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Found 1116 entries in the Bibliography.
Showing entries from 651 through 700
| 2016 |
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Analysis of particle pitch angle distributions (PADs) has been used as a means to comprehend a multitude of different physical mechanisms that lead to flux variations in the Van Allen belts and also to particle precipitation into the upper atmosphere. In this work we developed a neural network-based data clustering methodology that automatically identifies distinct PAD types in an unsupervised way using particle flux data. One can promptly identify and locate three well-known PAD types in both time and radial distance, namely, 90\textdegree peaked, butterfly, and flattop distributions. In order to illustrate the applicability of our methodology, we used relativistic electron flux data from the whole month of November 2014, acquired from the Relativistic Electron-Proton Telescope instrument on board the Van Allen Probes, but it is emphasized that our approach can also be used with multiplatform spacecraft data. Our PAD classification results are in reasonably good agreement with those obtained by standard statistical fitting algorithms. The proposed methodology has a potential use for Van Allen belt\textquoterights monitoring. Souza, V.; Vieira, L.; Medeiros, C.; Da Silva, L.; Alves, L.; Koga, D.; Sibeck, D.; Walsh, B.; Kanekal, S.; Jauer, P.; Rockenbach, M.; Dal Lago, A.; Silveira, M.; Marchezi, J.; Mendes, O.; Gonzalez, W.; Baker, D.; Published by: Space Weather Published on: 04/2016 YEAR: 2016 DOI: 10.1002/2015SW001349 pitch angle distributions; self-organizing maps; Van Allen belt\textquoterights monitoring; Van Allen Probes |
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Ring current electron dynamics during geomagnetic storms based on the Van Allen Probes measurements Based on comprehensive measurements from Helium, Oxygen, Proton, and Electron Mass Spectrometer Ion Spectrometer, Relativistic Electron-Proton Telescope, and Radiation Belt Storm Probes Ion Composition Experiment instruments on the Van Allen Probes, comparative studies of ring current electrons and ions are performed and the role of energetic electrons in the ring current dynamics is investigated. The deep injections of tens to hundreds of keV electrons and tens of keV protons into the inner magnetosphere occur frequently; after the injections the electrons decay slowly in the inner belt but protons in the low L region decay very fast. Intriguing similarities between lower energy protons and higher-energy electrons are also found. The evolution of ring current electron and ion energy densities and energy content are examined in detail during two geomagnetic storms, one moderate and one intense. The results show that the contribution of ring current electrons to the ring current energy content is much smaller than that of ring current ions (up to ~12\% for the moderate storm and ~7\% for the intense storm), and <35 keV electrons dominate the ring current electron energy content at the storm main phases. Though the electron energy content is usually much smaller than that of ions, the enhancement of ring current electron energy content during the moderate storm can get to ~30\% of that of ring current ions, indicating a more dynamic feature of ring current electrons and important role of electrons in the ring current buildup. The ring current electron energy density is also shown to be higher at midnight and dawn while lower at noon and dusk. Zhao, H.; Li, X.; Baker, D.; Claudepierre, S.; Fennell, J.; Blake, J.; Larsen, B.; Skoug, R.; Funsten, H.; Friedel, R.; Reeves, G.; Spence, H.; Mitchell, D.; Lanzerotti, L.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2016 YEAR: 2016 DOI: 10.1002/2016JA022358 deep injections; Geomagnetic storms; ring current; ring current energy content; ring current electrons; Van Allen Probes |
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Ring current electron dynamics during geomagnetic storms based on the Van Allen Probes measurements Based on comprehensive measurements from Helium, Oxygen, Proton, and Electron Mass Spectrometer Ion Spectrometer, Relativistic Electron-Proton Telescope, and Radiation Belt Storm Probes Ion Composition Experiment instruments on the Van Allen Probes, comparative studies of ring current electrons and ions are performed and the role of energetic electrons in the ring current dynamics is investigated. The deep injections of tens to hundreds of keV electrons and tens of keV protons into the inner magnetosphere occur frequently; after the injections the electrons decay slowly in the inner belt but protons in the low L region decay very fast. Intriguing similarities between lower energy protons and higher-energy electrons are also found. The evolution of ring current electron and ion energy densities and energy content are examined in detail during two geomagnetic storms, one moderate and one intense. The results show that the contribution of ring current electrons to the ring current energy content is much smaller than that of ring current ions (up to ~12\% for the moderate storm and ~7\% for the intense storm), and <35 keV electrons dominate the ring current electron energy content at the storm main phases. Though the electron energy content is usually much smaller than that of ions, the enhancement of ring current electron energy content during the moderate storm can get to ~30\% of that of ring current ions, indicating a more dynamic feature of ring current electrons and important role of electrons in the ring current buildup. The ring current electron energy density is also shown to be higher at midnight and dawn while lower at noon and dusk. Zhao, H.; Li, X.; Baker, D.; Claudepierre, S.; Fennell, J.; Blake, J.; Larsen, B.; Skoug, R.; Funsten, H.; Friedel, R.; Reeves, G.; Spence, H.; Mitchell, D.; Lanzerotti, L.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2016 YEAR: 2016 DOI: 10.1002/2016JA022358 deep injections; Geomagnetic storms; ring current; ring current energy content; ring current electrons; Van Allen Probes |
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Ring current electron dynamics during geomagnetic storms based on the Van Allen Probes measurements Based on comprehensive measurements from Helium, Oxygen, Proton, and Electron Mass Spectrometer Ion Spectrometer, Relativistic Electron-Proton Telescope, and Radiation Belt Storm Probes Ion Composition Experiment instruments on the Van Allen Probes, comparative studies of ring current electrons and ions are performed and the role of energetic electrons in the ring current dynamics is investigated. The deep injections of tens to hundreds of keV electrons and tens of keV protons into the inner magnetosphere occur frequently; after the injections the electrons decay slowly in the inner belt but protons in the low L region decay very fast. Intriguing similarities between lower energy protons and higher-energy electrons are also found. The evolution of ring current electron and ion energy densities and energy content are examined in detail during two geomagnetic storms, one moderate and one intense. The results show that the contribution of ring current electrons to the ring current energy content is much smaller than that of ring current ions (up to ~12\% for the moderate storm and ~7\% for the intense storm), and <35 keV electrons dominate the ring current electron energy content at the storm main phases. Though the electron energy content is usually much smaller than that of ions, the enhancement of ring current electron energy content during the moderate storm can get to ~30\% of that of ring current ions, indicating a more dynamic feature of ring current electrons and important role of electrons in the ring current buildup. The ring current electron energy density is also shown to be higher at midnight and dawn while lower at noon and dusk. Zhao, H.; Li, X.; Baker, D.; Claudepierre, S.; Fennell, J.; Blake, J.; Larsen, B.; Skoug, R.; Funsten, H.; Friedel, R.; Reeves, G.; Spence, H.; Mitchell, D.; Lanzerotti, L.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2016 YEAR: 2016 DOI: 10.1002/2016JA022358 deep injections; Geomagnetic storms; ring current; ring current energy content; ring current electrons; Van Allen Probes |
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The Van Allen Probe observations during the recovery phase of a large storm that occurred on 17 March 2015 showed that the ultrarelativistic electrons at the inner boundary of the outer radiation belt (L* = 2.6\textendash3.7) exhibited butterfly pitch angle distributions, while the inner belt and the slot region also showed evidence of sub-MeV electron butterfly distributions. Strong magnetosonic waves were observed in the same regions and at the same time periods as these butterfly distributions. Moreover, when these magnetosonic waves extended to higher altitudes (L* = 4.1), the butterfly distributions also extended to the same region. Combining test particle calculations and Fokker-Planck diffusion simulations, we successfully reproduced the formation of the ultrarelativistic electron butterfly distributions, which primarily result from parallel acceleration caused by Landau resonance with magnetosonic waves. The coexistence of ultrarelativistic electron butterfly distributions with magnetosonic waves was also observed in the 24 June 2015 storm, providing further support that the magnetosonic waves play a key role in forming butterfly distributions. Li, Jinxing; Bortnik, Jacob; Thorne, Richard; Li, Wen; Ma, Qianli; Baker, Daniel; Reeves, Geoffrey; Fennell, Joseph; Spence, Harlan; Kletzing, Craig; Kurth, William; Hospodarsky, George; Angelopoulos, Vassilis; Blake, Bernard.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2016 YEAR: 2016 DOI: 10.1002/2016JA022370 butterfly distributions; Landau resonance; magnetosonic waves; Radiation belt; Van Allen Probes |
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Ultralow frequency (ULF) electromagnetic waves in Earth\textquoterights magnetosphere can accelerate charged particles via a process called drift resonance. In the conventional drift-resonance theory, a default assumption is that the wave growth rate is time-independent, positive, and extremely small. However, this is not the case for ULF waves in the real magnetosphere. The ULF waves must have experienced an earlier growth stage when their energy was taken from external and/or internal sources, and as time proceeds the waves have to be damped with a negative growth rate. Therefore, a more generalized theory on particle behavior during different stages of ULF wave evolution is required. In this paper, we introduce a time-dependent imaginary wave frequency to accommodate the growth and damping of the waves in the drift-resonance theory, so that the wave-particle interactions during the entire wave lifespan can be studied. We then predict from the generalized theory particle signatures during different stages of the wave evolution, which are consistent with observations from Van Allen Probes. The more generalized theory, therefore, provides new insights into ULF wave evolution and wave-particle interactions in the magnetosphere. Zhou, Xu-Zhi; Wang, Zi-Han; Zong, Qiu-Gang; Rankin, Robert; Kivelson, Margaret; Chen, Xing-Ran; Blake, Bernard; Wygant, John; Kletzing, Craig; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2016 YEAR: 2016 DOI: 10.1002/2016JA022447 drift resonance; Radiation belt; ULF waves; Van Allen Probes; wave growth and damping; Wave-particle interaction |
