Bibliography
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Found 3761 entries in the Bibliography.
Showing entries from 2801 through 2850
| 2015 |
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Role of turbulent transport in the evolution of the κ distribution functions in the plasma sheet We studied the evolution of ion and electron distribution functions, approximated by κ distributions, in the plasma sheet with the distance from the Earth using the data of the THEMIS spacecraft mission. Five events were used to calculate the main parameters of the κ distribution. For these events at least four spacecraft were aligned along the tail between approximately 7 and 30 Earth radii. It was found that for the majority of events the values of κ increase tailwards. The observed radial profiles could be related to the inner magnetosphere sources of particle acceleration and to the net tailward transport of particles. This net transport is the result of a balance between the average regular bulk transport toward the Earth and the turbulent transport by eddies in the tailward direction. Stepanova, Marina; Antonova, Elizaveta; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2014JA020684 |
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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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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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We present a case study of eight successive plasma sheet (PS) activations (usually referred to as bursty bulk flows or dipolarization fronts ) associated with small individual inline image increases on 31 March 2009 (0200\textendash0900 UT), observed by the THEMIS mission. This series of events happens during very quiet solar wind conditions, over a period of 7 hours preceding a substorm onset at 1230 UT. The amplitude of the dipolarizations increases with time. The low-amplitude dipolarization fronts are associated with few (1 or 2) rapid flux transport events (RFT, Eh > 2mV/m), whereas the large-amplitude ones encompass many more RFT events. All PS activations are associated with small and localized substorm current wedge (SCW) like current system signatures, which seems to be the consequence of RFT arrival in the near tail. The associated ground magnetic perturbations affect a larger part of the contracted auroral oval when, in the magnetotail, more RFT are embedded in PS activations (> 5). Dipolarization fronts with very low amplitude, a type usually not included in statistical studies, are of particular interest because we found even those to be associated with clear small SCW-like current system and particle injections at geosynchronous orbit. This exceptional dataset highlights the role of flow bursts in the magnetotail and leads to the conclusion that we may be observing the smallest form of a substorm, or rather its smallest element. This study also highlights the gradual evolution of the ionospheric current disturbance as the plasma sheet is observed to heat-up. Palin, L.; Jacquey, C.; Opgenoorth, H.; Connors, M.; Sergeev, V.; Sauvaud, J.-A.; Nakamura, R.; Reeves, G.D.; Singer, H.J.; Angelopoulos, V.; Turc, L.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2015JA021040 bursty bulk flow; dipolarization front; field-aligned currents; substorm; substorm current wedge; wedgelet |
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We present a case study of eight successive plasma sheet (PS) activations (usually referred to as bursty bulk flows or dipolarization fronts ) associated with small individual inline image increases on 31 March 2009 (0200\textendash0900 UT), observed by the THEMIS mission. This series of events happens during very quiet solar wind conditions, over a period of 7 hours preceding a substorm onset at 1230 UT. The amplitude of the dipolarizations increases with time. The low-amplitude dipolarization fronts are associated with few (1 or 2) rapid flux transport events (RFT, Eh > 2mV/m), whereas the large-amplitude ones encompass many more RFT events. All PS activations are associated with small and localized substorm current wedge (SCW) like current system signatures, which seems to be the consequence of RFT arrival in the near tail. The associated ground magnetic perturbations affect a larger part of the contracted auroral oval when, in the magnetotail, more RFT are embedded in PS activations (> 5). Dipolarization fronts with very low amplitude, a type usually not included in statistical studies, are of particular interest because we found even those to be associated with clear small SCW-like current system and particle injections at geosynchronous orbit. This exceptional dataset highlights the role of flow bursts in the magnetotail and leads to the conclusion that we may be observing the smallest form of a substorm, or rather its smallest element. This study also highlights the gradual evolution of the ionospheric current disturbance as the plasma sheet is observed to heat-up. Palin, L.; Jacquey, C.; Opgenoorth, H.; Connors, M.; Sergeev, V.; Sauvaud, J.-A.; Nakamura, R.; Reeves, G.D.; Singer, H.J.; Angelopoulos, V.; Turc, L.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2015JA021040 bursty bulk flow; dipolarization front; field-aligned currents; substorm; substorm current wedge; wedgelet |
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We present a case study of eight successive plasma sheet (PS) activations (usually referred to as bursty bulk flows or dipolarization fronts ) associated with small individual inline image increases on 31 March 2009 (0200\textendash0900 UT), observed by the THEMIS mission. This series of events happens during very quiet solar wind conditions, over a period of 7 hours preceding a substorm onset at 1230 UT. The amplitude of the dipolarizations increases with time. The low-amplitude dipolarization fronts are associated with few (1 or 2) rapid flux transport events (RFT, Eh > 2mV/m), whereas the large-amplitude ones encompass many more RFT events. All PS activations are associated with small and localized substorm current wedge (SCW) like current system signatures, which seems to be the consequence of RFT arrival in the near tail. The associated ground magnetic perturbations affect a larger part of the contracted auroral oval when, in the magnetotail, more RFT are embedded in PS activations (> 5). Dipolarization fronts with very low amplitude, a type usually not included in statistical studies, are of particular interest because we found even those to be associated with clear small SCW-like current system and particle injections at geosynchronous orbit. This exceptional dataset highlights the role of flow bursts in the magnetotail and leads to the conclusion that we may be observing the smallest form of a substorm, or rather its smallest element. This study also highlights the gradual evolution of the ionospheric current disturbance as the plasma sheet is observed to heat-up. Palin, L.; Jacquey, C.; Opgenoorth, H.; Connors, M.; Sergeev, V.; Sauvaud, J.-A.; Nakamura, R.; Reeves, G.D.; Singer, H.J.; Angelopoulos, V.; Turc, L.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2015JA021040 bursty bulk flow; dipolarization front; field-aligned currents; substorm; substorm current wedge; wedgelet |
