Bibliography
|
Notice:
|
Found 29 entries in the Bibliography.
Showing entries from 1 through 29
| 2019 |
|
A statistical study was conducted of Earth\textquoterights radiation belt electron response to geomagnetic storms using NASA\textquoterights Van Allen Probes mission. Data for electrons with energies ranging from 30 keV to 6.3 MeV were included and examined as a function of L-shell, energy, and epoch time during 110 storms with SYM-H <=-50 nT during September 2012 to September 2017 (inclusive). The radiation belt response revealed clear energy and L-shell dependencies, with tens of keV electrons enhanced at all L-shells (2.5 <= L <= 6) in all storms during the storm commencement and main phase and then quickly decaying away during the early recovery phase, low hundreds of keV electrons enhanced at lower L-shells (~3 <= L <= ~4) in upward of 90\% of all storms and then decaying gradually during the recovery phase, and relativistic electrons throughout the outer belt showing main phase dropouts with subsequent and generally unpredictable levels of replenishment during the recovery phase. Compared to prestorm levels, electrons with energies >1 MeV also revealed a marked increase in likelihood of a depletion at all L-shells through the outer belt (3.5 <= L <= 6). Additional statistics were compiled revealing the storm time morphology of the radiation belts, confirming the aforementioned qualitative behavior. Considering storm drivers in the solar wind: storms driven by coronal mass ejection (CME) shocks/sheaths and CME ejecta only are most likely to result in a depletion of >1-MeV electrons throughout the outer belt, while storms driven by full CMEs and stream interaction regions are most likely to produce an enhancement of MeV electrons at lower (L < ~5) and higher (L > ~4.5) L-shells, respectively. CME sheaths intriguingly result in a distinct enhancement of ~1-MeV electrons around L~5.5, and on average, CME sheaths and stream interaction regions result in double outer belt structures. Turner, D.; Kilpua, E.; Hietala, H.; Claudepierre, S.; O\textquoterightBrien, T.; Fennell, J.; Blake, J.; Jaynes, A.; Kanekal, S.; Baker, D.; Spence, H.; Ripoll, J.-F.; Reeves, G.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2019 YEAR: 2019 DOI: 10.1029/2018JA026066 energetic particles; Geomagnetic storms; inner magnetosphere; Radiation belts; relativistic electrons; Van Allen Probes; wave-particle interactions |
|
We describe a new, more accurate procedure for estimating and removing inner zone background contamination from Van Allen Probes Magnetic Electron Ion Spectrometer (MagEIS) radiation belt measurements. This new procedure is based on the underlying assumption that the primary source of background contamination in the electron measurements at L shells less than three, energetic inner belt protons, is relatively stable. Since a magnetic spectrometer can readily distinguish between foreground electrons and background signals, we are able to exploit the proton stability to construct a model of the background contamination in each MagEIS detector by only considering times when the measurements are known to be background dominated. We demonstrate, for relativistic electron measurements in the inner zone, that the new technique is a significant improvement upon the routine background corrections that are used in the standard MagEIS data processing, which can \textquotedblleftovercorrect\textquotedblright and therefore remove real (but small) electron fluxes. As an example, we show that the previously reported 1-MeV injection into the inner zone that occurred in June of 2015 was distributed more broadly in L and persisted in the inner zone longer than suggested by previous estimates. Such differences can have important implications for both scientific studies and spacecraft engineering applications that make use of MagEIS electron data in the inner zone at relativistic energies. We compare these new results with prior work and present more recent observations that also show a 1-MeV electron injection into the inner zone following the September 2017 interplanetary shock passage. Claudepierre, S.; O\textquoterightBrien, T.; Looper, M.; Blake, J.; Fennell, J.; Roeder, J.; Clemmons, J.; Mazur, J.; Turner, D.; Reeves, G.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2019 YEAR: 2019 DOI: 10.1029/2018JA026349 Inner zone; particle detectors; Radiation belt; relativistic electrons; Slot region; Space weather; Van Allen Probes |
| 2018 |
|