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Inward diffusion and loss of radiation belt protons Radiation belt protons in the kinetic energy range 24 to 76 MeV are being measured by the Relativistic Electron Proton Telescope on each of the two Van Allen Probes. Data have been processed for the purpose of studying variability in the trapped proton intensity during October 2013 to August 2015. For the lower energies (≲32 MeV), equatorial proton intensity near L = 2 showed a steady increase that is consistent with inward diffusion of trapped solar protons, as shown by positive radial gradients in phase space density at fixed values of the first two adiabatic invariants. It is postulated that these protons were trapped with enhanced efficiency during the 7 March 2012 solar proton event. A model that includes radial diffusion, along with known trapped proton source and loss processes, shows that the observed average rate of increase near L = 2 is predicted by the same model diffusion coefficient that is required to form the entire proton radiation belt, down to low L, over an extended (\~103 year) interval. A slower intensity decrease for lower energies near L = 1.5 may also be caused by inward diffusion, though it is faster than predicted by the model. Higher-energy (≳40 MeV) protons near the L = 1.5 intensity maximum are from cosmic ray albedo neutron decay. Their observed intensity is lower than expected by a factor \~2, but the discrepancy is resolved by adding an unspecified loss process to the model with a mean lifetime \~120 years. Selesnick, R.; Baker, D.; Jaynes, A.; Li, X.; Kanekal, S.; Hudson, M.; Kress, B.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2016 YEAR: 2016 DOI: 10.1002/2015JA022154 |
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Lightning-generated whistler waves are electromagnetic plasma waves in the very low frequency (VLF) band, which play an important role in the dynamics of radiation belt particles. In this paper, we statistically analyze simultaneous waveform data from the Van Allen Probes (Radiation Belt Storm Probes, RBSP) and global lightning data from the World Wide Lightning Location Network (WWLLN). Data were obtained between July to September 2013 and between March and April 2014. For each day during these periods, we predicted the most probable 10 min for which each of the two RBSP satellites would be magnetically conjugate to lightning producing regions. The prediction method uses integrated WWLLN stroke data for that day obtained during the three previous years. Using these predicted times for magnetic conjugacy to lightning activity regions, we recorded high time resolution, burst mode waveform data. Here we show that whistlers are observed by the satellites in more than 80\% of downloaded waveform data. About 22.9\% of the whistlers observed by RBSP are one-to-one coincident with source lightning strokes detected by WWLLN. About 40.1\% more of whistlers are found to be one-to-one coincident with lightning if source regions are extended out 2000 km from the satellites footpoints. Lightning strokes with far-field radiated VLF energy larger than about 100 J are able to generate a detectable whistler wave in the inner magnetosphere. One-to-one coincidences between whistlers observed by RBSP and lightning strokes detected by WWLLN are clearly shown in the L shell range of L = 1\textendash3. Nose whistlers observed in July 2014 show that it may be possible to extend this coincidence to the region of L>=4. Zheng, Hao; Holzworth, Robert; Brundell, James; Jacobson, Abram; Wygant, John; Hospodarsky, George; Mozer, Forrest; Bonnell, John; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2016 YEAR: 2016 DOI: 10.1002/2015JA022010 |
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Our investigation of the long-term ring current proton pressure evolution in Earth\textquoterights inner magnetosphere based on Van Allen Probes data shows drastically different behavior of the low- and high- energy components of the ring current proton population with respect to the Sym-H index variation. We found that while the low-energy component of the protons (<80 keV) is strongly governed by convective timescales and is very well correlated with the absolute value of Sym-H index, the high-energy component (>100 keV) varies on much longer timescales and shows either no or anti-correlation with the absolute value of Sym-H index. Our study also shows that the contributions of the low- and high- energy protons to the inner magnetosphere energy content are comparable. Thus, our results conclusively demonstrate that proton dynamics, and as a result the energy budget in the inner magnetosphere, do not vary strictly on storm-time timescales as those are defined by the Sym-H index. Gkioulidou, Matina; Ukhorskiy, A.; Mitchell, D.; Lanzerotti, L.; Published by: Geophysical Research Letters Published on: 03/2016 YEAR: 2016 DOI: 10.1002/2016GL068013 energy budget; Geomagnetic storms; inner magnetosphere; ring current; Van Allen Probes |
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A case study of shortwave radar observations of magnetospheric Pc5 ULF waves (wave periods of 150\textendash600 s) that occurred on 26 December 2014 in the nightside magnetosphere during substorm activity is presented. The radar study of waves in the magnetosphere is based on analysis of scattering from field-aligned irregularities of the ionospheric F layer. Variations of their inline image drift velocity at F layer heights are associated with the wave electric field. Analysis of the observations from the Ekaterinburg (EKB) radar shows that the frequency f of the observed wave depends on the azimuthal wave number m (positive correlation of about 0.90): an increase in frequency from 2.5 to 5 mHz corresponds to increased m number from 20 to 80. Of the known types of waves in the magnetosphere corresponding to the Pc5 range, only drift compressional waves have such azimuthal dispersion: the frequency of the drift compressional mode is directly proportional to the azimuthal wave number and the gradient-curvature drift velocity of energetic particles in the magnetic field. This wave has a kinetic nature and represents the most common kind of the compressional modes, demanding for its existence only finite pressure and plasma inhomogeneity across magnetic shells. Chelpanov, Maksim; Mager, Pavel; Klimushkin, Dmitri; Berngardt, Oleg; Mager, Olga; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2016 YEAR: 2016 DOI: 10.1002/2015JA022155 |
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Forecasting and remote sensing outer belt relativistic electrons from low Earth orbit This study demonstrates the feasibility and reliability of using observations from low Earth orbit (LEO) to forecast and nowcast relativistic electrons in the outer radiation belt. We first report a high cross-energy, cross-pitch-angle coherence discovered between the trapped MeV electrons and precipitating approximately hundreds (~100s) of keV electrons\textemdashobserved by satellites with very different altitudes\textemdashwith correlation coefficients as high as ≳ 0.85. Based upon the coherence, we then tested the feasibility of applying linear prediction filters to LEO data to predict the arrival of new MeV electrons during geomagnetic storms, as well as their evolving distributions afterward. Reliability of these predictive filters is quantified by the performance efficiency with values as high as 0.74 when driven merely by LEO observations (or up to 0.94 with the inclusion of in situ MeV electron measurements). Finally, a hypothesis based upon the wave-particle resonance theory is proposed to explain the coherence, and a first-principle electron tracing model yields supporting evidence. Chen, Yue; Reeves, Geoffrey; Cunningham, Gregory; Redmon, Robert; Henderson, Michael; Published by: Geophysical Research Letters Published on: 02/2016 YEAR: 2016 DOI: 10.1002/2015GL067481 forecast and nowcast; hundreds of keV precipitating electrons; LEO observations; Radiation belts; relativistic electrons; wave particle interactions |
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Forecasting and remote sensing outer belt relativistic electrons from low Earth orbit This study demonstrates the feasibility and reliability of using observations from low Earth orbit (LEO) to forecast and nowcast relativistic electrons in the outer radiation belt. We first report a high cross-energy, cross-pitch-angle coherence discovered between the trapped MeV electrons and precipitating approximately hundreds (~100s) of keV electrons\textemdashobserved by satellites with very different altitudes\textemdashwith correlation coefficients as high as ≳ 0.85. Based upon the coherence, we then tested the feasibility of applying linear prediction filters to LEO data to predict the arrival of new MeV electrons during geomagnetic storms, as well as their evolving distributions afterward. Reliability of these predictive filters is quantified by the performance efficiency with values as high as 0.74 when driven merely by LEO observations (or up to 0.94 with the inclusion of in situ MeV electron measurements). Finally, a hypothesis based upon the wave-particle resonance theory is proposed to explain the coherence, and a first-principle electron tracing model yields supporting evidence. Chen, Yue; Reeves, Geoffrey; Cunningham, Gregory; Redmon, Robert; Henderson, Michael; Published by: Geophysical Research Letters Published on: 02/2016 YEAR: 2016 DOI: 10.1002/2015GL067481 forecast and nowcast; hundreds of keV precipitating electrons; LEO observations; Radiation belts; relativistic electrons; wave particle interactions |
