB, allowing us to constrain the position of the open/closed field line boundary and compare it to a global MHD model using a novel method. This technique shows that the model can reproduce a periodic approach and retreat of the OCB from the spacecraft but can overestimate its distance by as much as 3 RE. The model appears to simulate the dynamic processes that cause the spacecraft to encounter the lobe but incorrectly maps the overall topology of the magnetosphere during these extreme conditions. Dixon, P.; MacDonald, E.; Funsten, H.; Glocer, A.; Grande, M.; Kletzing, C.; Larsen, B.; Reeves, G.; Skoug, R.; Spence, H.; Thomsen, M.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2015 YEAR: 2015 DOI: 10.1002/2014JA020883 Lobes; Magnetosphere; Modelling; Open/closed field line boundary; Van Allen Probes |
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The poloidal waves with large azimuthal wavenumbers (m~100) in the magnetosphere are known to be generated by drift or drift bounce resonance with energetic ring current particles, and these waves may play a role in modulating the energetic particles in the inner magnetosphere. When examining the magnetic field data collected by the NASA ST-5 satellites in the low Earth orbit, Le et al. [2011] discovered many wave events with frequencies of 30\textendash200 mHz (in the Pc 2\textendash3 band), and they proposed that these waves should in fact be Doppler-shifted high-m poloidal waves in the magnetosphere with frequencies at only a few mHz (in the Pc 5 band). Using a new method that examines the differences in wave phase detected by the three ST-5 satellites, we confirm that the frequencies in the Earth frame for the poloidal waves observed are mainly between 3 and 5 mHz. Not only were poloidal waves observed frequently by ST-5 in the dayside magnetosphere, but they were also occasionally seen in the nightside when the satellites passed through the same L shells. In each wave event, the azimuthal wavenumber may change with L, but the wave frequency in the Earth frame remains the same. We also find that poloidal waves can last more than 9 hours during geomagnetically quiet conditions, suggesting that even a very weak ring current can supply enough energetic particles to excite poloidal waves. Published by: Journal of Geophysical Research: Space Physics Published on: 05/2015 YEAR: 2015 DOI: 10.1002/2015JA021145 |
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Simultaneous Pi2 observations by the Van Allen Probes inside and outside the plasmasphere Plasmaspheric virtual resonance (PVR) model has been proposed as one of source mechanisms for low-latitude Pi2 pulsations. Since PVR-associated Pi2 pulsations are not localized inside the plasmasphere, simultaneous multipoint observations inside and outside the plasmasphere require to test the PVR model. Until now, however, there are few studies using simultaneous multisatellite observations inside and outside the plasmasphere for understanding the radial structure of Pi2 pulsation. In this study, we focus on the Pi2 event observed at low-latitude Bohyun (BOH, L = 1.35) ground station in South Korea in the postmidnight sector (magnetic local time (MLT) = 3.0) for the interval from 1730 to 1900 UT on 12 March 2013. By using electron density derived from the frequency of the upper hybrid waves detected at Van Allen Probe-A (VAP-A) and Van Allen Probe-B (VAP-B), the plasmapause is identified. At the time of the Pi2 event, VAP-A was outside the plasmasphere near midnight (00:55 MLT and L = ~6), while VAP-B was inside the plasmasphere in the postmidnight sector (02:15 MLT and L = ~5). VAP-B observed oscillations in the compressional magnetic field component (Bz) and the dawn-to-dusk electric field component (Ey), having high coherence with the BOH Pi2 pulsation in the H component. The H - Bz and H - Ey cross phases at VAP-B inside the plasmasphere were near -180\textdegree and -90\textdegree, respectively.These phase relationships among Bz, Ey, and H are consistent with a radially standing oscillation of the fundamental mode reported in previous studies. At VAP-A outside the plasmasphere, Bz oscillations were highly correlated with BOH Pi2 pulsations with ~-180\textdegree phase delay, and the H-Ey cross phase is near -90\textdegree. From these two-satellite observations, we suggest that the fundamental PVR mode is directly detected by VAP-A and VAP-B. Ghamry, E.; Kim, K.-H.; Kwon, H.-J.; Lee, D.-H.; Park, J.-S.; Choi, J.; Hyun, K.; Kurth, W.; Kletzing, C.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2015 YEAR: 2015 DOI: 10.1002/2015JA021095 Pi2; plasmasphere; Plasmaspheric virtual resonance; Van Allen Probes |
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Simultaneous Pi2 observations by the Van Allen Probes inside and outside the plasmasphere Plasmaspheric virtual resonance (PVR) model has been proposed as one of source mechanisms for low-latitude Pi2 pulsations. Since PVR-associated Pi2 pulsations are not localized inside the plasmasphere, simultaneous multipoint observations inside and outside the plasmasphere require to test the PVR model. Until now, however, there are few studies using simultaneous multisatellite observations inside and outside the plasmasphere for understanding the radial structure of Pi2 pulsation. In this study, we focus on the Pi2 event observed at low-latitude Bohyun (BOH, L = 1.35) ground station in South Korea in the postmidnight sector (magnetic local time (MLT) = 3.0) for the interval from 1730 to 1900 UT on 12 March 2013. By using electron density derived from the frequency of the upper hybrid waves detected at Van Allen Probe-A (VAP-A) and Van Allen Probe-B (VAP-B), the plasmapause is identified. At the time of the Pi2 event, VAP-A was outside the plasmasphere near midnight (00:55 MLT and L = ~6), while VAP-B was inside the plasmasphere in the postmidnight sector (02:15 MLT and L = ~5). VAP-B observed oscillations in the compressional magnetic field component (Bz) and the dawn-to-dusk electric field component (Ey), having high coherence with the BOH Pi2 pulsation in the H component. The H - Bz and H - Ey cross phases at VAP-B inside the plasmasphere were near -180\textdegree and -90\textdegree, respectively.These phase relationships among Bz, Ey, and H are consistent with a radially standing oscillation of the fundamental mode reported in previous studies. At VAP-A outside the plasmasphere, Bz oscillations were highly correlated with BOH Pi2 pulsations with ~-180\textdegree phase delay, and the H-Ey cross phase is near -90\textdegree. From these two-satellite observations, we suggest that the fundamental PVR mode is directly detected by VAP-A and VAP-B. Ghamry, E.; Kim, K.-H.; Kwon, H.-J.; Lee, D.-H.; Park, J.-S.; Choi, J.; Hyun, K.; Kurth, W.; Kletzing, C.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2015 YEAR: 2015 DOI: 10.1002/2015JA021095 Pi2; plasmasphere; Plasmaspheric virtual resonance; Van Allen Probes |