Electron flux measurements are an important diagnostic for interactions between ultralow-frequency (ULF) waves and relativistic (\~1 MeV) electrons. Since measurements are collected by particle detectors with finite energy channel width, they are affected by a phase mixing process that can obscure these interactions. We demonstrate that ultrahigh-resolution electron measurements from the Magnetic Electron Ion Spectrometer on the Van Allen Probes mission\textemdashobtained using a data product that improves the energy resolution by roughly an order of magnitude\textemdashare crucial for understanding ULF wave-particle interactions. In particular, the ultrahigh-resolution measurements reveal a range of complex dynamics that cannot be resolved by standard measurements. Furthermore, the standard measurements provide estimates for the ULF flux modulation amplitude, period, and phase that may not be representative of true flux modulations, potentially leading to ambiguous conclusions concerning electron dynamics. Hartinger, M.; Claudepierre, S.; Turner, D.; Reeves, G.; Breneman, A.; Mann, I.; Peek, T.; Chang, E.; Blake, J.; Fennell, J.; O\textquoterightBrien, T.; Looper, M.; Published by: Geophysical Research Letters Published on: 10/2018 YEAR: 2018 DOI: 10.1029/2018GL080291 drift resonance; particle detector; Pc5; Radiation belts; ULF wave; Van Allen Probes; Wave-particle interaction |
|
We explore the penetration of >60 MeV protons into the magnetosphere during the 10\textendash14 September 2017 solar energetic particle event. Solar energetic particles can cause single event effects and total dose degradation in spacecraft electronics. Therefore, it is important for satellite anomaly analysis to understand how deep into the magnetosphere these particles penetrate. Whereas most studies of geomagnetic cutoffs use low-altitude data, we use data from the Relativistic Proton Spectrometer on National Aeronautics and Space Administration\textquoterights Van Allen Probes, which is in a high-altitude, elliptical orbit. We determine how the penetration depends on particle energy, location, and direction of incidence. We evaluate multiple published models of the geomagnetic cutoff to determine how well these models constrain the spectrum at the location of a spacecraft inside the magnetosphere given data outside the magnetosphere. We show that, compared to cutoff models, low-altitude proton measurements are far superior for near-real-time monitoring of the geomagnetic cutoff in support of high-altitude anomaly resolution. O\textquoterightBrien, T.; Mazur, J.; Looper, M.; Published by: Space Weather Published on: 08/2018 YEAR: 2018 DOI: 10.1029/2018SW001960 east-west effect; geomagnetic cutoffs; solar particle event; Van Allen Probes |
|
Evidence of Microbursts Observed Near the Equatorial Plane in the Outer Van Allen Radiation Belt We present the first evidence of electron microbursts observed near the equatorial plane in Earth\textquoterights outer radiation belt. We observed the microbursts on March 31st, 2017 with the Magnetic Electron Ion Spectrometer and RBSP Ion Composition Experiment on the Van Allen Probes. Microburst electrons with kinetic energies of 29-92 keV were scattered over a substantial range of pitch angles, and over time intervals of 150-500 ms. Furthermore, the microbursts arrived without dispersion in energy, indicating that they were recently scattered near the spacecraft. We have applied the relativistic theory of wave-particle resonant diffusion to the calculated phase space density, revealing that the observed transport of microburst electrons is not consistent with the hypothesized quasi-linear approximation. Shumko, Mykhaylo; Turner, Drew; O\textquoterightBrien, T.; Claudepierre, Seth; Sample, John; Hartley, D.; Fennell, Joseph; Blake, Bernard; Gkioulidou, Matina; Mitchell, Donald; Published by: Geophysical Research Letters Published on: 07/2018 YEAR: 2018 DOI: 10.1029/2018GL078451 |
| 2017 |
|
Spatial Scale and Duration of One Microburst Region on 13 August 2015 Prior studies of microburst precipitation have largely relied on estimates of the spatial scale and temporal duration of the microburst region in order to determine the radiation belt loss rate of relativistic electrons. These estimates have often relied on the statistical distribution of microburst events. However, few studies have directly observed the spatial and temporal evolution of a single microburst event. In this study, we combine BARREL balloon-borne X-ray measurements with FIREBIRD-II and AeroCube-6 CubeSat electron measurements to determine the spatial and temporal evolution of a microburst region in the morning MLT sector on 13 August 2015. The microburst region is found to extend across at least four hours in local time in the morning sector, from 09:00 to 13:00 MLT, and from L of 5 out to 10. The microburst event lasts for nearly nine hours. Smaller scale structure is investigated using the dual AeroCube-6 CubeSats, and is found to be consistent with the spatial size of whistler mode chorus wave observations near the equatorial plane. Anderson, B.; Shekhar, S.; Millan, R.; Crew, A.; Spence, H.; Klumpar, D.; Blake, J.; O\textquoterightBrien, T.; Turner, D.