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New global loss model of energetic and relativistic electrons based on Van Allen Probes measurements Energetic electron observations in Earth\textquoterights radiation belts are typically sparse and multi-point studies often rely on serendipitous conjunctions. This paper establishes the scientific utility of the Combined X-ray Dosimeter (CXD), currently flown on 19 satellites in the Global Positioning System (GPS) constellation, by cross-calibrating energetic electron measurements against data from the Van Allen Probes. By breaking our cross-calibration into two parts \textendash one that removes any spectral assumptions from the CXD flux calculation, and one that compares the energy spectra \textendash we first validate the modeled instrument response functions, then the calculated electron fluxes. Unlike previous forward modeling of energetic electron spectra we use a combination of four distributions that, together, capture a wide range of observed spectral shapes. Our two-step approach allowed us to identify, and correct for, small systematic offsets between block IIR and IIF satellites. Using the Magnetic Electron Ion Spectrometer (MagEIS) and Relativistic Electron-Proton Telescope (REPT) on Van Allen Probes as a \textquotedblleftgold standard\textquotedblright we demonstrate that the CXD instruments are well-understood. A robust statistical analysis shows that CXD and Van Allen Probes fluxes are similar and the measured fluxes from CXD are typically within a factor of 2 of Van Allen Probes at energies ≲4 MeV. We present data from 17 CXD-equipped GPS satellites covering the 2015 \textquotedblleftSt. Patrick\textquoterights Day\textquotedblright geomagnetic storm to illustrate the scientific applications of such a high data density satellite constellation, and therefore demonstrate that the GPS constellation is positioned to enable new insights in inner magnetospheric physics and space weather forecasting. Orlova, Ksenia; Shprits, Yuri; Spasojevic, Maria; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2016 YEAR: 2016 DOI: 10.1002/2015JA021878 |
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Pulsating proton aurora caused by rising tone Pc1 waves We found rising tone emissions with a dispersion of \~1 Hz per several tens of seconds in the dynamic spectrum of a Pc1 geomagnetic pulsation (Pc1) observed on the ground. These Pc1 rising tones were successively observed over \~30 min from 0250 UT on 14 October 2006 by an induction magnetometer at Athabasca, Canada (54.7\textdegreeN, 246.7\textdegreeE, magnetic latitude 61.7\textdegreeN). Simultaneously, a Time History of Events and Macroscale Interactions during Substorms panchromatic (THEMIS) all-sky camera detected pulsations of an isolated proton aurora with a period of several tens of seconds, \~10\% variations in intensity, and fine structures of 3\textdegree in magnetic longitudes. The pulsations of the proton aurora close to the zenith of ATH have one-to-one correspondences with the Pc1 rising tones. This suggests that these rising tones scatter magnetospheric protons intermittently at the equatorial region. The radial motion of the magnetospheric source, of which the isolated proton aurora is a projection, can explain the central frequency increase of Pc1, but not the shorter period (tens of seconds) frequency increase of \~1 Hz in Pc1 rising tones. We suggest that EMIC-triggered emissions generate the frequency increase of Pc1 rising tones on the ground and that they also cause the Pc1 pearl structure, which has a similar characteristic time. Nomura, R.; Shiokawa, K.; Omura, Y.; Ebihara, Y.; Miyoshi, Y.; Sakaguchi, K.; Otsuka, Y.; Connors, M.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2016 YEAR: 2016 DOI: 10.1002/2015JA021681 |
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Pulsating proton aurora caused by rising tone Pc1 waves We found rising tone emissions with a dispersion of \~1 Hz per several tens of seconds in the dynamic spectrum of a Pc1 geomagnetic pulsation (Pc1) observed on the ground. These Pc1 rising tones were successively observed over \~30 min from 0250 UT on 14 October 2006 by an induction magnetometer at Athabasca, Canada (54.7\textdegreeN, 246.7\textdegreeE, magnetic latitude 61.7\textdegreeN). Simultaneously, a Time History of Events and Macroscale Interactions during Substorms panchromatic (THEMIS) all-sky camera detected pulsations of an isolated proton aurora with a period of several tens of seconds, \~10\% variations in intensity, and fine structures of 3\textdegree in magnetic longitudes. The pulsations of the proton aurora close to the zenith of ATH have one-to-one correspondences with the Pc1 rising tones. This suggests that these rising tones scatter magnetospheric protons intermittently at the equatorial region. The radial motion of the magnetospheric source, of which the isolated proton aurora is a projection, can explain the central frequency increase of Pc1, but not the shorter period (tens of seconds) frequency increase of \~1 Hz in Pc1 rising tones. We suggest that EMIC-triggered emissions generate the frequency increase of Pc1 rising tones on the ground and that they also cause the Pc1 pearl structure, which has a similar characteristic time. Nomura, R.; Shiokawa, K.; Omura, Y.; Ebihara, Y.; Miyoshi, Y.; Sakaguchi, K.; Otsuka, Y.; Connors, M.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2016 YEAR: 2016 DOI: 10.1002/2015JA021681 |
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We present a statistical survey of the latitudinal structure of the fast magnetosonic wave mode detected by the Van Allen Probes spanning the time interval of 9/21/2012 to 8/1/2014. We show that statistically the latitudinal occurrence of the wave frequency (f) normalized by the local proton cyclotron frequency (fcP) has a distinct funnel shaped appearance in latitude about the magnetic equator similar to that found in case studies. By comparing the observed E/B ratios with the model E/B ratio, using the observed plasma density and background magnetic field magnitude as input to the model E/B ratio, we show that this mode is consistent with the extraordinary (whistler) mode at wave normal angles (θk) near 90\textdegree. Performing polarization analysis on synthetic waveforms composed from a superposition of extra-ordinary mode plane waves with θk randomly chosen between 87 and 90\textdegree, we show that the uncertainty in the derived wave normal is substantially broadened, with a tail extending down to θk of 60\textdegree, suggesting that another approach is necessary to estimate the true distribution of θk. We find that the histograms of the synthetically derived ellipticities and θk are consistent with the observations of ellipticities and θk derived using polarization analysis. We make estimates of the median equatorial θk by comparing observed and model ray tracing frequency dependent probability occurrence with latitude, and give preliminary frequency dependent estimates of the equatorial θk distribution around noon and 4 RE, with the median of ~4 to 7\textdegree from 90\textdegree at f /fcP = 2 and dropping to ~0.5\textdegree from 90\textdegree at f /fcP = 30. The occurrence of waves in this mode peaks around noon near the equator at all radial distances, and we find that the overall intensity of these waves increases with AE*, similar to findings of other studies. Boardsen, Scott; Hospodarsky, George; Kletzing, Craig; Engebretson, Mark; Pfaff, Robert; Wygant, John; Kurth, William; Averkamp, Terrance; Bounds, Scott; Green, Jim; De Pascuale, Sebastian; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2016 YEAR: 2016 DOI: 10.1002/2015JA021844 EMFISIS; Fast Magnetosonic Waves; latitudinal distribution; statistical study; Van Allen Probes; wave normal angle |
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Determination of the Earth\textquoterights plasmapause location from the CE-3 EUVC images The Moon-based Extreme Ultraviolet Camera (EUVC) aboard China\textquoterights Chang\textquoterighte-3 (CE-3) mission has successfully imaged the entire Earth\textquoterights plasmasphere for the first time from the side views on lunar surface. An EUVC image on 21 April 2014 is used in this study to demonstrate the characteristics and configurations of the Moon-based EUV imaging and to illustrate the determination algorithm of the plasmapause locations on the magnetic equator. The plasmapause locations determined from all the available EUVC images with the Minimum L Algorithm are quantitatively compared with those extracted from in situ observations (Defense Meteorological Satellite Program, Time History of Events and Macroscale Interactions during Substorms, and Radiation Belt Storm Probes). Excellent agreement between the determined plasmapauses seen by EUVC and the extracted ones from other satellites indicates the reliability of the Moon-based EUVC images as well as the determination algorithm. This preliminary study provides an important basis for future investigation of the dynamics of the plasmasphere with the Moon-based EUVC imaging. He, Fei; Zhang, Xiao-Xin; Chen, Bo; Fok, Mei-Ching; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2016 YEAR: 2016 DOI: 10.1002/2015JA021863 Chang\textquoterighte-3; EUV imaging; Plasmapause; plasmasphere; reconstruction |
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Dipolarizing flux bundles (DFBs) are small flux tubes (typically < 3 RE in XGSM and YGSM) in the nightside magnetosphere that have magnetic field more dipolar than the background. Although DFBs are known to accelerate particles, creating energetic particle injections outside geosynchronous orbit (trans-GEO), the nature of the acceleration mechanism and the importance of DFBs in generating injections inside geosynchronous orbit (cis-GEO) are unclear. Our statistical study of cis-GEO DFBs using data from the Van Allen Probes reveals that just like trans-GEO DFBs, cis-GEO DFBs occur most often in the pre-midnight sector, but their occurrence rate is ~1/3 that of trans-GEO DFBs. Half the cis-GEO DFBs are accompanied by an energetic particle injection and have an electric field three times stronger than that of the injectionless half. All DFB injections are dispersionless within the temporal resolution considered (11 seconds). Our findings suggest that these injections are ushered or produced locally by the DFB, and the DFB\textquoterights strong electric field is an important aspect of the injection generation mechanism. Liu, Jiang; Angelopoulos, V.; Zhang, Xiao-Jia; Turner, D.; Gabrielse, C.; Runov, A.; Li, Jinxing; Funsten, H.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2016 YEAR: 2016 DOI: 10.1002/2015JA021691 dipolarization front; dipolarizing flux bundle; energetic particle injection; geosynchronous orbit; magnetic storm; Particle acceleration |