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Statistical characteristic of EMIC waves: Van Allen Probe observations Utilizing the data from the magnetometer instrument which is a part of the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) instrument suite onboard the Van Allen Probe A from Sep. 2012 to Apr. 2014, when the apogee of the satellite has passed all the MLT sectors, we obtain the statistical distribution characteristic of EMIC waves in the inner magnetosphere over all local times from L=3 to L=6. Compared with the previous statistical results about EMIC waves, the occurrence rates of EMIC waves distribute relatively uniform in the MLT sectors in lower L-shells. On the other hand, in higher L-shells, there are indeed some peaks of the occurrence rate for the EMIC waves, especially in the noon, dusk and night sectors. EMIC waves appear at lower L-shells in the dawn sector than in other sectors. In the lower L-shells (L<4), the occurrence rates of EMIC waves are significant in the dawn sector. This phenomenon may result from the distribution characteristic of the plasmasphere. The location of the plasmapause is usually lower in the dawn sector than that in other sectors, and the plasmapause is considered to be the favored region for the generation of EMIC waves. In higher L-shells (L>4) the occurrence rates of EMIC waves are most significant in the dusk sector, implying the important role of the plasmapause or plasmaspheric plume in generating EMIC waves. We have also investigated the distribution characteristics of the hydrogen band and the helium band EMIC waves. Surprisingly, in the inner magnetosphere, the hydrogen band EMIC waves occur more frequently than the helium band EMIC waves. Both them have peaks of occurrence rate in noon, dusk and night sectors, and the hydrogen band EMIC waves have more obvious peaks than the helium band EMIC waves in the night sector, while the helium band EMIC waves are more concentrated than the hydrogen band EMIC waves in the dusk sector. Both them occur significantly in the noon sector, which implies the important role of the solar wind dynamic pressure. Wang, Dedong; Yuan, Zhigang; Yu, Xiongdong; Deng, Xiaohua; Zhou, Meng; Huang, Shiyong; Li, Haimeng; Wang, Zhenzhen; Qiao, Zheng; Kletzing, C.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2015 YEAR: 2015 DOI: 10.1002/2015JA021089 |
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Plasmaspheric hiss is known to play an important role in controlling the overall structure and dynamics of radiation belt electrons inside the plasmasphere. Using newly available Van Allen Probes wave data, which provide excellent coverage in the entire inner magnetosphere, we evaluate the global distribution of the hiss wave frequency spectrum and wave intensity for different levels of substorm activity. Our statistical results show that observed hiss peak frequencies are generally lower than the commonly adopted value (~550 Hz), which was in frequent use, and that the hiss wave power frequently extends below 100 Hz, particularly at larger L shells (> ~3) on the dayside during enhanced levels of substorm activity. We also compare electron pitch angle scattering rates caused by hiss using the new statistical frequency spectrum and the previously adopted Gaussian spectrum and find that the differences are up to a factor of ~5 and are dependent on energy and L shell. Moreover, the new statistical hiss wave frequency spectrum including wave power below 100 Hz leads to increased pitch angle scattering rates by a factor of ~1.5 for electrons above ~100 keV at L~5, although their effect is negligible at L <= 3. Consequently, we suggest that the new realistic hiss wave frequency spectrum should be incorporated into future modeling of radiation belt electron dynamics. Li, W.; Ma, Q.; Thorne, R.; Bortnik, J.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Nishimura, Y.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2015 YEAR: 2015 DOI: 10.1002/2015JA021048 hiss diffusion coefficient; hiss frequency spectrum; Plasmaspheric Hiss; Van Allen Probes |
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Poloidal ULF waves are capable of efficiently interacting with energetic particles in the ring current and the radiation belt. Using Van Allen Probes (RBSP) data from October 2012 to July 2014, we investigate the spatial distribution and storm-time occurrence of Pc4 (7-25 mHz) poloidal waves in the inner magnetosphere. Pc4 poloidal waves are sorted into two categories: waves with and without significant magnetic compressional components. Two types of poloidal waves have comparable occurrence rates, both of which are much higher during geomagnetic storms. The non-compressional poloidal waves mostly occur in the late recovery phase associated with an increase of Dst toward 0, suggesting that the decay of the ring current provides their free energy source. The occurrence of dayside compressional Pc4 poloidal waves is found correlated with the variation of the solar wind dynamic pressure, indicating their origin in the solar wind. Both compressional and non-compressional waves preferentially occur on the dayside near noon at L~5-6. In addition, compressional poloidal waves are observed at MLT 18-24 on the nightside. The location of the Pc4 poloidal waves relative to the plasmapause is investigated. The RBSP statistical results may shed light on the in-depth investigations of the generation and propagation of Pc4 poloidal waves. Dai, Lei; Takahashi, Kazue; Lysak, Robert; Wang, Chi; Wygant, John; Kletzing, Craig; Bonnell, John; Cattell, Cynthia; Smith, Charles; MacDowall, Robert; Thaller, Scott; Breneman, Aaron; Tang, Xiangwei; Tao, Xin; Chen, Lunjin; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2015 YEAR: 2015 DOI: 10.1002/2015JA021134 Geomagnetic storm; Pc4 ULF waves; poloidal waves; ring current; solar wind dynamic pressure; Van Allen Probes |