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We present a case study of eight successive plasma sheet (PS) activations (usually referred to as bursty bulk flows or dipolarization fronts ) associated with small individual inline image increases on 31 March 2009 (0200\textendash0900 UT), observed by the THEMIS mission. This series of events happens during very quiet solar wind conditions, over a period of 7 hours preceding a substorm onset at 1230 UT. The amplitude of the dipolarizations increases with time. The low-amplitude dipolarization fronts are associated with few (1 or 2) rapid flux transport events (RFT, Eh > 2mV/m), whereas the large-amplitude ones encompass many more RFT events. All PS activations are associated with small and localized substorm current wedge (SCW) like current system signatures, which seems to be the consequence of RFT arrival in the near tail. The associated ground magnetic perturbations affect a larger part of the contracted auroral oval when, in the magnetotail, more RFT are embedded in PS activations (> 5). Dipolarization fronts with very low amplitude, a type usually not included in statistical studies, are of particular interest because we found even those to be associated with clear small SCW-like current system and particle injections at geosynchronous orbit. This exceptional dataset highlights the role of flow bursts in the magnetotail and leads to the conclusion that we may be observing the smallest form of a substorm, or rather its smallest element. This study also highlights the gradual evolution of the ionospheric current disturbance as the plasma sheet is observed to heat-up. Palin, L.; Jacquey, C.; Opgenoorth, H.; Connors, M.; Sergeev, V.; Sauvaud, J.-A.; Nakamura, R.; Reeves, G.D.; Singer, H.J.; Angelopoulos, V.; Turc, L.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2015JA021040 bursty bulk flow; dipolarization front; field-aligned currents; substorm; substorm current wedge; wedgelet |
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We present a case study of eight successive plasma sheet (PS) activations (usually referred to as bursty bulk flows or dipolarization fronts ) associated with small individual inline image increases on 31 March 2009 (0200\textendash0900 UT), observed by the THEMIS mission. This series of events happens during very quiet solar wind conditions, over a period of 7 hours preceding a substorm onset at 1230 UT. The amplitude of the dipolarizations increases with time. The low-amplitude dipolarization fronts are associated with few (1 or 2) rapid flux transport events (RFT, Eh > 2mV/m), whereas the large-amplitude ones encompass many more RFT events. All PS activations are associated with small and localized substorm current wedge (SCW) like current system signatures, which seems to be the consequence of RFT arrival in the near tail. The associated ground magnetic perturbations affect a larger part of the contracted auroral oval when, in the magnetotail, more RFT are embedded in PS activations (> 5). Dipolarization fronts with very low amplitude, a type usually not included in statistical studies, are of particular interest because we found even those to be associated with clear small SCW-like current system and particle injections at geosynchronous orbit. This exceptional dataset highlights the role of flow bursts in the magnetotail and leads to the conclusion that we may be observing the smallest form of a substorm, or rather its smallest element. This study also highlights the gradual evolution of the ionospheric current disturbance as the plasma sheet is observed to heat-up. Palin, L.; Jacquey, C.; Opgenoorth, H.; Connors, M.; Sergeev, V.; Sauvaud, J.-A.; Nakamura, R.; Reeves, G.D.; Singer, H.J.; Angelopoulos, V.; Turc, L.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2015JA021040 bursty bulk flow; dipolarization front; field-aligned currents; substorm; substorm current wedge; wedgelet |
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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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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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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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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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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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Unraveling the drivers of the storm time radiation belt response We present a new framework to study the time evolution and dynamics of the outer Van Allen belt electron fluxes. The framework is entirely based on the large-scale solar wind storm drivers and their substructures. The Van Allen Probe observations, revealing the electron flux behavior throughout the outer belt, are combined with continuous, long-term (over 1.5 solar cycles) geosynchronous orbit data set from GOES and solar wind measurements A superposed epoch analysis, where we normalize the timescales for each substructure (sheath, ejecta, and interface region) allows us to avoid smearing effects and to distinguish the electron flux evolution during various driver structures. We show that the radiation belt response is not random: The electron flux variations are determined by the combined effect of the structured solar wind driver and prestorm electron flux levels. In particular, we find that loss mechanisms dominate during stream interface regions, coronal mass ejection (CME) ejecta, and sheaths while enhancements occur during fast streams trailing the stream interface or the CME. Kilpua, E.; Hietala, H.; Turner, D.; Koskinen, H.; Pulkkinen, T.; Rodriguez, J.; Reeves, G.; Claudepierre, S.; Spence, H.; Published by: Geophysical Research Letters Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2015GL063542 coronal mass ejections; Magnetic Storms; Radiation belts; solar wind storm drivers; stream interaction regions; Van Allen Probes |