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2017 YEAR: 2017 DOI: 10.1002/2016JA023752 Microbursts; Radiation Belt Dynamics; Van Allen Probes; whistler mode chorus waves |
|
The hidden dynamics of relativistic electrons (0.7-1.5~MeV) in the inner zone and slot region We present measurements of relativistic electrons (0.7\textendash1.5 MeV) in the inner zone and slot region obtained by the Magnetic Electron and Ion Spectrometer (MagEIS) instrument on Van Allen Probes. The data presented are corrected for background contamination, which is primarily due to inner-belt protons in these low-L regions. We find that \~1 MeV electrons were transported into the inner zone following the two largest geomagnetic storms of the Van Allen Probes era to date, the March and June 2015 events. As \~1 MeV electrons were not observed in Van Allen Probes data in the inner zone prior to these two events, the injections created a new inner belt that persisted for at least 1.5 years. In contrast, we find that electrons injected into the slot region decay on much faster timescales, approximately tens of days. Furthermore, we find no evidence of >1.5 MeV electrons in the inner zone during the entire time interval considered (April 2013 through September 2016). The energies we examine thus span a transition range in the steeply falling inner zone electron spectrum, where modest intensities are observed at 0.7 MeV, and no electrons are observed at 1.5 MeV. To validate the results obtained from the background corrected flux measurements, we also present detailed pulse-height spectra from individual MagEIS detectors. These measurements confirm our results and also reveal low-intensity inner zone and slot region electrons that are not captured in the standard background corrected data product. Finally, we briefly discuss efforts to refine the upper limit of inner zone MeV electron flux obtained in earlier work. Claudepierre, S.; O\textquoterightBrien, T.; Fennell, J.; Blake, J.; Clemmons, J.; Looper, M.; Mazur, J.; Roeder, J.; Turner, D.; Reeves, G.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2017 YEAR: 2017 DOI: 10.1002/2016JA023719 Inner zone; particle detectors; Radiation belt; relativistic electrons; Slot region; Space weather; Van Allen Probes |
|
The hidden dynamics of relativistic electrons (0.7-1.5~MeV) in the inner zone and slot region We present measurements of relativistic electrons (0.7\textendash1.5 MeV) in the inner zone and slot region obtained by the Magnetic Electron and Ion Spectrometer (MagEIS) instrument on Van Allen Probes. The data presented are corrected for background contamination, which is primarily due to inner-belt protons in these low-L regions. We find that \~1 MeV electrons were transported into the inner zone following the two largest geomagnetic storms of the Van Allen Probes era to date, the March and June 2015 events. As \~1 MeV electrons were not observed in Van Allen Probes data in the inner zone prior to these two events, the injections created a new inner belt that persisted for at least 1.5 years. In contrast, we find that electrons injected into the slot region decay on much faster timescales, approximately tens of days. Furthermore, we find no evidence of >1.5 MeV electrons in the inner zone during the entire time interval considered (April 2013 through September 2016). The energies we examine thus span a transition range in the steeply falling inner zone electron spectrum, where modest intensities are observed at 0.7 MeV, and no electrons are observed at 1.5 MeV. To validate the results obtained from the background corrected flux measurements, we also present detailed pulse-height spectra from individual MagEIS detectors. These measurements confirm our results and also reveal low-intensity inner zone and slot region electrons that are not captured in the standard background corrected data product. Finally, we briefly discuss efforts to refine the upper limit of inner zone MeV electron flux obtained in earlier work. Claudepierre, S.; O\textquoterightBrien, T.; Fennell, J.; Blake, J.; Clemmons, J.; Looper, M.; Mazur, J.; Roeder, J.; Turner, D.; Reeves, G.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2017 YEAR: 2017 DOI: 10.1002/2016JA023719 Inner zone; particle detectors; Radiation belt; relativistic electrons; Slot region; Space weather; Van Allen Probes |