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Poloidal ULF waves are capable of efficiently interacting with energetic particles in the ring current and the radiation belt. Using Van Allen Probes (RBSP) data from October 2012 to July 2014, we investigate the spatial distribution and storm-time occurrence of Pc4 (7-25 mHz) poloidal waves in the inner magnetosphere. Pc4 poloidal waves are sorted into two categories: waves with and without significant magnetic compressional components. Two types of poloidal waves have comparable occurrence rates, both of which are much higher during geomagnetic storms. The non-compressional poloidal waves mostly occur in the late recovery phase associated with an increase of Dst toward 0, suggesting that the decay of the ring current provides their free energy source. The occurrence of dayside compressional Pc4 poloidal waves is found correlated with the variation of the solar wind dynamic pressure, indicating their origin in the solar wind. Both compressional and non-compressional waves preferentially occur on the dayside near noon at L~5-6. In addition, compressional poloidal waves are observed at MLT 18-24 on the nightside. The location of the Pc4 poloidal waves relative to the plasmapause is investigated. The RBSP statistical results may shed light on the in-depth investigations of the generation and propagation of Pc4 poloidal waves. Dai, Lei; Takahashi, Kazue; Lysak, Robert; Wang, Chi; Wygant, John; Kletzing, Craig; Bonnell, John; Cattell, Cynthia; Smith, Charles; MacDowall, Robert; Thaller, Scott; Breneman, Aaron; Tang, Xiangwei; Tao, Xin; Chen, Lunjin; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2015 YEAR: 2015 DOI: 10.1002/2015JA021134 Geomagnetic storm; Pc4 ULF waves; poloidal waves; ring current; solar wind dynamic pressure; Van Allen Probes |
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A Summary of the BARREL Campaigns: Technique for studying electron precipitation The Balloon Array for Radiation belt Relativistic Electron Losses (BARREL) studies the loss of energetic electrons from Earth\textquoterights radiation belts. BARREL\textquoterights array of slowly drifting balloon payloads was designed to capitalize on magnetic conjunctions with NASA\textquoterights Van Allen Probes. Two campaigns were conducted from Antarctica in 2013 and 2014. During the first campaign in January and February of 2013, there were three moderate geomagnetic storms with Sym-Hmin < -40 nT. Similarly, two minor geomagnetic storms occurred during the second campaign, starting in December of 2013 and continuing on into February of 2014. Throughout the two campaigns, BARREL observed electron precipitation over a wide range of energies and exhibiting temporal structure from 100\textquoterights of milliseconds to hours. Relativistic electron precipitation was observed in the dusk to midnight sector, and microburst precipitation was primarily observed near dawn. In this paper we review the two BARREL science campaigns and discuss the data products and analysis techniques as applied to relativistic electron precipitation observed on 19 January 2013. Woodger, L.; Halford, A.; Millan, R.; McCarthy, M.; Smith, D.; Bowers, G.; Sample, J.; Anderson, B.; Liang, X.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2015 YEAR: 2015 DOI: 10.1002/2014JA020874 electron precipitation; event timing; gamma ray burst; multi-point observation; Radiation belts; Van Allen Probes; x-ray spectroscopy |
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Using the Van Allen Probes we investigate the enhancement in the large scale duskward convection electric field during the geomagnetic storm (Dst ~ -120 nT) on June 1, 2013 and its role in ring current ion transport and energization, and plasmasphere erosion. During this storm, enhancements of ~1-2 mV/m in the duskward electric field in the co-rotating frame are observed down to L shells as low as ~2.3. A simple model consisting of a dipole magnetic field and constant, azimuthally westward, electric field is used to calculate the earthward and westward drift of 90\textdegree pitch angle ions. This model is applied to determine how far earthward ions can drift while remaining on Earth\textquoterights night side, given the strength and duration of the convection electric field. The calculation based on this simple model indicates that the enhanced duskward electric field is of sufficient intensity and duration to transport ions from a range of initial locations and initial energies characteristic of (though not observed by the Van Allen Probes) the earthward edge of the plasma sheet during active times ( L ~ 6\textendash10 and ~1-20 keV) to the observed location of the 58\textendash267 keV ion population, chosen as representative of the ring current (L ~3.5 \textendash 5.8). According to the model calculation, this transportation should be concurrent with an energization to the range observed, ~58-267 keV. Clear coincidence between the electric field enhancement and both plasmasphere erosion and ring current ion (58\textendash267 keV) pressure enhancements are presented. We show for the first time, nearly simultaneous enhancements in the duskward convection electric field, plasmasphere erosion, and increased pressure of 58\textendash267 keV ring current ions. These 58\textendash267 keV ions have energies that are consistent with what they are expected to pick up by gradient B drifting across the electric field. These observations strongly suggest that we are observing the electric field that energizes the ions and produces the erosion of the plasmasphere. Thaller, S.; Wygant, J.; Dai, L.; Breneman, A.W.; Kersten, K.; Cattell, C.A.; Bonnell, J.W.; Fennell, J.F.; Gkioulidou, Matina; Kletzing, C.A.; De Pascuale, S.; Hospodarsky, G.B.; Bounds, S.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2015 YEAR: 2015 DOI: 10.1002/2014JA020875 electric field; inner magnetosphere; plasma convection; plasmasphere; ring current; Van Allen Probes |