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Unraveling the drivers of the storm time radiation belt response We present a new framework to study the time evolution and dynamics of the outer Van Allen belt electron fluxes. The framework is entirely based on the large-scale solar wind storm drivers and their substructures. The Van Allen Probe observations, revealing the electron flux behavior throughout the outer belt, are combined with continuous, long-term (over 1.5 solar cycles) geosynchronous orbit data set from GOES and solar wind measurements A superposed epoch analysis, where we normalize the timescales for each substructure (sheath, ejecta, and interface region) allows us to avoid smearing effects and to distinguish the electron flux evolution during various driver structures. We show that the radiation belt response is not random: The electron flux variations are determined by the combined effect of the structured solar wind driver and prestorm electron flux levels. In particular, we find that loss mechanisms dominate during stream interface regions, coronal mass ejection (CME) ejecta, and sheaths while enhancements occur during fast streams trailing the stream interface or the CME. Kilpua, E.; Hietala, H.; Turner, D.; Koskinen, H.; Pulkkinen, T.; Rodriguez, J.; Reeves, G.; Claudepierre, S.; Spence, H.; Published by: Geophysical Research Letters Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2015GL063542 coronal mass ejections; Magnetic Storms; Radiation belts; solar wind storm drivers; stream interaction regions; Van Allen Probes |
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Unraveling the drivers of the storm time radiation belt response We present a new framework to study the time evolution and dynamics of the outer Van Allen belt electron fluxes. The framework is entirely based on the large-scale solar wind storm drivers and their substructures. The Van Allen Probe observations, revealing the electron flux behavior throughout the outer belt, are combined with continuous, long-term (over 1.5 solar cycles) geosynchronous orbit data set from GOES and solar wind measurements A superposed epoch analysis, where we normalize the timescales for each substructure (sheath, ejecta, and interface region) allows us to avoid smearing effects and to distinguish the electron flux evolution during various driver structures. We show that the radiation belt response is not random: The electron flux variations are determined by the combined effect of the structured solar wind driver and prestorm electron flux levels. In particular, we find that loss mechanisms dominate during stream interface regions, coronal mass ejection (CME) ejecta, and sheaths while enhancements occur during fast streams trailing the stream interface or the CME. Kilpua, E.; Hietala, H.; Turner, D.; Koskinen, H.; Pulkkinen, T.; Rodriguez, J.; Reeves, G.; Claudepierre, S.; Spence, H.; Published by: Geophysical Research Letters Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2015GL063542 coronal mass ejections; Magnetic Storms; Radiation belts; solar wind storm drivers; stream interaction regions; Van Allen Probes |
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Very Oblique Whistler Generation By Low Energy Electron Streams Whistler-mode chorus waves are present throughout the Earth\textquoterights outer radiation belt as well as at larger distances from our planet. While the generation mechanisms of parallel lower-band chorus waves and oblique upper-band chorus waves have been identified and checked in various instances, the statistically significant presence in recent satellite observations of very oblique lower-band chorus waves near the resonance cone angle remains to be explained. Here we discuss two possible generation mechanisms for such waves. The first one is based on Landau resonance with sporadic very low energy (<4 keV) electron beams either injected from the plasmasheet or produced in situ. The second one relies on cyclotron resonance with low energy electron streams, such that their velocity distribution possesses both a significant temperature anisotropy above 3-4 keV and a plateau or heavy tail in parallel velocities at lower energies encompassing simultaneous Landau resonance with the same waves. The corresponding frequency and wave normal angle distributions of the generated very oblique lower-band chorus waves, as well as their frequency sweep rate, are evaluated analytically and compared with satellite observations, showing a reasonable agreement. Mourenas, D.; Artemyev, A.; Agapitov, O.; Krasnoselskikh, V.; Mozer, F.S.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2015JA021135 Chorus wave; Cyclotron resonance; Landau resonance; oblique whistler; wave generation |
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Very Oblique Whistler Generation By Low Energy Electron Streams Whistler-mode chorus waves are present throughout the Earth\textquoterights outer radiation belt as well as at larger distances from our planet. While the generation mechanisms of parallel lower-band chorus waves and oblique upper-band chorus waves have been identified and checked in various instances, the statistically significant presence in recent satellite observations of very oblique lower-band chorus waves near the resonance cone angle remains to be explained. Here we discuss two possible generation mechanisms for such waves. The first one is based on Landau resonance with sporadic very low energy (<4 keV) electron beams either injected from the plasmasheet or produced in situ. The second one relies on cyclotron resonance with low energy electron streams, such that their velocity distribution possesses both a significant temperature anisotropy above 3-4 keV and a plateau or heavy tail in parallel velocities at lower energies encompassing simultaneous Landau resonance with the same waves. The corresponding frequency and wave normal angle distributions of the generated very oblique lower-band chorus waves, as well as their frequency sweep rate, are evaluated analytically and compared with satellite observations, showing a reasonable agreement. Mourenas, D.; Artemyev, A.; Agapitov, O.; Krasnoselskikh, V.; Mozer, F.S.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2015JA021135 Chorus wave; Cyclotron resonance; Landau resonance; oblique whistler; wave generation |