|
Using observations from NASA\textquoterights Van Allen Probes, we study the role of sudden particle enhancements at low L shells (SPELLS) as a source of inner radiation belt electrons. SPELLS events are characterized by electron intensity enhancements of approximately an order of magnitude or more in less than 1 day at L < 3. During quiet and average geomagnetic conditions, the phase space density radial distributions for fixed first and second adiabatic invariants are peaked at 2 < L < 3 for electrons ranging in energy from ~50 keV to ~1 MeV, indicating that slow inward radial diffusion is not the dominant source of inner belt electrons under quiet/average conditions. During SPELLS events, the evolution of electron distributions reveals an enhancement of phase space density that can exceed 3 orders of magnitude in the slot region and continues into the inner radiation belt, which is evidence that these events are an important\textemdashand potentially dominant\textemdashsource of inner belt electrons. Electron fluxes from September 2012 through February 2016 reveal that SPELLS occur frequently (~2.5/month at 200 keV), but the number of observed events decreases exponentially with increasing electron energy for >=100 keV. After SPELLS events, the slot region reforms due to slow energy-dependent decay over several day time scales, consistent with losses due to interactions with plasmaspheric hiss. Combined, these results indicate that the peaked phase space density distributions in the inner electron radiation belt result from an \textquotedbllefton/off,\textquotedblright geomagnetic-activity-dependent source from higher radial distances. Turner, D.; O\textquoterightBrien, T.; Fennell, J.; Claudepierre, S.; Blake, J.; Jaynes, A.; Baker, D.; Kaneka, S.; Gkioulidou, M.; Henderson, M.; Reeves, G.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2017 YEAR: 2017 DOI: 10.1029/1999JA900445 energetic particle injections; inner magnetosphere; Radiation belts; relativistic electrons; Van Allen Probes |
| 2016 |
|
Using observations from NASA\textquoterights Van Allen Probes, we study the role of sudden particle enhancements at low L-shells (SPELLS) as a source of inner radiation belt electrons. SPELLS events are characterized by electron intensity enhancements of approximately an order of magnitude or more in less than one day at L < 3. During quiet and average geomagnetic conditions, the phase space density radial distributions for fixed first and second adiabatic invariants are peaked at 2 < L < 3 for electrons ranging in energy from ~50 keV to ~1 MeV, indicating that slow inward radial diffusion is not the dominant source of inner belt electrons under quiet/average conditions. During SPELLS events, the evolution of electron distributions reveals an enhancement of phase space density that can exceed three orders of magnitude in the slot region and continues into the inner radiation belt, which is evidence that these events are an important - and potentially dominant - source of inner belt electrons. Electron fluxes from September 2012 through February 2016 reveal that SPELLS occur frequently (~2.5/month at 200 keV), but the number of observed events decreases exponentially with increasing electron energy for >=100 keV. After SPELLS events, the slot region reforms due to slow energy-dependent decay over several day timescales, consistent with losses due to interactions with plasmaspheric hiss. Combined, these results indicate that the peaked phase space density distributions in the inner electron radiation belt result from an \textquotedbllefton/off\textquotedblright, geomagnetic-activity-dependent source from higher radial distances. Turner, D.; O\textquoterightBrien, T.; Fennell, J.; Claudepierre, S.; Blake, J.; Jaynes, A.; Baker, D.; Kanekal, S.; Gkioulidou, M.; Henderson, M.; Reeves, G.; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2016 YEAR: 2016 DOI: 10.1002/2016JA023600 2720 Energetic Particles; trapped; 2730 Magnetosphere: inner; 2774 Radiation belts; 7807 Charged particle motion and acceleration; 7984 Space radiation environment; energetic particle injections; inner magnetosphere; Radiation belts; relativistic electrons; Van Allen Probes |
|