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Using the Van Allen Probes we investigate the enhancement in the large scale duskward convection electric field during the geomagnetic storm (Dst ~ -120 nT) on June 1, 2013 and its role in ring current ion transport and energization, and plasmasphere erosion. During this storm, enhancements of ~1-2 mV/m in the duskward electric field in the co-rotating frame are observed down to L shells as low as ~2.3. A simple model consisting of a dipole magnetic field and constant, azimuthally westward, electric field is used to calculate the earthward and westward drift of 90\textdegree pitch angle ions. This model is applied to determine how far earthward ions can drift while remaining on Earth\textquoterights night side, given the strength and duration of the convection electric field. The calculation based on this simple model indicates that the enhanced duskward electric field is of sufficient intensity and duration to transport ions from a range of initial locations and initial energies characteristic of (though not observed by the Van Allen Probes) the earthward edge of the plasma sheet during active times ( L ~ 6\textendash10 and ~1-20 keV) to the observed location of the 58\textendash267 keV ion population, chosen as representative of the ring current (L ~3.5 \textendash 5.8). According to the model calculation, this transportation should be concurrent with an energization to the range observed, ~58-267 keV. Clear coincidence between the electric field enhancement and both plasmasphere erosion and ring current ion (58\textendash267 keV) pressure enhancements are presented. We show for the first time, nearly simultaneous enhancements in the duskward convection electric field, plasmasphere erosion, and increased pressure of 58\textendash267 keV ring current ions. These 58\textendash267 keV ions have energies that are consistent with what they are expected to pick up by gradient B drifting across the electric field. These observations strongly suggest that we are observing the electric field that energizes the ions and produces the erosion of the plasmasphere. Thaller, S.; Wygant, J.; Dai, L.; Breneman, A.W.; Kersten, K.; Cattell, C.A.; Bonnell, J.W.; Fennell, J.F.; Gkioulidou, Matina; Kletzing, C.A.; De Pascuale, S.; Hospodarsky, G.B.; Bounds, S.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2015 YEAR: 2015 DOI: 10.1002/2014JA020875 electric field; inner magnetosphere; plasma convection; plasmasphere; ring current; Van Allen Probes |
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Using the Van Allen Probes we investigate the enhancement in the large scale duskward convection electric field during the geomagnetic storm (Dst ~ -120 nT) on June 1, 2013 and its role in ring current ion transport and energization, and plasmasphere erosion. During this storm, enhancements of ~1-2 mV/m in the duskward electric field in the co-rotating frame are observed down to L shells as low as ~2.3. A simple model consisting of a dipole magnetic field and constant, azimuthally westward, electric field is used to calculate the earthward and westward drift of 90\textdegree pitch angle ions. This model is applied to determine how far earthward ions can drift while remaining on Earth\textquoterights night side, given the strength and duration of the convection electric field. The calculation based on this simple model indicates that the enhanced duskward electric field is of sufficient intensity and duration to transport ions from a range of initial locations and initial energies characteristic of (though not observed by the Van Allen Probes) the earthward edge of the plasma sheet during active times ( L ~ 6\textendash10 and ~1-20 keV) to the observed location of the 58\textendash267 keV ion population, chosen as representative of the ring current (L ~3.5 \textendash 5.8). According to the model calculation, this transportation should be concurrent with an energization to the range observed, ~58-267 keV. Clear coincidence between the electric field enhancement and both plasmasphere erosion and ring current ion (58\textendash267 keV) pressure enhancements are presented. We show for the first time, nearly simultaneous enhancements in the duskward convection electric field, plasmasphere erosion, and increased pressure of 58\textendash267 keV ring current ions. These 58\textendash267 keV ions have energies that are consistent with what they are expected to pick up by gradient B drifting across the electric field. These observations strongly suggest that we are observing the electric field that energizes the ions and produces the erosion of the plasmasphere. Thaller, S.; Wygant, J.; Dai, L.; Breneman, A.W.; Kersten, K.; Cattell, C.A.; Bonnell, J.W.; Fennell, J.F.; Gkioulidou, Matina; Kletzing, C.A.; De Pascuale, S.; Hospodarsky, G.B.; Bounds, S.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2015 YEAR: 2015 DOI: 10.1002/2014JA020875 electric field; inner magnetosphere; plasma convection; plasmasphere; ring current; Van Allen Probes |
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We investigate an electron flux dropout during a weak storm on 7\textendash8 November 2008, with Dst minimum value being -37 nT. During this period, two clear dropouts were observed on GOES 11 > 2 MeV electrons. We also find a simultaneous dropout in the subrelativistic electrons recorded by Time History of Events and Macroscale Interactions during Substorms probes in the outer radiation belt. Using the Radiation Belt Environment model, we try to reproduce the observed dropout features in both relativistic and subrelativistic electrons. We found that there are local time dependences in the dropout for both observation and simulation in subrelativistic electrons: (1) particle loss begins from nightside and propagates into dayside and (2) resupply starts from near dawn magnetic local time and propagates into the dayside following electron drift direction. That resupply of the particles might be caused by substorm injections due to enhanced convection. We found a significant precipitation in hundreds keV electrons during the dropout. We observe electromagnetic ion cyclotron and chorus waves both on the ground and in space. We find the drift shells are opened near the beginning of the first dropout. The dropout in MeV electrons at GEO might therefore be initiated due to the magnetopause shadowing, and the followed dropout in hundreds keV electrons might be the result of the combination of magnetopause shadowing and precipitation loss into the Earth\textquoterights atmosphere. Hwang, J.; Choi, E.-J.; Park, J.-S.; Fok, M.-C.; Lee, D.-Y.; Kim, K.-C.; Shin, D.-K.; Usanova, M.; Reeves, G.; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2015 YEAR: 2015 DOI: 10.1002/2015JA021085 atmospheric precipitation; flux dropout; Geomagnetic storm; magneopause shadowing; Radiation belt; RBE model |