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Very Oblique Whistler Generation By Low Energy Electron Streams Whistler-mode chorus waves are present throughout the Earth\textquoterights outer radiation belt as well as at larger distances from our planet. While the generation mechanisms of parallel lower-band chorus waves and oblique upper-band chorus waves have been identified and checked in various instances, the statistically significant presence in recent satellite observations of very oblique lower-band chorus waves near the resonance cone angle remains to be explained. Here we discuss two possible generation mechanisms for such waves. The first one is based on Landau resonance with sporadic very low energy (<4 keV) electron beams either injected from the plasmasheet or produced in situ. The second one relies on cyclotron resonance with low energy electron streams, such that their velocity distribution possesses both a significant temperature anisotropy above 3-4 keV and a plateau or heavy tail in parallel velocities at lower energies encompassing simultaneous Landau resonance with the same waves. The corresponding frequency and wave normal angle distributions of the generated very oblique lower-band chorus waves, as well as their frequency sweep rate, are evaluated analytically and compared with satellite observations, showing a reasonable agreement. Mourenas, D.; Artemyev, A.; Agapitov, O.; Krasnoselskikh, V.; Mozer, F.S.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2015JA021135 Chorus wave; Cyclotron resonance; Landau resonance; oblique whistler; wave generation |
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Very Oblique Whistler Generation By Low Energy Electron Streams Whistler-mode chorus waves are present throughout the Earth\textquoterights outer radiation belt as well as at larger distances from our planet. While the generation mechanisms of parallel lower-band chorus waves and oblique upper-band chorus waves have been identified and checked in various instances, the statistically significant presence in recent satellite observations of very oblique lower-band chorus waves near the resonance cone angle remains to be explained. Here we discuss two possible generation mechanisms for such waves. The first one is based on Landau resonance with sporadic very low energy (<4 keV) electron beams either injected from the plasmasheet or produced in situ. The second one relies on cyclotron resonance with low energy electron streams, such that their velocity distribution possesses both a significant temperature anisotropy above 3-4 keV and a plateau or heavy tail in parallel velocities at lower energies encompassing simultaneous Landau resonance with the same waves. The corresponding frequency and wave normal angle distributions of the generated very oblique lower-band chorus waves, as well as their frequency sweep rate, are evaluated analytically and compared with satellite observations, showing a reasonable agreement. Mourenas, D.; Artemyev, A.; Agapitov, O.; Krasnoselskikh, V.; Mozer, F.S.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2015JA021135 Chorus wave; Cyclotron resonance; Landau resonance; oblique whistler; wave generation |
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What frequencies of standing surface waves can the subsolar magnetopause support? It is has been proposed that the subsolar magnetopause may support its own eigenmode, consisting of propagating surface waves which reflect at the northern/southern ionospheres forming a standing wave. While the eigenfrequencies of these so-called Kruskal-Schwartzschild (KS) modes have been estimated under typical conditions, the potential distribution of frequencies over the full range of solar wind conditions is not know. Using models of the magnetosphere and magnetosheath applied to an entire solar cycle\textquoterights worth of solar wind data, we perform time-of-flight calculations yielding a database of KS mode frequencies. Under non-storm times or northward interplanetary magnetic field (IMF), the most likely fundamental frequency is calculated to be inline image mHz, consistent with previous estimates and indirect observational evidence for such standing surface waves of the subsolar magnetopause. However, the distributions exhibit significant spread (of order \textpm0.3 mHz) demonstrating that KS mode frequencies, especially higher harmonics, should vary considerably depending on the solar wind conditions. The implications of such large spread on observational statistics are discussed. The subsolar magnetopause eigenfrequencies are found to be most dependent on the solar wind speed, southward component of the IMF and the Dst index, with the latter two being due to the erosion of the magnetosphere by reconnection and the former an effect of the expression for the surface wave phase speed. Finally, the possible occurrence of KS modes is shown to be controlled by the dipole tilt angle. Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2014JA020545 |
