Bibliography
|
Notice:
|
Found 113 entries in the Bibliography.
Showing entries from 101 through 113
| 2014 |
|
We have recently conducted a statistical survey on pitch angle distributions of energetic electrons trapped in the Earth\textquoterights outer radiation belt, and a new empirical model was developed based upon survey results. This model\textemdashrelativistic electron pitch angle distribution (REPAD)\textemdashaims to present statistical pictures of electron equatorial pitch angle distributions, instead of the absolute flux levels, as a function of energy, L shell, magnetic local time, and magnetic activity. To quantify and facilitate this statistical survey, we use Legendre polynomials to fit long-term in situ directional fluxes observed near the magnetic equator from three missions: CRRES, Polar, and LANL-97A. As the first of this kind of model, REPAD covers the whole outer belt region, providing not only the mean and median pitch angle distributions in the area but also error estimates of the average distributions. Preliminary verification and validation results demonstrate the reliable performance of this model. Usage of REPAD is mainly to predict the full pitch angle distribution of fluxes along a given magnetic field line, or even on a given drift shell, based upon one single unidirectional or omnidirectional flux measurement anywhere on that field line. This can be particularly useful for data assimilation, which usually has large tolerance on data errors. In addition, relatively small variations in pitch angle distributions measured at L shell between ~ 4 and 5 justify the assumption of fixed pitch angle distributions at GPS equatorial crossings (L ~ 4.2) used in our previous studies. Chen, Yue; Friedel, Reiner; Henderson, Michael; Claudepierre, Seth; Morley, Steven; Spence, Harlan; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2014 YEAR: 2014 DOI: 10.1002/jgra.v119.310.1002/2013JA019431 Earth\textquoterights outer radiation belt; energetic electrons; Pitch-angle distributions |
|
We have recently conducted a statistical survey on pitch angle distributions of energetic electrons trapped in the Earth\textquoterights outer radiation belt, and a new empirical model was developed based upon survey results. This model\textemdashrelativistic electron pitch angle distribution (REPAD)\textemdashaims to present statistical pictures of electron equatorial pitch angle distributions, instead of the absolute flux levels, as a function of energy, L shell, magnetic local time, and magnetic activity. To quantify and facilitate this statistical survey, we use Legendre polynomials to fit long-term in situ directional fluxes observed near the magnetic equator from three missions: CRRES, Polar, and LANL-97A. As the first of this kind of model, REPAD covers the whole outer belt region, providing not only the mean and median pitch angle distributions in the area but also error estimates of the average distributions. Preliminary verification and validation results demonstrate the reliable performance of this model. Usage of REPAD is mainly to predict the full pitch angle distribution of fluxes along a given magnetic field line, or even on a given drift shell, based upon one single unidirectional or omnidirectional flux measurement anywhere on that field line. This can be particularly useful for data assimilation, which usually has large tolerance on data errors. In addition, relatively small variations in pitch angle distributions measured at L shell between ~ 4 and 5 justify the assumption of fixed pitch angle distributions at GPS equatorial crossings (L ~ 4.2) used in our previous studies. Chen, Y.; Friedel, R.; Henderson, M.; Claudepierre, S.; Morley, S.; Spence, H.; Published by: Journal of Geophysical Research Published on: 03/2014 YEAR: 2014 DOI: 10.1002/2013JA019431 |
|