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Tracking the formation and full evolution of polar cap ionization patches in the polar ionosphere, we directly observe the full Dungey convection cycle for southward interplanetary magnetic field (IMF) conditions. This enables us to study how the Dungey cycle influences the patches\textquoteright evolution. The patches were initially segmented from the dayside storm enhanced density plume (SED) at the equatorward edge of the cusp, by the expansion and contraction of the polar cap boundary (PCB) due to pulsed dayside magnetopause reconnection, as indicated by in-situ THEMIS observations. Convection led to the patches entering the polar cap and being transported antisunward, whilst being continuously monitored by the globally distributed arrays of GPS receivers and SuperDARN radars. Changes in convection over time resulted in the patches following a range of trajectories, each of which differed somewhat from the classical twin-cell convection streamlines. Pulsed nightside reconnection, occurring as part of the magnetospheric substorm cycle, modulated the exit of the patches from the polar cap, as confirmed by coordinated observations of the magnetometer at Troms\o and EISCAT Troms\o UHF Radar. After exiting the polar cap, the patches broke up into a number of plasma blobs, and returned sunward in the auroral return flow of the dawn and/or dusk convection cell. The full circulation time was about three hours. Zhang, Q.; Lockwood, M.; Foster, J.; Zhang, S.; Zhang, B.; McCrea, I.; Moen, J.; Lester, M.; Ruohoniemi, Michael; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2015 YEAR: 2015 DOI: 10.1002/2015JA021172 Dungey convection cycle; EISCAT radar; GPS TEC; polar cap patches |
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Equatorial noise emissions with quasiperiodic modulation of wave intensity Equatorial noise (EN) emissions are electromagnetic wave events at frequencies between the proton cyclotron frequency and the lower hybrid frequency observed in the equatorial region of the inner magnetosphere. They propagate nearly perpendicular to the ambient magnetic field, and they exhibit a harmonic line structure characteristic of the proton cyclotron frequency in the source region. However, they were generally believed to be continuous in time. We investigate more than 2000 EN events observed by the Spatio-Temporal Analysis of Field Fluctuations and Wide-Band Data Plasma Wave investigation instruments on board the Cluster spacecraft, and we show that this is not always the case. A clear quasiperiodic (QP) time modulation of the wave intensity is present in more than 5\% of events. We perform a systematic analysis of these EN events with QP modulation of the wave intensity. Such events occur usually in the noon-to-dawn magnetic local time sector. Their occurrence seems to be related to the increased geomagnetic activity, and it is associated with the time intervals of enhanced solar wind flow speeds. The modulation period of these events is on the order of minutes. Compressional ULF magnetic field pulsations with periods about double the modulation periods of EN wave intensity and magnitudes on the order of a few tenths of nanotesla were identified in about 46\% of events. We suggest that these compressional magnetic field pulsations might be responsible for the observed QP modulation of EN wave intensity, in analogy to formerly reported VLF whistler mode QP events. emec, F.; Santolik, O.; a, Hrb\; Pickett, J.; Cornilleau-Wehrlin, N.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2014JA020816 equatorial noise; magnetosonic waves; quasiperiodic modulation |
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It is well known that the plasmapause is influenced by the solar wind and magnetospheric conditions. Empirical models of its location have been previously developed such as those by O\textquoterightBrien and Moldwin (2003) and Larsen et al. (2006). In this study, we identified the locations of the plasmapause using the plasma density data obtained from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites. We used the data for the period (2008\textendash2012) corresponding to the ascending phase of Solar Cycle 24. Our database includes data from over a year of unusually weak solar wind conditions, correspondingly covering the plasmapause locations in a wider L range than those in previous studies. It also contains many coronal hole stream intervals during which the plasmasphere is eroded and recovers over a timescale of several days. The plasmapause was rigorously determined by requiring a density gradient by a factor of 15 within a radial distance of 0.5 L. We first determined the statistical correlation of the plasmapause locations with several solar wind parameters as well as geomagnetic indices. We found that the plasmapause locations are well correlated with the solar wind speed and the interplanetary magnetic field Bz, therefore the y component of the convective electric field, and some energy coupling functions such as the well-known Akasofu\textquoterights epsilon parameter. The plasmapause locations are also highly correlated with the geomagnetic indices, Dst, AE, and Kp, as recognized previously. Finally, we suggest new model fit functions for the plasmapause locations in terms of the solar wind parameters and geomagnetic indices. When applied to a new data interval outside the model training interval, our model fit functions work better than existing ones. The new model fit functions developed here extend the range of conditions from those used in previous works. Cho, Junghee; Lee, Dae-Young; Kim, Jin-Hee; Shin, Dae-Kyu; Kim, Kyung-Chan; Turner, Drew; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2015JA021030 |