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Nonlinearity in chorus waves during a geomagnetic storm on 1 November 2012 In this study, we investigate the possibility of nonlinearity in chorus waves during a geomagnetic storm on 1 November 2012. The data we use were measured by the Van Allen Probe B. Wave data and plasma sheet electron data are analyzed. Chorus waves were frequently measured in the morning side during the main phase of this storm. Large-amplitude chorus waves were seen of the order of \~0.6 nT and >7 mV/m, which are similar to or larger than the typical ULF waves. The waves quite often consist of rising tones during the burst sampling. Since the rising tone is known as a signature of nonlinearity, a large portion of the waves are regarded as nonlinear at least during the burst sampling periods. These results underline the importance of nonlinearity in the dynamics of chorus waves. We further compare the measurement and the nonlinear theories, based on the inhomogeneity ratio, our own calculation derived from the field equation and the backward wave oscillator model. The wave quantities examined are frequency, amplitude, frequency drift rate, and duration. This type of study is useful to more deeply understand wave-particle interactions and hence may lead to predicting the generation and loss of radiation belt electrons in the future. Matsui, H.; Paulson, K.; Torbert, R.; Spence, H.; Kletzing, C.; Kurth, W.; Skoug, R.; Larsen, B.; Breneman, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2016 YEAR: 2016 DOI: 10.1002/2015JA021772 chorus waves; Geomagnetic storm; nonlinearity; Van Allen Probes |
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We examined an electron flux dropout during the 12\textendash14 November 2012 geomagnetic storm using observations from seven spacecraft: the two Van Allen Probes, THEMIS-A (P5), Cluster 2, and Geostationary Operational Environmental Satellite (GOES) 13, 14, and 15. The electron fluxes for energies greater than 2.0 MeV observed by GOES 13, 14, and 15 at geosynchronous orbit and by the Van Allen Probes remained at or near instrumental background levels for more than 24 hours from 12\textendash14 November. For energies of 0.8 MeV, the GOES satellites observed two shorter intervals of reduced electron fluxes. The first interval of reduced 0.8 MeV electron fluxes on 12\textendash13 November was associated with an interplanetary shock and a sudden impulse. Cluster, THEMIS, and GOES observed intense He+ EMIC waves from just inside geosynchronous orbit out to the magnetopause across the dayside to the dusk flank. The second interval of reduced 0.8 MeV electron fluxes on 13\textendash14 November was associated with a solar sector boundary crossing and development of a geomagnetic storm with Dst < -100 nT. At the start of the recovery phase, both the 0.8 and 2.0 MeV electron fluxes finally returned to near pre-storm values, possibly in response to strong ultra-low frequency (ULF) waves observed by the Van Allen Probes near dawn. A combination of adiabatic effects, losses to the magnetopause, scattering by EMIC waves, and acceleration by ULF waves can explain the observed electron behavior. Sigsbee, K.; Kletzing, C.; Smith, C.; MacDowall, Robert; Spence, Harlan; Reeves, Geoff; Blake, J.; Baker, D.; Green, J.; Singer, H.; Carr, C.; ik, O.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2016 YEAR: 2016 DOI: 10.1002/2014JA020877 Dst Effect; Electron Flux Dropouts; EMIC waves; magnetopause shadowing; ULF Pulsations; Van Allen Probes |
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We examined an electron flux dropout during the 12\textendash14 November 2012 geomagnetic storm using observations from seven spacecraft: the two Van Allen Probes, THEMIS-A (P5), Cluster 2, and Geostationary Operational Environmental Satellite (GOES) 13, 14, and 15. The electron fluxes for energies greater than 2.0 MeV observed by GOES 13, 14, and 15 at geosynchronous orbit and by the Van Allen Probes remained at or near instrumental background levels for more than 24 hours from 12\textendash14 November. For energies of 0.8 MeV, the GOES satellites observed two shorter intervals of reduced electron fluxes. The first interval of reduced 0.8 MeV electron fluxes on 12\textendash13 November was associated with an interplanetary shock and a sudden impulse. Cluster, THEMIS, and GOES observed intense He+ EMIC waves from just inside geosynchronous orbit out to the magnetopause across the dayside to the dusk flank. The second interval of reduced 0.8 MeV electron fluxes on 13\textendash14 November was associated with a solar sector boundary crossing and development of a geomagnetic storm with Dst < -100 nT. At the start of the recovery phase, both the 0.8 and 2.0 MeV electron fluxes finally returned to near pre-storm values, possibly in response to strong ultra-low frequency (ULF) waves observed by the Van Allen Probes near dawn. A combination of adiabatic effects, losses to the magnetopause, scattering by EMIC waves, and acceleration by ULF waves can explain the observed electron behavior. Sigsbee, K.; Kletzing, C.; Smith, C.; MacDowall, Robert; Spence, Harlan; Reeves, Geoff; Blake, J.; Baker, D.; Green, J.; Singer, H.; Carr, C.; ik, O.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2016 YEAR: 2016 DOI: 10.1002/2014JA020877 Dst Effect; Electron Flux Dropouts; EMIC waves; magnetopause shadowing; ULF Pulsations; Van Allen Probes |
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We examined an electron flux dropout during the 12\textendash14 November 2012 geomagnetic storm using observations from seven spacecraft: the two Van Allen Probes, THEMIS-A (P5), Cluster 2, and Geostationary Operational Environmental Satellite (GOES) 13, 14, and 15. The electron fluxes for energies greater than 2.0 MeV observed by GOES 13, 14, and 15 at geosynchronous orbit and by the Van Allen Probes remained at or near instrumental background levels for more than 24 hours from 12\textendash14 November. For energies of 0.8 MeV, the GOES satellites observed two shorter intervals of reduced electron fluxes. The first interval of reduced 0.8 MeV electron fluxes on 12\textendash13 November was associated with an interplanetary shock and a sudden impulse. Cluster, THEMIS, and GOES observed intense He+ EMIC waves from just inside geosynchronous orbit out to the magnetopause across the dayside to the dusk flank. The second interval of reduced 0.8 MeV electron fluxes on 13\textendash14 November was associated with a solar sector boundary crossing and development of a geomagnetic storm with Dst < -100 nT. At the start of the recovery phase, both the 0.8 and 2.0 MeV electron fluxes finally returned to near pre-storm values, possibly in response to strong ultra-low frequency (ULF) waves observed by the Van Allen Probes near dawn. A combination of adiabatic effects, losses to the magnetopause, scattering by EMIC waves, and acceleration by ULF waves can explain the observed electron behavior. Sigsbee, K.; Kletzing, C.; Smith, C.; MacDowall, Robert; Spence, Harlan; Reeves, Geoff; Blake, J.; Baker, D.; Green, J.; Singer, H.; Carr, C.; ik, O.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2016 YEAR: 2016 DOI: 10.1002/2014JA020877 Dst Effect; Electron Flux Dropouts; EMIC waves; magnetopause shadowing; ULF Pulsations; Van Allen Probes |
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We report measurements of energized outflowing/bouncing ionospheric ions and heated electrons in the inner magnetosphere during a geomagnetic storm. The ions arrive in the equatorial plane with pitch angles that increase with energy over a range from tens of eV to > 50 keV while the electrons are field-aligned up to ~1 keV. These particle distributions are observed during intervals of broadband low frequency electromagnetic field fluctuations consistent with a Doppler-shifted spectrum of kinetic Alfv\ en waves and kinetic field-line resonances. The fluctuations extend from L≈3 out to the apogee of the Van Allen Probes spacecraft at L≈6.5. They thereby span most of the L-shell range occupied by the ring current. These measurements suggest a model for ionospheric ion outflow and energization driven by dispersive Alfv\ en waves that may account for the large storm-time contribution of ionospheric ions to magnetospheric energy density. Chaston, C.; Bonnell, J.; Wygant, J.; Kletzing, C.; Reeves, G.; Gerrard, A.; Lanzerotti, L.; Smith, C.; Published by: Geophysical Research Letters Published on: 12/2015 YEAR: 2015 DOI: 10.1002/2015GL066674 Alfven waves; electron precipitation; Geomagnetic storms; ion acceleration; ion outflow; ion upflo |
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Nonlinear Generation of Electromagnetic Waves through Induced Scattering by Thermal Plasma We demonstrate the conversion of electrostatic pump waves into electromagnetic waves through nonlinear induced scattering by thermal particles in a laboratory plasma. Electrostatic waves in the whistler branch are launched that propagate near the resonance cone. When the amplitude exceeds a threshold ~5 \texttimes 10-6 times the background magnetic field, wave power is scattered below the pump frequency with wave normal angles (~59\textdegree), where the scattered wavelength reaches the limits of the plasma column. The scattered wave has a perpendicular wavelength that is an order of magnitude larger than the pump wave and longer than the electron skin depth. The amplitude threshold, scattered frequency spectrum, and scattered wave normal angles are in good agreement with theory. The results may affect the analysis and interpretation of space observations and lead to a comprehensive understanding of the nature of the Earth\textquoterights plasma environment. Tejero, E.; Crabtree, C.; Blackwell, D.; Amatucci, W.; Mithaiwala, M.; Ganguli, G.; Rudakov, L.; Published by: Scientific Reports Published on: 12/2015 YEAR: 2015 DOI: 10.1038/srep17852 |
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Nonlinear Generation of Electromagnetic Waves through Induced Scattering by Thermal Plasma We demonstrate the conversion of electrostatic pump waves into electromagnetic waves through nonlinear induced scattering by thermal particles in a laboratory plasma. Electrostatic waves in the whistler branch are launched that propagate near the resonance cone. When the amplitude exceeds a threshold ~5 \texttimes 10-6 times the background magnetic field, wave power is scattered below the pump frequency with wave normal angles (~59\textdegree), where the scattered wavelength reaches the limits of the plasma column. The scattered wave has a perpendicular wavelength that is an order of magnitude larger than the pump wave and longer than the electron skin depth. The amplitude threshold, scattered frequency spectrum, and scattered wave normal angles are in good agreement with theory. The results may affect the analysis and interpretation of space observations and lead to a comprehensive understanding of the nature of the Earth\textquoterights plasma environment. Tejero, E.; Crabtree, C.; Blackwell, D.; Amatucci, W.; Mithaiwala, M.; Ganguli, G.; Rudakov, L.; Published by: Scientific Reports Published on: 12/2015 YEAR: 2015 DOI: 10.1038/srep17852 |