Resonant scattering of energetic electrons by unusual low-frequency hiss We quantify the resonant scattering effects of the unusual low-frequency dawnside plasmaspheric hiss observed on 30 September 2012 by the Van Allen Probes. In contrast to normal (~100\textendash2000 Hz) hiss emissions, this unusual hiss event contained most of its wave power at ~20\textendash200 Hz. Compared to the scattering by normal hiss, the unusual hiss scattering speeds up the loss of ~50\textendash200 keV electrons and produces more pronounced pancake distributions of ~50\textendash100 keV electrons. It is demonstrated that such unusual low-frequency hiss, even with a duration of a couple of hours, plays a particularly important role in the decay and loss process of energetic electrons, resulting in shorter electron lifetimes for ~50\textendash400 keV electrons than normal hiss, and should be carefully incorporated into global modeling of radiation belt electron dynamics during periods of intense injections. Ni, Binbin; Li, Wen; Thorne, Richard; Bortnik, Jacob; Ma, Qianli; Chen, Lunjin; Kletzing, Craig; Kurth, William; Hospodarsky, George; Reeves, Geoffrey; Spence, Harlan; Blake, Bernard; Fennell, Joseph; Claudepierre, Seth; Published by: Geophysical Research Letters Published on: 03/2014 YEAR: 2014 DOI: 10.1002/2014GL059389 |
|
Spin stabilization design and testing of the Van Allen Probes This paper describes the design decisions taken and the mass properties tracking and testing flow chosen for the Van Allen Probes spacecraft and their deployable systems to achieve the coning angle requirements. Topics include a list of major requirements, a brief description of the error budget, a description of the tracking process of the spacecraft mass properties prior to test, a description of the spin balance and mass properties testing of the spacecraft core and deployable systems, and a presentation of the final mass properties and coning angle calculations of the fully deployed observatories. Launched August 30, 2012, the observed on-orbit, fully deployed configuration coning angles met the requirements, validating the spin balance and mass properties tracking, testing, and calculation methods chosen for the Van Allen Probes mission. Berman, Simmie; Cheng, Weilun; Borowski, Heather; Persons, David; Published by: Published on: 03/2014 YEAR: 2014 DOI: 10.1109/AERO.2014.6836234 |
|
Substorm injected electrons (several\textendash100 s keV) produce whistler-mode chorus waves that are thought to have a major impact on the radiation belts by causing both energization and loss of relativistic electrons in the outer belt. High-altitude measurements, such as those from the Van Allen Probes, provide detailed wave measurements at a few points in the magnetosphere. But physics-based models of radiation-belt dynamics require knowledge of the global distribution of chorus waves. We demonstrate that time-dependent, global distributions of near-equatorial chorus wave intensities can be inferred from low-Earth-orbit (LEO) measurements of precipitating low-energy electrons. We compare in situ observations of near-equatorial chorus waves with LEO observations of precipitating electrons and derive a heuristic formula that relates, quantitatively, electron precipitation fluxes to chorus wave intensities. Finally, we demonstrate how that formula can be applied to LEO precipitation measurements and in situ Van Allen Probes wave measurements to provide global, data-driven inputs for radiation belt models. Chen, Yue; Reeves, Geoffrey; Friedel, Reiner; Cunningham, Gregory; Published by: Geophysical Research Letters Published on: 02/2014 YEAR: 2014 DOI: 10.1002/2013GL059181 |
|
Combining Time History of Events and Macroscale Interaction during Substorms (THEMIS) wave and particle observations and a quantitative calculation of linear wave growth rate, we demonstrate that magnetosonic (MS) waves can be locally excited by ion ring distributions in the Earth\textquoterights magnetosphere when the ion ring energy is comparable to the local Alfven energy. MS waves in association with ion ring distributions were observed by THEMIS A on 24 November 2010 in the afternoon sector, both outside the plasmapause where the wave spectrum varied with fLHR and inside the plasmapause where the wave frequency band remained nearly constant. Our plasma instability analysis in three different regions shows that higher and narrow frequency band MS waves are excited locally outside the plasmapause, and lower and broad frequency band MS waves are excited in the region where the density slightly increases. However, there is no evidence for wave excitation inside the plasmapause, and wave propagation from a distant source is needed to explain their existence. The simulation of the MS wave growth rate spectra during this event agrees reasonably well with the observed wave magnetic field power spectra. We also simulated a MS wave event on 19 October 2011 in the dusk sector and found that the ion ring distribution with an ion ring energy slightly higher than the local Alfven energy can excite the typical broad band MS waves outside the plasmapause. Ma, Qianli; Li, Wen; Chen, Lunjin; Thorne, Richard; Angelopoulos, Vassilis; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2014 YEAR: 2014 DOI: 10.1002/2013JA019591 magnetosonic waves; ring current; THEMIS observation; wave excitation |