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Whistler mode chorus waves are considered to play a central role in accelerating and scattering electrons in the outer radiation belt. While in situ measurements are usually limited to the trajectories of a small number of satellites, rigorous theoretical modeling requires a global distribution of chorus wave characteristics. In the present work, by using a large database of chorus wave observations made on the Time History of Events and Macroscale Interactions during Substorms satellites for about 5 years, we develop prediction models for a global distribution of chorus amplitudes. The development is based on two main components: (a) the temporal dependence of average chorus amplitudes determined by correlating with the preceding solar wind and geomagnetic conditions as represented by the interplanetary magnetic field (IMF) Bz and AE index and (b) the determination of spatial distribution pattern of chorus amplitudes, specifically, the profiles in L in all 2 h magnetic local time zones, which are categorized by activity levels of either the IMF Bz or AE index. Two separate models are developed: one based only on the IMF Bz and the other based only on AE. Both models predict chorus amplitudes for two different latitudinal zones separately: |magnetic latitude (MLAT)| < 10\textdegree, and |MLAT| = 10\textdegree\textendash25\textdegree. The model performance is measured by the coefficient of determination R2 and the rank-order correlation coefficient (ROCC) between the observations and model prediction results. When tested for a new data interval of ~1.5 years, the AE-based model works slightly better than the IMF Bz-based model: for the AE-based model, the mean R2 and ROCC values are ~0.46 and ~0.78 for |MLAT| < 10\textdegree, respectively, and ~0.4 and ~0.74 for |MLAT| = 10\textdegree\textendash25\textdegree, respectively; for the IMF Bz-based model, the mean R2 and ROCC values are ~0.39 and ~0.74 for |MLAT| < 10\textdegree, respectively, and ~0.33 and ~0.70 for |MLAT| = 10\textdegree\textendash25\textdegree, respectively. We provide all of the model information in the text and supporting information so that the developed chorus models can be used for the existing outer radiation belt electron models. Kim, Jin-Hee; Lee, Dae-Young; Cho, Jung-Hee; Shin, Dae-Kyu; Kim, Kyung-Chan; Li, Wen; Kim, Thomas; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2014JA020900 |
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Solar cycle dependence of ion cyclotron wave frequencies Electromagnetic ion cyclotron (EMIC) waves have been studied for decades, though remain a fundamentally important topic in heliospheric physics. The connection of EMIC waves to the scattering of energetic particles from Earth\textquoterights radiation belts is one ofmany topics that motivate the need for a deeper understanding of characteristics and occurrence distributions of the waves. In this study, we show that EMIC wave frequencies, as observed at Halley Station in Antarctica from 2008 through 2012, increase by approximately 60\% from a minimum in 2009 to the end of 2012. Assuming that these waves are excited in the vicinity of the plasmapause, the change in Kp in going from solar minimum to near solar maximum would drive increased plasmapause erosion, potentially shifting the generation region of the EMIC to lower L and resulting in the higher frequencies. A numerical estimate of the change in plasmapause location, however, implies that it is not enough to account for the shift in EMIC frequencies that are observed at Halley Station. Another possible explanation for the frequency shift, however, is that the relative density of heavier ions in the magnetosphere (that would be associated with increased solar activity) could account for the change in frequencies. In terms of effects on radiation belt dynamics, the shift to higher frequencies tends to mean that these waves will interact with less energetic electrons, although the details involved in this process are complex and depend on the specific plasma and gyrofrequencies of all populations, including electrons. In addition, the change in location of the generation region to lower L shells means that the waves will have access to higher number fluxes of resonant electrons. Finally, we show a sunlit ionosphere can inhibit ground observations of EMIC waves with frequencies higher than ~0.5 Hz and note that the effect likely has resulted in an underestimate of the solar-cycle-driven frequency changes described here. Lessard, Marc; Lindgren, Erik; Engebretson, Mark; Weaver, Carol; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2014JA020791 EMIC waves; Ion cyclotron; Magnetosphere; plasma waves; Radiation belts; solar cycles |
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Time Domain Structures: what and where they are, what they do, and how they are made Time Domain Structures (TDS) (electrostatic or electromagnetic electron holes, solitary waves, double layers, etc.) are >=1 msec pulses having significant parallel (to the background magnetic field) electric fields. They are abundant through space and occur in packets of hundreds in the outer Van Allen radiation belts where they produce magnetic-field-aligned electron pitch angle distributions at energies up to a hundred keV. TDS can provide the seed electrons that are later accelerated to relativistic energies by whistlers and they also produce field-aligned electrons that may be responsible for some types of auroras. These field-aligned electron distributions result from at least three processes. The first process is parallel acceleration by Landau trapping in the TDS parallel electric field. The second process is Fermi acceleration due to reflection of electrons by the TDS. The third process is an effective and rapid pitch angle scattering resulting from electron