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What frequencies of standing surface waves can the subsolar magnetopause support? It is has been proposed that the subsolar magnetopause may support its own eigenmode, consisting of propagating surface waves which reflect at the northern/southern ionospheres forming a standing wave. While the eigenfrequencies of these so-called Kruskal-Schwartzschild (KS) modes have been estimated under typical conditions, the potential distribution of frequencies over the full range of solar wind conditions is not know. Using models of the magnetosphere and magnetosheath applied to an entire solar cycle\textquoterights worth of solar wind data, we perform time-of-flight calculations yielding a database of KS mode frequencies. Under non-storm times or northward interplanetary magnetic field (IMF), the most likely fundamental frequency is calculated to be inline image mHz, consistent with previous estimates and indirect observational evidence for such standing surface waves of the subsolar magnetopause. However, the distributions exhibit significant spread (of order \textpm0.3 mHz) demonstrating that KS mode frequencies, especially higher harmonics, should vary considerably depending on the solar wind conditions. The implications of such large spread on observational statistics are discussed. The subsolar magnetopause eigenfrequencies are found to be most dependent on the solar wind speed, southward component of the IMF and the Dst index, with the latter two being due to the erosion of the magnetosphere by reconnection and the former an effect of the expression for the surface wave phase speed. Finally, the possible occurrence of KS modes is shown to be controlled by the dipole tilt angle. Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2014JA020545 |
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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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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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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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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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Local acceleration via whistler wave and particle interaction plays a significant role in particle dynamics in the radiation belt. In this work we explore gyroresonant wave-particle interaction and quasi-linear diffusion in different magnetic field configurations related to the 17 March 2013 storm. We consider the Earth\textquoterights magnetic dipole field as a reference and compare the results against nondipole field configurations corresponding to quiet and stormy conditions. The latter are obtained with the ring current-atmosphere interactions model with a self-consistent magnetic field (RAM-SCB), a code that models the Earth\textquoterights ring current and provides a realistic modeling of the Earth\textquoterights magnetic field. By applying quasi-linear theory, the bounce- and Magnetic Local Time (MLT)-averaged electron pitch angle, mixed-term, and energy diffusion coefficients are calculated for each magnetic field configuration. For radiation belt (\~1 MeV) and ring current (\~100 keV) electrons, it is shown that at some MLTs the bounce-averaged diffusion coefficients become rather insensitive to the details of the magnetic field configuration, while at other MLTs storm conditions can expand the range of equatorial pitch angles where gyroresonant diffusion occurs and significantly enhance the diffusion rates. When MLT average is performed at drift shell L=4.25 (a good approximation to drift average), the diffusion coefficients become quite independent of the magnetic field configuration for relativistic electrons, while the opposite is true for lower energy electrons. These results suggest that, at least for the 17 March 2013 storm and for L≲4.25, the commonly adopted dipole approximation of the Earth\textquoterights magnetic field can be safely used for radiation belt electrons, while a realistic modeling of the magnetic field configuration is necessary to describe adequately the diffusion rates of ring current electrons. Zhao, Lei; Yu, Yiqun; Delzanno, Gian; Jordanova, Vania; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2014JA020858 |
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Local acceleration via whistler wave and particle interaction plays a significant role in particle dynamics in the radiation belt. In this work we explore gyroresonant wave-particle interaction and quasi-linear diffusion in different magnetic field configurations related to the 17 March 2013 storm. We consider the Earth\textquoterights magnetic dipole field as a reference and compare the results against nondipole field configurations corresponding to quiet and stormy conditions. The latter are obtained with the ring current-atmosphere interactions model with a self-consistent magnetic field (RAM-SCB), a code that models the Earth\textquoterights ring current and provides a realistic modeling of the Earth\textquoterights magnetic field. By applying quasi-linear theory, the bounce- and Magnetic Local Time (MLT)-averaged electron pitch angle, mixed-term, and energy diffusion coefficients are calculated for each magnetic field configuration. For radiation belt (\~1 MeV) and ring current (\~100 keV) electrons, it is shown that at some MLTs the bounce-averaged diffusion coefficients become rather insensitive to the details of the magnetic field configuration, while at other MLTs storm conditions can expand the range of equatorial pitch angles where gyroresonant diffusion occurs and significantly enhance the diffusion rates. When MLT average is performed at drift shell L=4.25 (a good approximation to drift average), the diffusion coefficients become quite independent of the magnetic field configuration for relativistic electrons, while the opposite is true for lower energy electrons. These results suggest that, at least for the 17 March 2013 storm and for L≲4.25, the commonly adopted dipole approximation of the Earth\textquoterights magnetic field can be safely used for radiation belt electrons, while a realistic modeling of the magnetic field configuration is necessary to describe adequately the diffusion rates of ring current electrons. Zhao, Lei; Yu, Yiqun; Delzanno, Gian; Jordanova, Vania; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2014JA020858 |