| 2013 |
|
Rapid local acceleration of relativistic radiation-belt electrons by magnetospheric chorus Recent analysis of satellite data obtained during the 9 October 2012 geomagnetic storm identified the development of peaks in electron phase space density1, which are compelling evidence for local electron acceleration in the heart of the outer radiation belt2, 3, but are inconsistent with acceleration by inward radial diffusive transport4, 5. However, the precise physical mechanism responsible for the acceleration on 9 October was not identified. Previous modelling has indicated that a magnetospheric electromagnetic emission known as chorus could be a potential candidate for local electron acceleration6, 7, 8, 9, 10, but a definitive resolution of the importance of chorus for radiation-belt acceleration was not possible because of limitations in the energy range and resolution of previous electron observations and the lack of a dynamic global wave model. Here we report high-resolution electron observations11 obtained during the 9 October storm and demonstrate, using a two-dimensional simulation performed with a recently developed time-varying data-driven model12, that chorus scattering explains the temporal evolution of both the energy and angular distribution of the observed relativistic electron flux increase. Our detailed modelling demonstrates the remarkable efficiency of wave acceleration in the Earth\textquoterights outer radiation belt, and the results presented have potential application to Jupiter, Saturn and other magnetized astrophysical objects. Thorne, R.; Li, W.; Ni, B.; Ma, Q.; Bortnik, J.; Chen, L.; Baker, D.; Spence, H.; Reeves, G.; Henderson, M.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Blake, J.; Fennell, J.; Claudepierre, S.; Kanekal, S.; Published by: Nature Published on: 12/2013 YEAR: 2013 DOI: 10.1038/nature12889 |
|
We perform a comprehensive analysis to evaluate hiss-induced scattering effect on the pitch angle evolution and associated decay processes of relativistic electrons. The results show that scattering by the equatorial, highly oblique hiss component is negligible. Quasi-parallel approximation is good for evaluation of hiss-driven electron scattering rates <= 2 MeV. However, realistic wave propagation angles as a function of latitude must be considered to accurately quantify hiss scattering rates above 2 MeV, and ambient plasma density is also a critical parameter. While the first-order cyclotron and the Landau resonances are dominant for hiss scattering < 2 MeV electrons, higher-order resonances become important and even dominant at intermediate pitch angles for ultrarelativistic (>= 3 MeV) electrons. Hiss-induced electron pitch angle evolution shows an initially rapid transport from high to lower pitch angles, with a gradual approach toward equilibrium, and a final exponential decay as a whole. Although hiss scattering rates near the loss cone control the pitch angle evolution and the ultimate loss of ultrarelativistic electrons, the scattering bottleneck significantly affects the loss rate and leads to characteristic top hat-shaped pitch angle distributions at energies < 1 MeV. Decay timescales are on the order of a few days, tens of days, and > 100 days for 500 keV, 2 MeV, and 5 MeV electrons, respectively, consistent with recent observations from the Van Allen Probes and indicating that scattering by hiss can realistically account for the long-term loss process and the pitch angle evolution of relativistic electrons in the plasmasphere following storm time injections. Ni, Binbin; Bortnik, Jacob; Thorne, Richard; Ma, Qianli; Chen, Lunjin; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2013 YEAR: 2013 DOI: 10.1002/2013JA019260 |
|