interactions with the perpendicular and parallel electric and magnetic fields of many TDS. TDS are created by current-driven and beam-related instabilities and by whistler-related processes such as parametric decay of whistlers and non-linear evolution from oblique whistlers. New results on the temporal relationship of TDS and particle injections, types of field-aligned electron pitch angle distributions produced by TDS, the mechanisms for generation of field-aligned distributions by TDS, the maximum energies of field-aligned electrons created by TDS in the absence of whistler mode waves, TDS generation by oblique whistlers and three-wave-parametric decay, and the correlation between TDS and auroral particle precipitation, are presented. Mozer, F.S.; Agapitov, O.V.; Artemyev, A.; Drake, J.F.; Krasnoselskikh, V.; Lejosne, S.; Vasko, I.; Published by: Geophysical Research Letters Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2015GL063946 |
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A novel technique capable of inferring wave amplitudes from low-altitude electron measurements from the POES spacecraft has been previously proposed to construct a global dynamic model of chorus and plasmaspheric hiss waves. In this paper we focus on plasmaspheric hiss, which is an incoherent broadband emission that plays a dominant role in the loss of energetic electrons from the inner magnetosphere. We analyze the sensitivity of the POES technique to different inputs used to infer the hiss wave amplitudes during three conjunction events with the Van Allen Probes. These amplitudes are calculated with different input models of the plasma density, wave frequency spectrum, and electron energy spectrum, and the results are compared to the wave observations from the twin Van Allen Probes. Only one parameter is varied at a time in order to isolate its effect on the output, while the two other inputs are set to the values observed by the Van Allen Probes. The results show that the predicted hiss amplitudes are most sensitive to the adopted frequency spectrum, followed by the plasma density, but they are not very sensitive to the electron energy spectrum. Moreover, the standard Gaussian representation of the wave frequency spectrum (centered at 550 Hz) peaks at frequencies that are much higher than those observed in individual cases as well as in statistical wave distributions, which produces large overestimates of the hiss wave amplitude. For this reason, a realistic statistical model of the wave frequency spectrum should be used in the POES technique to infer the plasmaspheric hiss wave intensity rather than a standard Gaussian distribution, since the former better reproduces the observed plasmaspheric hiss wave amplitudes. de Soria-Santacruz, M.; Li, W.; Thorne, R.; Ma, Q.; Bortnik, J.; Ni, B.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Reeves, G.D.; Blake, J.; Fennell, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2014JA020941 Plasmaspheric Hiss; POES technique; Van Allen Probes; Waves global model |
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Electron precipitation from EMIC waves: a case study from 31 May 2013 On 31 May 2013 several rising-tone electromagnetic ion-cyclotron (EMIC) waves with intervals of pulsations of diminishing periods (IPDP) were observed in the magnetic local time afternoon and evening sectors during the onset of a moderate/large geomagnetic storm. The waves were sequentially observed in Finland, Antarctica, and western Canada. Co-incident electron precipitation by a network of ground-based Antarctic Arctic Radiation-belt Dynamic Deposition VLF Atmospheric Research Konsortia (AARDDVARK) and riometer instruments, as well as the Polar-orbiting Operational Environmental Satellite (POES) electron telescopes, was also observed. At the same time POES detected 30-80 keV proton precipitation drifting westwards at locations that were consistent with the ground-based observations, indicating substorm injection. Through detailed modelling of the combination of ground and satellite observations the characteristics of the EMIC-induced electron precipitation were identified as: latitudinal width of 2-3\textdegree or ΔL=1 Re, longitudinal width ~50\textdegree or 3 hours MLT, lower cut off energy 280 keV, typical flux 1\texttimes104 el. cm-2 sr-1 s-1 >300 keV. The lower cutoff energy of the most clearly defined EMIC rising tone in this study confirms the identification of a class of EMIC-induced precipitation events with unexpectedly low energy cutoffs of <400 keV. Clilverd, Mark; Duthie, Roger; Hardman, Rachael; Hendry, Aaron; Rodger, Craig; Raita, Tero; Engebretson, Mark; Lessard, Marc; Danskin, Donald; Milling, David; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2015JA021090 electromagnetic ion-cyclotron; electron precipitation; radio propagation; satellite |
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An empirical model of electron and ion fluxes derived from observations at geosynchronous orbit Knowledge of the plasma fluxes at geosynchronous orbit is important to both scientific and operational investigations. We present a new empirical model of the ion flux and the electron flux at geosynchronous orbit (GEO) in the energy range ~1 eV to ~40 keV. The model is based on a total of 82 satellite years of observations from the magnetospheric plasma analyzer instruments on Los Alamos National Laboratory satellites at GEO. These data are assigned to a fixed grid of 24 local times and 40 energies, at all possible values of Kp. Bilinear interpolation is used between grid points to provide the ion flux and the electron flux values at any energy and local time, and for given values of geomagnetic activity (proxied by the 3 h Kp index), and also for given values of solar activity (proxied by the daily F10.7 index). Initial comparison of the electron flux from the model with data from a Compact Environmental Anomaly Sensor II, also located at geosynchronous orbit, indicates a good match during both quiet and disturbed periods. The model is available for distribution as a FORTRAN code that can be modified to suit user requirements. Denton, M.; Thomsen, M.; Jordanova, V.; Henderson, M.; Borovsky, J.; Denton, J.; Pitchford, D.; Hartley, D.; Published by: Space Weather Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2015SW001168 |