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Local acceleration via whistler wave and particle interaction plays a significant role in particle dynamics in the radiation belt. In this work we explore gyroresonant wave-particle interaction and quasi-linear diffusion in different magnetic field configurations related to the 17 March 2013 storm. We consider the Earth\textquoterights magnetic dipole field as a reference and compare the results against nondipole field configurations corresponding to quiet and stormy conditions. The latter are obtained with the ring current-atmosphere interactions model with a self-consistent magnetic field (RAM-SCB), a code that models the Earth\textquoterights ring current and provides a realistic modeling of the Earth\textquoterights magnetic field. By applying quasi-linear theory, the bounce- and Magnetic Local Time (MLT)-averaged electron pitch angle, mixed-term, and energy diffusion coefficients are calculated for each magnetic field configuration. For radiation belt (\~1 MeV) and ring current (\~100 keV) electrons, it is shown that at some MLTs the bounce-averaged diffusion coefficients become rather insensitive to the details of the magnetic field configuration, while at other MLTs storm conditions can expand the range of equatorial pitch angles where gyroresonant diffusion occurs and significantly enhance the diffusion rates. When MLT average is performed at drift shell L=4.25 (a good approximation to drift average), the diffusion coefficients become quite independent of the magnetic field configuration for relativistic electrons, while the opposite is true for lower energy electrons. These results suggest that, at least for the 17 March 2013 storm and for L≲4.25, the commonly adopted dipole approximation of the Earth\textquoterights magnetic field can be safely used for radiation belt electrons, while a realistic modeling of the magnetic field configuration is necessary to describe adequately the diffusion rates of ring current electrons. Zhao, Lei; Yu, Yiqun; Delzanno, Gian; Jordanova, Vania; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2014JA020858 |
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Most previous work on nonlinear wave-particle interactions between energetic electrons and VLF waves in the Earth\textquoterights magnetosphere has assumed parallel propagation, the underlying mechanism being nonlinear trapping of cyclotron resonant electrons in a parabolic magnetic field inhomogeneity. Here nonlinear wave-particle interaction in oblique whistlers in the Earth\textquoterights magnetosphere is investigated. The study is nonself-consistent and assumes an arbitrarily chosen wave field. We employ a \textquotedblleftcontinuous wave\textquotedblright wave field with constant frequency and amplitude, and a model for an individual VLF chorus element. We derive the equations of motion and trapping conditions in oblique whistlers. The resonant particle distribution function, resonant current, and nonlinear growth rate are computed as functions of position and time. For all resonances of order n, resonant electrons obey the trapping equation, and provided the wave amplitude is big enough for the prevailing obliquity, nonlinearity manifests itself by a \textquotedbllefthole\textquotedblright or \textquotedbllefthill\textquotedblright in distribution function, depending on the zero-order distribution function and on position. A key finding is that the n = 1 resonance is relatively unaffected by moderate obliquity up to 25\textdegree, but growth rates roll off rapidly at high obliquity. The n = 1 resonance saturates due to the adiabatic effect and here reaches a maximum growth at ~20 pT, 2000 km from the equator. Damping due to the n = 0 resonance is not subject to adiabatic effects and maximizes at some 8000 km from the equator at an obliquity ~55\textdegree. Nunn, David; Omura, Yoshiharu; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2014JA020898 Chorus; nonlinear process; oblique propagation; simulation; Wave-particle interaction; whistler |
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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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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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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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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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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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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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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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Fast damping of ultralow frequency waves excited by interplanetary shocks in the magnetosphere Analysis of Cluster spacecraft data shows that intense ultralow frequency (ULF) waves in the inner magnetosphere can be excited by the impact of interplanetary shocks and solar wind dynamic pressure variations. The observations reveal that such waves can be damped away rapidly in a few tens of minutes. Here we examine mechanisms of ULF wave damping for two interplanetary shocks observed by Cluster on 7 November 2004 and 30 August 2001. The mechanisms considered are ionospheric joule heating, Landau damping, and waveguide energy propagation. It is shown that Landau damping provides the dominant ULF wave damping for the shock events of interest. It is further demonstrated that damping is caused by drift-bounce resonance with ions in the energy range of a few keV. Landau damping is shown to be more effective in the plasmasphere boundary layer due to the higher proportion of Landau resonant ions that exist in that region. Wang, Chengrui; Rankin, Robert; Zong, Qiugang; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2015 YEAR: 2015 DOI: 10.1002/2014JA020761 |
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Fast damping of ultralow frequency waves excited by interplanetary shocks in the magnetosphere Analysis of Cluster spacecraft data shows that intense ultralow frequency (ULF) waves in the inner magnetosphere can be excited by the impact of interplanetary shocks and solar wind dynamic pressure variations. The observations reveal that such waves can be damped away rapidly in a few tens of minutes. Here we examine mechanisms of ULF wave damping for two interplanetary shocks observed by Cluster on 7 November 2004 and 30 August 2001. The mechanisms considered are ionospheric joule heating, Landau damping, and waveguide energy propagation. It is shown that Landau damping provides the dominant ULF wave damping for the shock events of interest. It is further demonstrated that damping is caused by drift-bounce resonance with ions in the energy range of a few keV. Landau damping is shown to be more effective in the plasmasphere boundary layer due to the higher proportion of Landau resonant ions that exist in that region. Wang, Chengrui; Rankin, Robert; Zong, Qiugang; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2015 YEAR: 2015 DOI: 10.1002/2014JA020761 |