Excitation of Poloidal standing Alfven waves through the drift resonance wave-particle interaction Drift-resonance wave-particle interaction is a fundamental collisionless plasma process studied extensively in theory. Using cross-spectral analysis of electric field, magnetic field, and ion flux data from the Van Allen Probe (Radiation Belt Storm Probes) spacecraft, we present direct evidence identifying the generation of a fundamental mode standing poloidal wave through drift-resonance interactions in the inner magnetosphere. Intense azimuthal electric field (Eφ) oscillations as large as 10mV/m are observed, associated with radial magnetic field (Br) oscillations in the dawn-noon sector near but south of the magnetic equator at L\~5. The observed wave period, Eφ/Br ratio and the 90\textdegree phase lag between Br and Eφ are all consistent with fundamental mode standing Poloidal waves. Phase shifts between particle fluxes and wave electric fields clearly demonstrate a drift resonance with \~90 keV ring current ions. The estimated earthward gradient of ion phase space density provides a free energy source for wave generation through the drift-resonance instability. A similar drift-resonance process should occur ubiquitously in collisionless plasma systems. One specific example is the \textquotedblleftfishbone\textquotedblright instability in fusion plasma devices. In addition, our observations have important implications for the long-standing mysterious origin of Giant Pulsations. Dai, L.; Takahashi, K; Wygant, J.; Chen, L.; Bonnell, J; Cattell, C.; Thaller, S.; Kletzing, C.; Smith, C.; MacDowall, R.; Baker, D.; Blake, J.; Fennell, J.; Claudepierre, S.; Funsten, H.; Reeves, G.; Spence, H.; Published by: Geophysical Research Letters Published on: 08/2013 YEAR: 2013 DOI: 10.1002/grl.50800 |
|
The HOPE mass spectrometer of the Radiation Belt Storm Probes (RBSP) mission (renamed the Van Allen Probes) is designed to measure the in situ plasma ion and electron fluxes over 4π sr at each RBSP spacecraft within the terrestrial radiation belts. The scientific goal is to understand the underlying physical processes that govern the radiation belt structure and dynamics. Spectral measurements for both ions and electrons are acquired over 1 eV to 50 keV in 36 log-spaced steps at an energy resolution ΔE FWHM/E≈15 \%. The dominant ion species (H+, He+, and O+) of the magnetosphere are identified using foil-based time-of-flight (TOF) mass spectrometry with channel electron multiplier (CEM) detectors. Angular measurements are derived using five polar pixels coplanar with the spacecraft spin axis, and up to 16 azimuthal bins are acquired for each polar pixel over time as the spacecraft spins. Ion and electron measurements are acquired on alternate spacecraft spins. HOPE incorporates several new methods to minimize and monitor the background induced by penetrating particles in the harsh environment of the radiation belts. The absolute efficiencies of detection are continuously monitored, enabling precise, quantitative measurements of electron and ion fluxes and ion species abundances throughout the mission. We describe the engineering approaches for plasma measurements in the radiation belts and present summaries of HOPE measurement strategy and performance. Funsten, H.; Skoug, R.; Guthrie, A.; MacDonald, E.; Baldonado, J.; Harper, R.; Henderson, K.; Kihara, K.; Lake, J.; Larsen, B.; Puckett, A.; Vigil, V.; Friedel, R.; Henderson, M.; Niehof, J.; Reeves, G.; Thomsen, M.; Hanley, J.; George, D.; Jahn, J.-M.; Cortinas, S.; Santos, Los; Dunn, G.; Edlund, E.; Ferris, M.; Freeman, M.; Maple, M.; Nunez, C.; Taylor, T.; Toczynski, W.; Urdiales, C.; Spence, H.; Cravens, J.; Suther, L.; Chen, J.; Published by: Space Science Reviews Published on: 08/2013 YEAR: 2013 DOI: 10.1007/s11214-013-9968-7 |
| 2012 |
|
1] The temporal and spatial development of the ring current is evaluated during the 23\textendash26 October 2002 high-speed stream (HSS) storm, using a kinetic ring current-atmosphere interactions model with self-consistent magnetic field (RAM-SCB). The effects of nondipolar magnetic field configuration are investigated on both ring current ion and electron dynamics. As the self-consistent magnetic field is depressed at large (>4RE) radial distances on the nightside during the storm main phase, the particles\textquoteright drift velocities increase, the ion and electron fluxes are reduced and the ring current is confined closer to Earth. In contrast to ions, the electron fluxes increase