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Nonlinear Generation of Electromagnetic Waves through Induced Scattering by Thermal Plasma We demonstrate the conversion of electrostatic pump waves into electromagnetic waves through nonlinear induced scattering by thermal particles in a laboratory plasma. Electrostatic waves in the whistler branch are launched that propagate near the resonance cone. When the amplitude exceeds a threshold ~5 \texttimes 10-6 times the background magnetic field, wave power is scattered below the pump frequency with wave normal angles (~59\textdegree), where the scattered wavelength reaches the limits of the plasma column. The scattered wave has a perpendicular wavelength that is an order of magnitude larger than the pump wave and longer than the electron skin depth. The amplitude threshold, scattered frequency spectrum, and scattered wave normal angles are in good agreement with theory. The results may affect the analysis and interpretation of space observations and lead to a comprehensive understanding of the nature of the Earth\textquoterights plasma environment. Tejero, E.; Crabtree, C.; Blackwell, D.; Amatucci, W.; Mithaiwala, M.; Ganguli, G.; Rudakov, L.; Published by: Scientific Reports Published on: 12/2015 YEAR: 2015 DOI: 10.1038/srep17852 |
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Observations of discrete magnetosonic waves off the magnetic equator Fast mode magnetosonic waves are typically confined close to the magnetic equator and exhibit harmonic structures at multiples of the local, equatorial proton cyclotron frequency. We report observations of magnetosonic waves well off the equator at geomagnetic latitudes from -16.5\textdegreeto -17.9\textdegree and L shell ~2.7\textendash4.6. The observed waves exhibit discrete spectral structures with multiple frequency spacings. The predominant frequency spacings are ~6 and 9 Hz, neither of which is equal to the local proton cyclotron frequency. Backward ray tracing simulations show that the feature of multiple frequency spacings is caused by propagation from two spatially narrow equatorial source regions located at L ≈ 4.2 and 3.7. The equatorial proton cyclotron frequencies at those two locations match the two observed frequency spacings. Our analysis provides the first observations of the harmonic nature of magnetosonic waves well away from the equatorial region and suggests that the propagation from multiple equatorial sources contributes to these off-equatorial magnetosonic emissions with varying frequency spacings. Zhima, Zeren; Chen, Lunjin; Fu, Huishan; Cao, Jinbin; Horne, Richard; Reeves, Geoff; Published by: Geophysical Research Letters Published on: 12/2015 YEAR: 2015 DOI: 10.1002/2015GL066255 |
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Observations of discrete magnetosonic waves off the magnetic equator Fast mode magnetosonic waves are typically confined close to the magnetic equator and exhibit harmonic structures at multiples of the local, equatorial proton cyclotron frequency. We report observations of magnetosonic waves well off the equator at geomagnetic latitudes from -16.5\textdegreeto -17.9\textdegree and L shell ~2.7\textendash4.6. The observed waves exhibit discrete spectral structures with multiple frequency spacings. The predominant frequency spacings are ~6 and 9 Hz, neither of which is equal to the local proton cyclotron frequency. Backward ray tracing simulations show that the feature of multiple frequency spacings is caused by propagation from two spatially narrow equatorial source regions located at L ≈ 4.2 and 3.7. The equatorial proton cyclotron frequencies at those two locations match the two observed frequency spacings. Our analysis provides the first observations of the harmonic nature of magnetosonic waves well away from the equatorial region and suggests that the propagation from multiple equatorial sources contributes to these off-equatorial magnetosonic emissions with varying frequency spacings. Zhima, Zeren; Chen, Lunjin; Fu, Huishan; Cao, Jinbin; Horne, Richard; Reeves, Geoff; Published by: Geophysical Research Letters Published on: 12/2015 YEAR: 2015 DOI: 10.1002/2015GL066255 |
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A statistical survey of electron pitch angle distributions (PADs) is performed based on the pitch angle resolved flux observations from the Magnetic Electron Ion Spectrometer (MagEIS) instrument on board the Van Allen Probes during the period from 1 October 2012 to 1 May 2015. By fitting the measured PADs to a sinnα form, where α is the local pitch angle and n is the power law index, we investigate the dependence of PADs on electron kinetic energy, magnetic local time (MLT), the geomagnetic Kp index and L-shell. The difference in electron PADs between the inner and outer belt is distinct. In the outer belt, the common averaged n values are less than 1.5, except for large values of the Kp index and high electron energies. The averaged n values vary considerably with MLT, with a peak in the afternoon sector and an increase with increasing L-shell. In the inner belt, the averaged n values are much larger, with a common value greater than 2. The PADs show a slight dependence on MLT, with a weak maximum at noon. A distinct region with steep PADs lies in the outer edge of the inner belt where the electron flux is relatively low. The distance between the inner and outer belt and the intensity of the geomagnetic activity together determine the variation of PADs in the inner belt. Besides being dependent on electron energy, magnetic activity and L-shell, the results show a clear dependence on MLT, with higher n values on the dayside. Shi, Run; Summers, Danny; Ni, Binbin; Fennell, Joseph; Blake, Bernard; Spence, Harlan; Reeves, Geoffrey; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2015 YEAR: 2015 DOI: 10.1002/2015JA021724 |
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Ultra-low-frequency wave-driven diffusion of radiation belt relativistic electrons Van Allen radiation belts are typically two zones of energetic particles encircling the Earth separated by the slot region. How the outer radiation belt electrons are accelerated to relativistic energies remains an unanswered question. Recent studies have presented compelling evidence for the local acceleration by very-low-frequency (VLF) chorus waves. However, there has been a competing theory to the local acceleration, radial diffusion by ultra-low-frequency (ULF) waves, whose importance has not yet been determined definitively. Here we report a unique radiation belt event with intense ULF waves but no detectable VLF chorus waves. Our results demonstrate that the ULF waves moved the inner edge of the outer radiation belt earthward 0.3 Earth radii and enhanced the relativistic electron fluxes by up to one order of magnitude near the slot region within about 10 h, providing strong evidence for the radial diffusion of radiation belt relativistic electrons. Su, Zhenpeng; Zhu, Hui; Xiao, Fuliang; Zong, Q.-G.; Zhou, X.-Z.; Zheng, Huinan; Wang, Yuming; Wang, Shui; Hao, Y.-X.; Gao, Zhonglei; He, Zhaoguo; Baker, D.; Spence, H.; Reeves, G.; Blake, J.; Wygant, J.; Published by: Nature Communications Published on: 12/2015 YEAR: 2015 DOI: 10.1038/ncomms10096 |
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Energy dependent dynamics of keV to MeV electrons in the inner zone, outer zone, and slot regions. We present observations of the radiation belts from the HOPE and MagEIS particle detectors on the Van Allen Probes satellites that illustrate the energy-dependence and L-shell dependence of radiation belt enhancements and decays. We survey events in 2013 and analyze an event on March 1 in more detail. The observations show: (a) At all L-shells, lower-energy electrons are enhanced more often than higher energies; (b) Events that fill the slot region are more common at lower energies; (c) Enhancements of electrons in the inner zone are more common at lower energies; and (d) Even when events do not fully fill the slot region, enhancements at lower-energies tend to extend to lower L-shells than higher energies. During enhancement events the outer zone extends to lower L-shells at lower energies while being confined to higher L-shells at higher energies. The inner zone shows the opposite with an outer boundary at higher L-shells for lower energies. Both boundaries are nearly straight in log(energy) vs. L-shell space. At energies below a few hundred keV radiation belt electron penetration through the slot region into the inner zone is commonplace but the number and frequency of \textquotedblleftslot filling\textquotedblright events decreases with increasing energy. The inner zone is enhanced only at energies that penetrate through the slot. Energy- and L-shell dependent losses (that are consistent with whistler hiss interactions) return the belts to more quiescent conditions. Reeves, Geoffrey; Friedel, Reiner; Larsen, Brian; Skoug, Ruth; Funsten, Herbert; Claudepierre, Seth; Fennell, Joseph; Turner, Drew; Denton, Mick; Spence, H.; Blake, Bernard; Baker, D.; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2015 YEAR: 2015 DOI: 10.1002/2015JA021569 Acceleration; energetic particles; Inner zone; Outer Zone; Radiation belts; Slot region; Van Allen Probes |
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Energy dependent dynamics of keV to MeV electrons in the inner zone, outer zone, and slot regions. We present observations of the radiation belts from the HOPE and MagEIS particle detectors on the Van Allen Probes satellites that illustrate the energy-dependence and L-shell dependence of radiation belt enhancements and decays. We survey events in 2013 and analyze an event on March 1 in more detail. The observations show: (a) At all L-shells, lower-energy electrons are enhanced more often than higher energies; (b) Events that fill the slot region are more common at lower energies; (c) Enhancements of electrons in the inner zone are more common at lower energies; and (d) Even when events do not fully fill the slot region, enhancements at lower-energies tend to extend to lower L-shells than higher energies. During enhancement events the outer zone extends to lower L-shells at lower energies while being confined to higher L-shells at higher energies. The inner zone shows the opposite with an outer boundary at higher L-shells for lower energies. Both boundaries are nearly straight in log(energy) vs. L-shell space. At energies below a few hundred keV radiation belt electron penetration through the slot region into the inner zone is commonplace but the number and frequency of \textquotedblleftslot filling\textquotedblright events decreases with increasing energy. The inner zone is enhanced only at energies that penetrate through the slot. Energy- and L-shell dependent losses (that are consistent with whistler hiss interactions) return the belts to more quiescent conditions. Reeves, Geoffrey; Friedel, Reiner; Larsen, Brian; Skoug, Ruth; Funsten, Herbert; Claudepierre, Seth; Fennell, Joseph; Turner, Drew; Denton, Mick; Spence, H.; Blake, Bernard; Baker, D.; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2015 YEAR: 2015 DOI: 10.1002/2015JA021569 Acceleration; energetic particles; Inner zone; Outer Zone; Radiation belts; Slot region; Van Allen Probes |