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Global Storm-Time Depletion of the Outer Electron Belt The outer radiation belt consists of relativistic (>0.5 MeV) electrons trapped on closed trajectories around Earth where the magnetic field is nearly dipolar. During increased geomagnetic activity, electron intensities in the belt can vary by ordersof magnitude at different spatial and temporal scale. The main phase of geomagnetic storms often produces deep depletions of electron intensities over broad regions of the outer belt. Previous studies identified three possible processes that can contribute to the main-phase depletions: adiabatic inflation of electron drift orbits caused by the ring current growth, electron loss into the atmosphere, and electron escape through the magnetopause boundary. In this paper we investigate the relative importance of the adiabatic effect and magnetopause loss to the rapid depletion of the outer belt observed at the Van Allen Probes spacecraft during the main phase of March 17, 2013 storm. The intensities of >1 MeV electrons were depleted by more than an order of magnitude over the entire radial extent of the belt in less than 6 hours after the sudden storm commencement. For the analysis we used three-dimensional test-particle simulations of global evolution of the outer belt in the Tsyganenko-Sitnov (TS07D) magnetic field model with an inductive electric field. Comparison of the simulation results with electron measurements from the MagEIS experiment shows that magnetopause loss accounts for most of the observed depletion at L>5, while at lower L shells the depletion is adiabatic. Both magnetopause loss and the adiabatic effect are controlled by the change in global configuration of the magnetic field due to storm-time development of the ring current; a simulation of electron evolution without a ring current produces a much weaker depletion. Ukhorskiy, A; Sitnov, M.; Millan, R.; Kress, B.; Fennell, J.; Claudepierre, S.; Barnes, R.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2015 YEAR: 2015 DOI: 10.1002/2014JA020645 dropout; Geomagnetic storms; magnetopause loss; Radial Transport; Radiation belt; ring current; Van Allen Probes |
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Global Storm-Time Depletion of the Outer Electron Belt The outer radiation belt consists of relativistic (>0.5 MeV) electrons trapped on closed trajectories around Earth where the magnetic field is nearly dipolar. During increased geomagnetic activity, electron intensities in the belt can vary by ordersof magnitude at different spatial and temporal scale. The main phase of geomagnetic storms often produces deep depletions of electron intensities over broad regions of the outer belt. Previous studies identified three possible processes that can contribute to the main-phase depletions: adiabatic inflation of electron drift orbits caused by the ring current growth, electron loss into the atmosphere, and electron escape through the magnetopause boundary. In this paper we investigate the relative importance of the adiabatic effect and magnetopause loss to the rapid depletion of the outer belt observed at the Van Allen Probes spacecraft during the main phase of March 17, 2013 storm. The intensities of >1 MeV electrons were depleted by more than an order of magnitude over the entire radial extent of the belt in less than 6 hours after the sudden storm commencement. For the analysis we used three-dimensional test-particle simulations of global evolution of the outer belt in the Tsyganenko-Sitnov (TS07D) magnetic field model with an inductive electric field. Comparison of the simulation results with electron measurements from the MagEIS experiment shows that magnetopause loss accounts for most of the observed depletion at L>5, while at lower L shells the depletion is adiabatic. Both magnetopause loss and the adiabatic effect are controlled by the change in global configuration of the magnetic field due to storm-time development of the ring current; a simulation of electron evolution without a ring current produces a much weaker depletion. Ukhorskiy, A; Sitnov, M.; Millan, R.; Kress, B.; Fennell, J.; Claudepierre, S.; Barnes, R.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2015 YEAR: 2015 DOI: 10.1002/2014JA020645 dropout; Geomagnetic storms; magnetopause loss; Radial Transport; Radiation belt; ring current; Van Allen Probes |
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Global Storm-Time Depletion of the Outer Electron Belt The outer radiation belt consists of relativistic (>0.5 MeV) electrons trapped on closed trajectories around Earth where the magnetic field is nearly dipolar. During increased geomagnetic activity, electron intensities in the belt can vary by ordersof magnitude at different spatial and temporal scale. The main phase of geomagnetic storms often produces deep depletions of electron intensities over broad regions of the outer belt. Previous studies identified three possible processes that can contribute to the main-phase depletions: adiabatic inflation of electron drift orbits caused by the ring current growth, electron loss into the atmosphere, and electron escape through the magnetopause boundary. In this paper we investigate the relative importance of the adiabatic effect and magnetopause loss to the rapid depletion of the outer belt observed at the Van Allen Probes spacecraft during the main phase of March 17, 2013 storm. The intensities of >1 MeV electrons were depleted by more than an order of magnitude over the entire radial extent of the belt in less than 6 hours after the sudden storm commencement. For the analysis we used three-dimensional test-particle simulations of global evolution of the outer belt in the Tsyganenko-Sitnov (TS07D) magnetic field model with an inductive electric field. Comparison of the simulation results with electron measurements from the MagEIS experiment shows that magnetopause loss accounts for most of the observed depletion at L>5, while at lower L shells the depletion is adiabatic. Both magnetopause loss and the adiabatic effect are controlled by the change in global configuration of the magnetic field due to storm-time development of the ring current; a simulation of electron evolution without a ring current produces a much weaker depletion. Ukhorskiy, A; Sitnov, M.; Millan, R.; Kress, B.; Fennell, J.; Claudepierre, S.; Barnes, R.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2015 YEAR: 2015 DOI: 10.1002/2014JA020645 dropout; Geomagnetic storms; magnetopause loss; Radial Transport; Radiation belt; ring current; Van Allen Probes |