closer to Earth and the fractional electron energy reaches \~20\% near storm peak due to better electron trapping in a nondipolar magnetic field. The ring current contribution to Dst calculated using Biot-Savart integration differs little from the DPS relation except during quiet time. RAM-SCB simulations underestimate |SYM-H| minimum by \~25\% but reproduce very well the storm recovery phase. Increased anisotropies develop in the ion and electron velocity distributions in a self-consistent magnetic field due to energy dependent drifts, losses, and dispersed injections. There is sufficient free energy to excite whistler mode chorus, electromagnetic ion cyclotron (EMIC), and magnetosonic waves in the equatorial magnetosphere. The linear growth rate of whistler mode chorus intensifies in the postmidnight to noon sector, EMIC waves are predominantly excited in the afternoon to midnight sector, and magnetosonic waves are excited over a broad MLT range both inside and outside the plasmasphere. The wave growth rates in a dipolar magnetic field have significantly smaller magnitude and spatial extent. Jordanova, V.; Welling, D.; Zaharia, S.; Chen, L.; Thorne, R.; Published by: Journal of Geophysical Research Published on: 09/2012 YEAR: 2012 DOI: 10.1029/2011JA017433 |
|
Weak turbulence in the magnetosphere: Formation of whistler wave cavity by nonlinear scattering We consider the weak turbulence of whistler waves in the in low-β inner magnetosphere of the earth. Whistler waves, originating in the ionosphere, propagate radially outward and can trigger nonlinear induced scattering by thermal electrons provided the wave energy density is large enough. Nonlinear scattering can substantially change the direction of the wave vector of whistler waves and hence the direction of energy flux with only a small change in the frequency. A portion of whistler waves return to the ionosphere with a smaller perpendicular wave vector resulting in diminished linear damping and enhanced ability to pitch-angle scatter trapped electrons. In addition, a portion of the scatteredwave packets can be reflected near the ionosphere back into the magnetosphere. Through multiple nonlinear scatterings and ionospheric reflections a long-lived wavecavity containing turbulent whistler waves can be formed with the appropriate properties to efficiently pitch-angle scatter trapped electrons. The primary consequence on the earth\textquoterights radiation belts is to reduce the lifetime of the trapped electron population. Crabtree, C.; Rudakov, L.; Ganguli, G.; Mithaiwala, M.; Galinsky, V.; Shevchenko, V.; Published by: Physics of Plasmas Published on: 01/2012 YEAR: 2012 DOI: 10.1063/1.3692092 |
| 2007 |
|
The energization of relativistic electrons in the outer Van Allen radiation belt The origin and dynamics of the Van Allen radiation belts is one of the longest-standing questions of the space age, and one that is increasingly important for space applications as satellite systems become more sophisticated, smaller and more susceptible to radiation effects. The precise mechanism by which the Earth\textquoterights magnetosphere is able to accelerate electrons from thermal to ultrarelativistic energies (Edouble greater than0.5 MeV) has been particularly difficult to definitively resolve. The traditional explanation is that large-scale, fluctuating electric and magnetic fields energize particles through radial diffusion1. More recent theories2, 3 and observations4, 5 have suggested that gyro-resonant wave\textendashparticle interactions may be comparable to or more important than radial diffusion. Using data collected simultaneously by multiple satellites passing through the magnetosphere at different distances from the Earth, we demonstrate that the latter of these is the dominant mechanism responsible for relativistic electron acceleration. Specifically, we identify frequent and persistent peaks in equatorial electron phase space density near or inside geosynchronous orbit that provide unambiguous evidence for local wave\textendashparticle acceleration. These observations represent an important step towards a more complete physical understanding of radiation belt dynamics and to the development of space-weather models. Chen, Yue; Reeves, Geoffrey; Friedel, Reiner; Published by: Nature Physics Published on: 09/2007 YEAR: 2007 DOI: 10.1038/nphys655 |