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Evolution of lower hybrid turbulence in the ionosphere Three-dimensional evolution of the lower hybrid turbulence driven by a spatially localized ion ring beam perpendicular to the ambient magnetic field in space plasmas is analyzed. It is shown that the quasi-linear saturation model breaks down when the nonlinear rate of scattering by thermal electron is larger than linear damping rates, which can occur even for low wave amplitudes. The evolution is found to be essentially a three-dimensional phenomenon, which cannot be accurately explained by two-dimensional simulations. An important feature missed in previous studies of this phenom- enon is the nonlinear conversion of electrostatic lower hybrid waves into electromagnetic whistler and magnetosonic waves and the consequent energy loss due to radiation from the source region. This can result in unique low-amplitude saturation with extended saturation time. It is shown that when the nonlinear effects are considered the net energy that can be permanently extracted from the ring beam is larger. The results are applied to anticipate the outcome of a planned experiment that will seed lower hybrid turbulence in the ionosphere and monitor its evolution. Ganguli, G.; Crabtree, C.; Mithaiwala, M.; Rudakov, L.; Scales, W.; Published by: Physics of Plasmas Published on: 11/2015 YEAR: 2015 DOI: 10.1063/1.4936281 |
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Evolution of lower hybrid turbulence in the ionosphere Three-dimensional evolution of the lower hybrid turbulence driven by a spatially localized ion ring beam perpendicular to the ambient magnetic field in space plasmas is analyzed. It is shown that the quasi-linear saturation model breaks down when the nonlinear rate of scattering by thermal electron is larger than linear damping rates, which can occur even for low wave amplitudes. The evolution is found to be essentially a three-dimensional phenomenon, which cannot be accurately explained by two-dimensional simulations. An important feature missed in previous studies of this phenom- enon is the nonlinear conversion of electrostatic lower hybrid waves into electromagnetic whistler and magnetosonic waves and the consequent energy loss due to radiation from the source region. This can result in unique low-amplitude saturation with extended saturation time. It is shown that when the nonlinear effects are considered the net energy that can be permanently extracted from the ring beam is larger. The results are applied to anticipate the outcome of a planned experiment that will seed lower hybrid turbulence in the ionosphere and monitor its evolution. Ganguli, G.; Crabtree, C.; Mithaiwala, M.; Rudakov, L.; Scales, W.; Published by: Physics of Plasmas Published on: 11/2015 YEAR: 2015 DOI: 10.1063/1.4936281 |
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Global Empirical Models of Plasmaspheric Hiss using Van Allen Probes Plasmaspheric hiss is a whistler mode emission that permeates the Earth\textquoterights plasmasphere and is a significant driver of energetic electron losses through cyclotron-resonant pitch angle scattering. The EMFISIS instrument on the Van Allen Probes mission provides vastly improved measurements of the hiss wave environment including continuous measurements of the wave magnetic field cross-spectral matrix and enhanced low frequency coverage. Here, we develop empirical models of hiss wave intensity using two years of Van Allen Probes data. First, we describe the construction of the hiss database. Then, we compare the hiss spectral distribution and integrated wave amplitude obtained from Van Allen Probes to those previously extracted from the CRRES mission. Next, we develop a cubic regression model of the average hiss magnetic field intensity as a function of Kp, L, magnetic latitude and magnetic local time. We use the full regression model to explore general trends in the data and use insights from the model to develop a simplified model of wave intensity for straightforward inclusion in quasi-linear diffusion calculations of electron scattering rates. Spasojevic, M.; Shprits, Y.Y.; Orlova, K.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2015 YEAR: 2015 DOI: 10.1002/2015JA021803 Electron scattering; Empirical Model; inner magnetosphere; Plasmaspheric Hiss; Van Allen Probes |
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High-resolution in situ observations of electron precipitation-causing EMIC waves Electromagnetic ion cyclotron (EMIC) waves are thought to be important drivers of energetic electron losses from the outer radiation belt through precipitation into the atmosphere. While the theoretical possibility of pitch angle scattering-driven losses from these waves has been recognized for more than four decades, there have been limited experimental precipitation observations to support this concept. We have combined satellite-based observations of the characteristics of EMIC waves, with satellite and ground-based observations of the EMIC-induced electron precipitation. In a detailed case study, supplemented by an additional four examples, we are able to constrain for the first time the location, size, and energy range of EMIC-induced electron precipitation inferred from coincident precipitation data and relate them to the EMIC wave frequency, wave power, and ion band of the wave as measured in situ by the Van Allen Probes. These observations will better constrain modeling into the importance of EMIC wave-particle interactions. Rodger, Craig; Hendry, Aaron; Clilverd, Mark; Kletzing, Craig; Brundell, James; Reeves, Geoffrey; Published by: Geophysical Research Letters Published on: 11/2015 YEAR: 2015 DOI: 10.1002/grl.v42.2210.1002/2015GL066581 EMIC waves; energetic electron precipitation; radiation belt electrons; Van Allen Probes; wave-particle interactions |
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On 2 October 2013, the arrival of an interplanetary shock compressed the Earth\textquoterights magnetosphere and triggered a global ULF (ultra low frequency) oscillation. The Van Allen Probe B spacecraft observed this large-amplitude ULF wave in situ with both magnetic and electric field data. Broadband waves up to approximately 100 Hz were observed in conjunction with, and modulated by, this ULF wave. Detailed analysis of fields and particle data reveals that these broadband waves are Doppler-shifted kinetic Alfv\ en waves. This event suggests that magnetospheric compression by interplanetary shocks can induce abrupt generation of kinetic Alfv\ en waves over large portions of the inner magnetosphere, potentially driving previously unconsidered wave-particle interactions throughout the inner magnetosphere during the initial response of the magnetosphere to shock impacts. Malaspina, David; Claudepierre, Seth; Takahashi, Kazue; Jaynes, Allison; Elkington, Scot; Ergun, Robert; Wygant, John; Reeves, Geoff; Kletzing, Craig; Published by: Geophysical Research Letters Published on: 11/2015 YEAR: 2015 DOI: 10.1002/2015GL065935 inner magnetosphere; interplanetary shock; Kinetic Alfven Waves; magnetosphere shock response; plasma waves; ULF waves; Van Allen Probes |
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By examining the compression-induced changes in the electron phase space density and pitch angle distribution observed by two satellites of Van Allen Probes (RBSP-A/B), we find that the relativistic electrons (>2MeV) outside the heart of outer radiation belt (L*>= 5) undergo multiple losses during a storm sudden commencement (SSC). The relativistic electron loss mainly occurs in the field-aligned direction (pitch angle α< 30\textdegree or >150\textdegree), and the flux decay of the field-aligned electrons is independent of the spatial location variations of the two satellites. However, the relativistic electrons in the pitch angle range of 30\textdegree-150\textdegree increase (decrease) with the decreasing (increasing) geocentric distance (|ΔL|< 0.25) of the RBSP-B (RBSP-A) location, and the electron fluxes in the quasi-perpendicular direction display energy-dispersive oscillations in the Pc5 period range (2 - 10min). The relativistic electron loss is confirmed by the decrease of electron phase space density at high-L shell after the magnetospheric compressions, and their loss is associated with the intense plasmaspheric hiss, electromagnetic ion cyclotron (EMIC) waves, relativistic electron precipitation (observed by POES/NOAA satellites at 850km) and magnetic field fluctuations in the Pc5 band. The intense EMIC waves and whistler-mode hiss jointly cause the rapidly pitch angle scattering loss of the relativistic electrons within 10 hours. Moreover, the Pc5 ULF waves also lead to the slowly outward radial diffusion of the relativistic electrons in the high-L region with a negative electron phase space density gradient. Yu, J.; Li, L.Y.; Cao, J.; Yuan, Z.; Reeves, G.; Baker, D.; Blake, J.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2015 YEAR: 2015 DOI: 10.1002/2015JA021460 Electromagnetic ion cyclotron (EMIC) waves; outer radiation belt; Outward radial diffusion driven by ULF waves; Plasmaspheric Hiss; relativistic electron loss; Storm sudden commencement; Van Allen Probes |
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By examining the compression-induced changes in the electron phase space density and pitch angle distribution observed by two satellites of Van Allen Probes (RBSP-A/B), we find that the relativistic electrons (>2MeV) outside the heart of outer radiation belt (L*>= 5) undergo multiple losses during a storm sudden commencement (SSC). The relativistic electron loss mainly occurs in the field-aligned direction (pitch angle α< 30\textdegree or >150\textdegree), and the flux decay of the field-aligned electrons is independent of the spatial location variations of the two satellites. However, the relativistic electrons in the pitch angle range of 30\textdegree-150\textdegree increase (decrease) with the decreasing (increasing) geocentric distance (|ΔL|< 0.25) of the RBSP-B (RBSP-A) location, and the electron fluxes in the quasi-perpendicular direction display energy-dispersive oscillations in the Pc5 period range (2 - 10min). The relativistic electron loss is confirmed by the decrease of electron phase space density at high-L shell after the magnetospheric compressions, and their loss is associated with the intense plasmaspheric hiss, electromagnetic ion cyclotron (EMIC) waves, relativistic electron precipitation (observed by POES/NOAA satellites at 850km) and magnetic field fluctuations in the Pc5 band. The intense EMIC waves and whistler-mode hiss jointly cause the rapidly pitch angle scattering loss of the relativistic electrons within 10 hours. Moreover, the Pc5 ULF waves also lead to the slowly outward radial diffusion of the relativistic electrons in the high-L region with a negative electron phase space density gradient. Yu, J.; Li, L.Y.; Cao, J.; Yuan, Z.; Reeves, G.; Baker, D.; Blake, J.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2015 YEAR: 2015 DOI: 10.1002/2015JA021460 Electromagnetic ion cyclotron (EMIC) waves; outer radiation belt; Outward radial diffusion driven by ULF waves; Plasmaspheric Hiss; relativistic electron loss; Storm sudden commencement; Van Allen Probes |