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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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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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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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We analyze observations of subionospherically propagating very low frequency (VLF) radio waves to determine outer radiation belt energetic electron precipitation (EEP) flux magnitudes. The radio wave receiver in Sodankylä, Finland (Sodankylä Geophysical Observatory) observes signals from the transmitter with call sign NAA (Cutler, Maine). The receiver is part of the Antarctic-Arctic Radiation-belt Dynamic Deposition VLF Atmospheric Research Konsortia (AARDDVARK). We use a near-continuous data set spanning November 2004 until December 2013 to determine the long time period EEP variations. We determine quiet day curves over the entire period and use these to identify propagation disturbances caused by EEP. Long Wave Propagation Code radio wave propagation modeling is used to estimate the precipitating electron flux magnitudes from the observed amplitude disturbances, allowing for solar cycle changes in the ambient D region and dynamic variations in the EEP energy spectra. Our method performs well during the summer months when the daylit ionosphere is most stable but fails during the winter. From the summer observations, we have obtained 693 days worth of hourly EEP flux magnitudes over the 2004\textendash2013 period. These AARDDVARK-based fluxes agree well with independent satellite precipitation measurements during high-intensity events. However, our method of EEP detection is 10\textendash50 times more sensitive to low flux levels than the satellite measurements. Our EEP variations also show good agreement with the variation in lower band chorus wave powers, providing some confidence that chorus is the primary driver for the outer belt precipitation we are monitoring. Neal, Jason; Rodger, Craig; Clilverd, Mark; Thomson, Neil; Raita, Tero; Ulich, Thomas; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2015 YEAR: 2015 DOI: 10.1002/2014JA020689 AARDDVARK network; electron precipitation; Radiation belts; subionospheric VLF propagation |
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We analyze observations of subionospherically propagating very low frequency (VLF) radio waves to determine outer radiation belt energetic electron precipitation (EEP) flux magnitudes. The radio wave receiver in Sodankylä, Finland (Sodankylä Geophysical Observatory) observes signals from the transmitter with call sign NAA (Cutler, Maine). The receiver is part of the Antarctic-Arctic Radiation-belt Dynamic Deposition VLF Atmospheric Research Konsortia (AARDDVARK). We use a near-continuous data set spanning November 2004 until December 2013 to determine the long time period EEP variations. We determine quiet day curves over the entire period and use these to identify propagation disturbances caused by EEP. Long Wave Propagation Code radio wave propagation modeling is used to estimate the precipitating electron flux magnitudes from the observed amplitude disturbances, allowing for solar cycle changes in the ambient D region and dynamic variations in the EEP energy spectra. Our method performs well during the summer months when the daylit ionosphere is most stable but fails during the winter. From the summer observations, we have obtained 693 days worth of hourly EEP flux magnitudes over the 2004\textendash2013 period. These AARDDVARK-based fluxes agree well with independent satellite precipitation measurements during high-intensity events. However, our method of EEP detection is 10\textendash50 times more sensitive to low flux levels than the satellite measurements. Our EEP variations also show good agreement with the variation in lower band chorus wave powers, providing some confidence that chorus is the primary driver for the outer belt precipitation we are monitoring. Neal, Jason; Rodger, Craig; Clilverd, Mark; Thomson, Neil; Raita, Tero; Ulich, Thomas; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2015 YEAR: 2015 DOI: 10.1002/2014JA020689 AARDDVARK network; electron precipitation; Radiation belts; subionospheric VLF propagation |
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Postmidnight depletion of the high-energy tail of the quiet plasmasphere The Van Allen Probes Helium Oxygen Proton Electron (HOPE) instrument measures the high-energy tail of the thermal plasmasphere allowing study of topside ionosphere and inner magnetosphere coupling. We statistically analyze a 22 month period of HOPE data, looking at quiet times with a Kp index of less than 3. We investigate the high-energy range of the plasmasphere, which consists of ions at energies between 1 and 10 eV and contains approximately 5\% of total plasmaspheric density. Both the fluxes and partial plasma densities over this energy range show H+ is depleted the most in the postmidnight sector (1\textendash4 magnetic local time), followed by O+ and then He+. The relative depletion of each species across the postmidnight sector is not ordered by mass, which reveals ionospheric influence. We compare our results with keV energy electron data from HOPE and the Van Allen Probes Electric Fields and Waves instrument spacecraft potential to rule out spacecraft charging. Our conclusion is that the postmidnight ion disappearance is due to diurnal ionospheric temperature variation and charge exchange processes. Sarno-Smith, Lois; Liemohn, Michael; Katus, Roxanne; Skoug, Ruth; Larsen, Brian; Thomsen, Michelle; Wygant, John; Moldwin, Mark; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2015 YEAR: 2015 DOI: 10.1002/2014JA020682 ion composition; Ionosphere; plasmasphere; postmidnight; quiet time magnetosphere; Van Allen Probes |