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In this study, we compare long-term simulations performed by the Versatile Electron Radiation Belt (VERB) code with observations from the MagEIS and REPT instruments on the Van Allen Probes satellites. The model takes into account radial, energy, pitch-angle and mixed diffusion, losses into the atmosphere, and magnetopause shadowing. We consider the energetic (>100 keV), relativistic (~0.5-1 MeV) and ultra-relativistic (>2 MeV) electrons. One year of relativistic electron measurements (μ=700 MeV/G) from October 1, 2012 to October 1, 2013, are well reproduced by the simulation during varying levels of geomagnetic activity. However, for ultra-relativistic energies (μ=3500 MeV/G), the VERB code simulation overestimates electron fluxes and Phase Space Density. These results indicate that an additional loss mechanism is operational and efficient for these high energies. The most likely mechanism for explaining the observed loss at ultra-relativistic energies is scattering by the Electro-Magnetic Ion Cyclotron waves. Drozdov, A; Shprits, Y; Orlova, K.G.; Kellerman, A.; Subbotin, D.; Baker, D.; Spence, H.E.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2014JA020637 EMIC waves; Long-term simulation; Van Allen Probes; VERB code |
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High-energy radiation belt electrons from CRAND A calculation of the inner radiation belt electron source from cosmic ray albedo neutron decay (CRAND) is described. High-energy electrons are included by Lorentz-transforming the β decay spectrum from the neutron rest frame to the Earth\textquoterights rest frame and combining with the known high-energy albedo neutron energy spectrum. Balancing the electron source with energy loss to atmospheric neutral atoms and plasma, and with a decay lifetime representative of plasma wave scattering, then provides an estimate of trapped electron intensity. It is well below measured values for low energies, confirming that CRAND is not a significant source of those trapped electrons. For kinetic energies above the maximum β decay energy (E > 0.8 MeV) a power law energy spectrum \~E-4 is predicted. For L = 1.5 and inline image MeV the computed omnidirectional trapped electron intensity exceeds an extrapolation of the measured low-energy exponential energy spectrum. Published by: Journal of Geophysical Research: Space Physics Published on: 03/2015 YEAR: 2015 DOI: 10.1002/2014JA020963 inner radiation; electron source from cosmic ray albedo neutron decay |
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Equatorial noise (EN) emissions are electromagnetic waves observed in the equatorial region of the inner magnetosphere at frequencies between the proton cyclotron frequency and the lower hybrid frequency. We present the analysis of 2229 EN events identified in the Spatio-Temporal Analysis of Field Fluctuations (STAFF) experiment data of the Cluster spacecraft during the years 2001\textendash2010. EN emissions are distinguished using the polarization analysis, and their intensity is determined based on the evaluation of the Poynting flux rather than on the evaluation of only the electric/magnetic field intensity. The intensity of EN events is analyzed as a function of the frequency, the position of the spacecraft inside/outside the plasmasphere, magnetic local time, and the geomagnetic activity. The emissions have higher frequencies and are more intense in the plasma trough than in the plasmasphere. EN events observed in the plasma trough are most intense close to the local noon, while EN events observed in the plasmasphere are nearly independent on magnetic local time (MLT). The intensity of EN events is enhanced during disturbed periods, both inside the plasmasphere and in the plasma trough. Observations of the same events by several Cluster spacecraft allow us to estimate their spatiotemporal variability. EN emissions observed in the plasmasphere do not change on the analyzed spatial scales (ΔMLT<0.2h, Δr<0.2 RE), but they change significantly on time scales of about an hour. The same appears to be the case also for EN events observed in the plasma trough, although the plasma trough dependencies are less clear. emec, F.; Santolik, O.; a, Hrb\; Cornilleau-Wehrlin, N.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2015 YEAR: 2015 DOI: 10.1002/2014JA020814 |
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Study of EMIC wave excitation using direct ion measurements With data from Van Allen Probes, we investigate EMIC wave excitation using simultaneously observed ion distributions. Strong He-band waves occurred while the spacecraft was moving through an enhanced density region. We extract from Helium, Oxygen, Proton, and Electron (HOPE) Mass Spectrometer measurement the velocity distributions of warm heavy ions as well as anisotropic energetic protons that drive wave growth through the ion cyclotron instability. Fitting the measured ion fluxes to multiple sinm-type distribution functions, we find that the observed ions make up about 15\% of the total ions, but about 85\% of them are still missing. By making legitimate estimates of the unseen cold (below ~2 eV) ion composition from cutoff frequencies suggested by the observed wave spectrum, a series of linear instability analyses and hybrid simulations are carried out. The simulated waves generally vary as predicted by linear theory. They are more sensitive to the cold O+ concentration than the cold He+ concentration. Increasing the cold O+ concentration weakens the He-band waves but enhances the O-band waves. Finally, the exact cold ion composition is suggested to be in a range when the simulated wave spectrum best matches the observed one. Min, Kyungguk; Liu, Kaijun; Bonnell, John; Breneman, Aaron; Denton, Richard; Funsten, Herbert; Jahn, öerg-Micha; Kletzing, Craig; Kurth, William; Larsen, Brian; Reeves, Geoffrey; Spence, Harlan; Wygant, John; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2015 YEAR: 2015 DOI: 10.1002/2014JA020717 EMIC wave excitation; observation; linear theory and hybrid simulation; Van Allen Probes |