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The Van Allen radiation belts surrounding the Earth are filled with MeV-energy electrons. This region poses ionizing radiation risks for spacecraft that operate within it, including those in geostationary (GEO) and medium Earth orbit (MEO). To provide alerts of electron flux enhancements, sixteen prediction models of the electron log-flux variation throughout the equatorial outer radiation belt as a function of the McIlwain L parameter were developed using the multivariate autoregressive model and Kalman filter. Measurements of omni-directional 2.3 MeV electron flux from the Van Allen Probes mission as well as >2 MeV electrons from the GOES-15 spacecraft were used as the predictors. Model explanatory parameters were selected from solar wind parameters, the electron log-flux at GEO, and geomagnetic indices. For the innermost region of the outer radiation belt, the electron flux is best predicted by using the Dst index as the sole input parameter. For the central to outermost regions, at L≧4.8 and L≧5.6, the electron flux is predicted most accurately by including also the solar wind velocity and then the dynamic pressure, respectively. The Dst index is the best overall single parameter for predicting at 3≦L≦6, while for the GEO flux prediction, the KP index is better than Dst. A test calculation demonstrates that the model successfully predicts the timing and location of the flux maximum as much as 2 days in advance, and that the electron flux decreases faster with time at higher L values, both model features consistent with the actually observed behavior. Sakaguchi, Kaori; Nagatsuma, Tsutomu; Reeves, Geoffrey; Spence, Harlan; Published by: Space Weather Published on: 11/2015 YEAR: 2015 DOI: 10.1002/2015SW001254 outer radiation belt; Practical prediction model; Van Allen Probes |
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The Van Allen radiation belts surrounding the Earth are filled with MeV-energy electrons. This region poses ionizing radiation risks for spacecraft that operate within it, including those in geostationary (GEO) and medium Earth orbit (MEO). To provide alerts of electron flux enhancements, sixteen prediction models of the electron log-flux variation throughout the equatorial outer radiation belt as a function of the McIlwain L parameter were developed using the multivariate autoregressive model and Kalman filter. Measurements of omni-directional 2.3 MeV electron flux from the Van Allen Probes mission as well as >2 MeV electrons from the GOES-15 spacecraft were used as the predictors. Model explanatory parameters were selected from solar wind parameters, the electron log-flux at GEO, and geomagnetic indices. For the innermost region of the outer radiation belt, the electron flux is best predicted by using the Dst index as the sole input parameter. For the central to outermost regions, at L≧4.8 and L≧5.6, the electron flux is predicted most accurately by including also the solar wind velocity and then the dynamic pressure, respectively. The Dst index is the best overall single parameter for predicting at 3≦L≦6, while for the GEO flux prediction, the KP index is better than Dst. A test calculation demonstrates that the model successfully predicts the timing and location of the flux maximum as much as 2 days in advance, and that the electron flux decreases faster with time at higher L values, both model features consistent with the actually observed behavior. Sakaguchi, Kaori; Nagatsuma, Tsutomu; Reeves, Geoffrey; Spence, Harlan; Published by: Space Weather Published on: 11/2015 YEAR: 2015 DOI: 10.1002/2015SW001254 outer radiation belt; Practical prediction model; Van Allen Probes |
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Responses of relativistic electron fluxes in the outer radiation belt to geomagnetic storms Geomagnetic storms can either increase or decrease relativistic electron fluxes in the outer radiation belt. A statistical survey of 84 isolated storms demonstrates that geomagnetic storms preferentially decrease relativistic electron fluxes at higher energies, while flux enhancements are more common at lower energies. In about 87\% of the storms, 0.3\textendash2.5 MeV electron fluxes show an increase, whereas 2.5\textendash14 MeV electron fluxes increase in only 35\% of the storms. Superposed epoch analyses suggest that such \textquotedblleftenergy-dependent\textquotedblright responses of electrons preferably occur during conditions of high solar wind density which is favorable to generate magnetospheric electromagnetic ion cyclotron (EMIC) waves, and these events are associated with relatively weaker chorus activities. We have examined one of the cases where observed EMIC waves can resonate effectively with >2.5 MeV electrons and scatter them into the atmosphere. The correlation study further illustrates that electron flux dropouts during storm main phases do not correlate well with the flux buildup during storm recovery phases. We suggest that a combination of efficient EMIC-induced scattering and weaker chorus-driven acceleration provides a viable candidate for the energy-dependent responses of outer radiation belt relativistic electrons to geomagnetic storms. These results are of great interest to both understanding of the radiation belt dynamics and applications in space weather. Xiong, Ying; Xie, Lun; Pu, Zuyin; Fu, Suiyan; Chen, Lunjin; Ni, Binbin; Li, Wen; Li, Jinxing; Guo, Ruilong; Parks, G.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2015 YEAR: 2015 DOI: 10.1002/2015JA021440 energy dependence; Geomagnetic storm; Radiation belts; relativistic electrons; Solar wind |
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Electron distribution function formation in regions of diffuse aurora The precipitation of high-energy magnetospheric electrons (E \~ 600 eV\textendash10 KeV) in the diffuse aurora contributes significant energy flux into the Earth\textquoterights ionosphere. To fully understand the formation of this flux at the upper ionospheric boundary, \~700\textendash800 km, it is important to consider the coupled ionosphere-magnetosphere system. In the diffuse aurora, precipitating electrons initially injected from the plasma sheet via wave-particle interaction processes degrade in the atmosphere toward lower energies and produce secondary electrons via impact ionization of the neutral atmosphere. These precipitating electrons can be additionally reflected upward from the two conjugate ionospheres, leading to a series of multiple reflections through the magnetosphere. These reflections greatly influence the initially precipitating flux at the upper ionospheric boundary (700\textendash800 km) and the resultant population of secondary electrons and electrons cascading toward lower energies. In this paper, we present the solution of the Boltzman-Landau kinetic equation that uniformly describes the entire electron distribution function in the diffuse aurora, including the affiliated production of secondary electrons (E < 600 eV) and its energy interplay in the magnetosphere and two conjugated ionospheres. This solution takes into account, for the first time, the formation of the electron distribution function in the diffuse auroral region, beginning with the primary injection of plasma sheet electrons via both electrostatic electron cyclotron harmonic waves and whistler mode chorus waves to the loss cone, and including their subsequent multiple atmospheric reflections in the two magnetically conjugated ionospheres. It is demonstrated that magnetosphere-ionosphere coupling is key in forming the electron distribution function in the diffuse auroral region. Khazanov, G.; Tripathi, A.; Sibeck, D.; Himwich, E.; Glocer, A.; Singhal, R.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2015 YEAR: 2015 DOI: 10.1002/2015JA021728 diffuse aurora; electron distribution; Wave-particle interaction |
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Electron distribution function formation in regions of diffuse aurora The precipitation of high-energy magnetospheric electrons (E \~ 600 eV\textendash10 KeV) in the diffuse aurora contributes significant energy flux into the Earth\textquoterights ionosphere. To fully understand the formation of this flux at the upper ionospheric boundary, \~700\textendash800 km, it is important to consider the coupled ionosphere-magnetosphere system. In the diffuse aurora, precipitating electrons initially injected from the plasma sheet via wave-particle interaction processes degrade in the atmosphere toward lower energies and produce secondary electrons via impact ionization of the neutral atmosphere. These precipitating electrons can be additionally reflected upward from the two conjugate ionospheres, leading to a series of multiple reflections through the magnetosphere. These reflections greatly influence the initially precipitating flux at the upper ionospheric boundary (700\textendash800 km) and the resultant population of secondary electrons and electrons cascading toward lower energies. In this paper, we present the solution of the Boltzman-Landau kinetic equation that uniformly describes the entire electron distribution function in the diffuse aurora, including the affiliated production of secondary electrons (E < 600 eV) and its energy interplay in the magnetosphere and two conjugated ionospheres. This solution takes into account, for the first time, the formation of the electron distribution function in the diffuse auroral region, beginning with the primary injection of plasma sheet electrons via both electrostatic electron cyclotron harmonic waves and whistler mode chorus waves to the loss cone, and including their subsequent multiple atmospheric reflections in the two magnetically conjugated ionospheres. It is demonstrated that magnetosphere-ionosphere coupling is key in forming the electron distribution function in the diffuse auroral region. Khazanov, G.; Tripathi, A.; Sibeck, D.; Himwich, E.; Glocer, A.; Singhal, R.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2015 YEAR: 2015 DOI: 10.1002/2015JA021728 diffuse aurora; electron distribution; Wave-particle interaction |
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Electron distribution function formation in regions of diffuse aurora The precipitation of high-energy magnetospheric electrons (E \~ 600 eV\textendash10 KeV) in the diffuse aurora contributes significant energy flux into the Earth\textquoterights ionosphere. To fully understand the formation of this flux at the upper ionospheric boundary, \~700\textendash800 km, it is important to consider the coupled ionosphere-magnetosphere system. In the diffuse aurora, precipitating electrons initially injected from the plasma sheet via wave-particle interaction processes degrade in the atmosphere toward lower energies and produce secondary electrons via impact ionization of the neutral atmosphere. These precipitating electrons can be additionally reflected upward from the two conjugate ionospheres, leading to a series of multiple reflections through the magnetosphere. These reflections greatly influence the initially precipitating flux at the upper ionospheric boundary (700\textendash800 km) and the resultant population of secondary electrons and electrons cascading toward lower energies. In this paper, we present the solution of the Boltzman-Landau kinetic equation that uniformly describes the entire electron distribution function in the diffuse aurora, including the affiliated production of secondary electrons (E < 600 eV) and its energy interplay in the magnetosphere and two conjugated ionospheres. This solution takes into account, for the first time, the formation of the electron distribution function in the diffuse auroral region, beginning with the primary injection of plasma sheet electrons via both electrostatic electron cyclotron harmonic waves and whistler mode chorus waves to the loss cone, and including their subsequent multiple atmospheric reflections in the two magnetically conjugated ionospheres. It is demonstrated that magnetosphere-ionosphere coupling is key in forming the electron distribution function in the diffuse auroral region. Khazanov, G.; Tripathi, A.; Sibeck, D.; Himwich, E.; Glocer, A.; Singhal, R.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2015 YEAR: 2015 DOI: 10.1002/2015JA021728 diffuse aurora; electron distribution; Wave-particle interaction |
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Electromagnetic ion cyclotron (EMIC) waves are closely related to precipitating loss of relativistic electrons in the radiation belts, and thereby, a model of the radiation belts requires inclusion of the pitch angle diffusion caused by EMIC waves. We estimated the pitch angle diffusion rates and the corresponding precipitation time scales caused by H and He band EMIC waves using the Tsyganenko 04 (T04) magnetic field model at their probable regions in terms of geomagnetic conditions. The results correspond to enhanced pitch angle diffusion rates and reduced precipitation time scales compared to those based on the dipole model, up to several orders of magnitude for storm times. While both the plasma density and the magnetic field strength varied in these calculations, the reduction of the magnetic field strength predicted by the T04 model was found to be the main cause of the enhanced diffusion rates relative to those with the dipole model for the same Li values, where Li is defined from the ionospheric foot points of the field lines. We note that the bounce-averaged diffusion rates were roughly proportional to the inversion of the equatorial magnetic field strength and thus suggest that scaling the diffusion rates with the magnetic field strength provides a good approximation to account for the effect of the realistic field model in the EMIC wave-pitch angle diffusion modeling. Bin Kang, Suk-; Min, Kyoung-Wook; Fok, Mei-Ching; Hwang, Junga; Choi, Cheong-Rim; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2015 YEAR: 2015 DOI: 10.1002/2014JA020644 EMIC waves; pitch angle diffusion rate; precipitation time scale; quasi-linear theory; realistic field model; Relativistic electron |
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Magnetotail processes and structures related to substorm growth phase/onset auroral arcs remain poorly understood mostly due to the lack of adequate observations. In this study we make a comparison between ground-based optical measurements of the premidnight growth phase/onset arcs at subauroral latitudes and magnetically conjugate measurements made by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) at ~780 km in altitude and by the Van Allen Probe B (RBSP-B) spacecraft crossing L values of ~5.0\textendash5.6 in the premidnight inner tail region. The conjugate observations offer a unique opportunity to examine the detailed features of the arc location relative to large-scale Birkeland currents and of the magnetospheric counterpart. Our main findings include (1) at the early stage of the growth phase the quiet auroral arc emerged ~4.3\textdegree equatorward of the boundary between the downward Region 2 (R2) and upward Region 1 (R1) currents; (2) shortly before the auroral breakup (poleward auroral expansion) the latitudinal separation between the arc and the R1/R2 demarcation narrowed to ~1.0\textdegree; (3) RBSP-B observed a magnetic field signature of a local upward field-aligned current (FAC) connecting the arc with the near-Earth tail when the spacecraft footprint was very close to the arc; and (4) the upward FAC signature was located on the tailward side of a local plasma pressure increase confined near L ~5.2\textendash5.4. These findings strongly suggest that the premidnight arc is connected to highly localized pressure gradients embedded in the near-tail R2 source region via the local upward FAC. Motoba, T.; Ohtani, S.; Anderson, B.; Korth, H.; Mitchell, D.; Lanzerotti, L.; Shiokawa, K.; Connors, M.; Kletzing, C.; Reeves, G.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2015 YEAR: 2015 DOI: 10.1002/jgra.v120.1010.1002/2015JA021676 FACs; growth phase/onset arc; M-I coupling; Van Allen Probes |
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Magnetotail processes and structures related to substorm growth phase/onset auroral arcs remain poorly understood mostly due to the lack of adequate observations. In this study we make a comparison between ground-based optical measurements of the premidnight growth phase/onset arcs at subauroral latitudes and magnetically conjugate measurements made by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) at ~780 km in altitude and by the Van Allen Probe B (RBSP-B) spacecraft crossing L values of ~5.0\textendash5.6 in the premidnight inner tail region. The conjugate observations offer a unique opportunity to examine the detailed features of the arc location relative to large-scale Birkeland currents and of the magnetospheric counterpart. Our main findings include (1) at the early stage of the growth phase the quiet auroral arc emerged ~4.3\textdegree equatorward of the boundary between the downward Region 2 (R2) and upward Region 1 (R1) currents; (2) shortly before the auroral breakup (poleward auroral expansion) the latitudinal separation between the arc and the R1/R2 demarcation narrowed to ~1.0\textdegree; (3) RBSP-B observed a magnetic field signature of a local upward field-aligned current (FAC) connecting the arc with the near-Earth tail when the spacecraft footprint was very close to the arc; and (4) the upward FAC signature was located on the tailward side of a local plasma pressure increase confined near L ~5.2\textendash5.4. These findings strongly suggest that the premidnight arc is connected to highly localized pressure gradients embedded in the near-tail R2 source region via the local upward FAC. Motoba, T.; Ohtani, S.; Anderson, B.; Korth, H.; Mitchell, D.; Lanzerotti, L.; Shiokawa, K.; Connors, M.; Kletzing, C.; Reeves, G.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2015 YEAR: 2015 DOI: 10.1002/jgra.v120.1010.1002/2015JA021676 FACs; growth phase/onset arc; M-I coupling; Van Allen Probes |
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Heavy-ion dominance near Cluster perigees Time periods in which heavy ions dominate over H+ in the energy range of 1-40 keV were observed by the Cluster Ion Spectrometry (CIS)/COmposition DIstribution Function (CODIF) instrument onboard Cluster Spacecraft 4 at L-values less than 4. The characteristic feature is a narrow flux peak at around 10 keV that extends into low L-values, with He+ and/or O+ dominating. In the present work we perform a statistical study of these events and examine their temporal occurrence and spatial distribution. The observed features, both the narrow energy range and the heavy-ion dominance, can be interpreted using a model of ion drift from the plasma sheet, subject to charge exchange losses. The narrow energy range corresponds to the only energy range that has direct drift access from the plasma sheet during quiet times. The drift time to these locations from the plasma sheet is > 30 hours, so that charge exchange has a significant impact on the population. We show that a simple drift/loss model can explain the dependence on L-shell and MLT of these heavy-ion-dominant time periods. Ferradas, C.; Zhang, J.-C.; Kistler, L.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2015 YEAR: 2015 DOI: 10.1002/2015JA021063 charge exchange; Cluster; heavy ions; inner magnetosphere; plasma sheet; ring current |
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Measurement of inner radiation belt electrons with kinetic energy above 1~MeV Data from the Proton-Electron Telescope on the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) satellite, taken during 1992\textendash2009, are analyzed for evidence of inner radiation belt electrons with kinetic energy E > 1 MeV. It is found that most of the data from a detector combination with a nominal energy threshold of 1 MeV were, in fact, caused by a chance coincidence response to lower energy electrons or high-energy protons. In particular, there was no detection of inner belt or slot region electrons above 1 MeV following the 2003 Halloween storm injection, though they may have been present. However, by restricting data to a less-stable, low-altitude trapping region, a persistent presence of inner belt electrons in the energy range 1 to 1.6 MeV is demonstrated. Their soft, exponential energy spectra are consistent with extrapolation of lower energy measurements. Published by: Journal of Geophysical Research: Space Physics Published on: 10/2015 YEAR: 2015 DOI: 10.1002/2015JA021387 |