Current energetic particle sensors Several energetic particle sensors designed to make measurements in the current decade are described and their technology and capabilities discussed and demonstrated. Most of these instruments are already on orbit or approaching launch. These include the Magnetic Electron Ion Spectrometers (MagEIS) and the Relativistic Electron Proton Telescope (REPT) that are flying on the Van Allen Probes, the Fly\textquoterights Eye Electron Proton Spectrometers (FEEPS) flying on the Magnetospheric Multiscale (MMS) mission, and Dosimeters flying on the AC6 Cubesat mission. We focus mostly on the electron measurement capability of these sensors while providing summary comments of their ion measurement capabilities if they have any. Fennell, J.; Blake, J.; Claudepierre, S.; Mazur, J.; Kanekal, S.; O\textquoterightBrien, P.; Baker, D.; Crain, W.; Mabry, D.; Clemmons, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2016 YEAR: 2016 DOI: 10.1002/2016JA022588 |
|
Inner zone and slot electron radial diffusion revisited Using recent data from NASA\textquoterights Van Allen Probes, we estimate the quiet time radial diffusion coefficients for electrons in the inner radiation belt (L < 3) with energies from ~50 to 750 keV. The observations are consistent with dynamics dominated by pitch angle scattering and radial diffusion. We use a coordinate system in which these two modes of diffusion are separable. Then we integrate phase space density over pitch angle to obtain a \textquotedblleftbundle content\textquotedblright that is invariant to pitch angle scattering, except for atmospheric loss. We estimate the effective radial diffusion coefficient from the temporal and radial variation of the bundle content. We show that our diffusion coefficients agree well with previously determined values obtained in the 1960s and 1970s and follow the form one expects for radial diffusion caused by exponentially decaying impulses in the large-scale electrostatic potential. O\textquoterightBrien, T.; Claudepierre, S.; Guild, T.; Fennell, J.; Turner, D.; Blake, J.; Clemmons, J.; Roeder, J.; Published by: Geophysical Research Letters Published on: 07/2016 YEAR: 2016 DOI: 10.1002/2016GL069749 Inner zone; radial diffusion; Radiation belt; Van Allen Probes |
| 2015 |
|
The effects of geomagnetic storms on electrons in Earth\textquoterights radiation belts We use Van Allen Probes data to investigate the responses of 10s of keV to 2 MeV electrons throughout a broad range of the radiation belts (2.5 <= L <= 6.0) during 52 geomagnetic storms from the most recent solar maximum. Electron storm-time responses are highly dependent on both electron energy and L-shell. 10s of keV electrons typically have peak fluxes in the inner belt or near-Earth plasma sheet and fill the inner magnetosphere during storm main phases. ~100 to ~600 keV electrons are enhanced in up to 87\% of cases around L~3.7, and their peak flux location moves to lower L-shells during storm recovery phases. Relativistic electrons (>=~1 MeV) are nearly equally likely to produce enhancement, depletion, and no-change events in the outer belt. We also show that the L-shell of peak flux correlates to storm magnitude only for 100s of keV electrons. Turner, D.; O\textquoterightBrien, T.; Fennell, J.; Claudepierre, S.; Blake, J.; Kilpua, E.; Hietala, H.; Published by: Geophysical Research Letters Published on: 07/2015 YEAR: 2015 DOI: 10.1002/2015GL064747 electrons; Van Allen Probes; Geomagnetic storms; Radiation belts |
|
A background correction algorithm for Van Allen Probes MagEIS electron flux measurements We describe an automated computer algorithm designed to remove background contamination from the Van Allen Probes MagEIS electron flux measurements. We provide a detailed description of the algorithm with illustrative examples from on-orbit data. We find two primary sources of background contamination in the MagEIS electron data: inner zone protons and bremsstrahlung X-rays generated by energetic electrons interacting with the spacecraft material. Bremsstrahlung X-rays primarily produce contamination in the lower energy MagEIS electron channels (~30-500 keV) and in regions of geospace where multi-MeV electrons are present. Inner zone protons produce contamination in all MagEIS energy channels at roughly L < 2.5. The background corrected MagEIS electron data produce a more accurate measurement of the electron radiation belts, as most earlier measurements suffer from unquantifiable and uncorrectable contamination in this harsh region of the near-Earth space environment. These background-corrected data will also be useful for spacecraft engineering purposes, providing ground truth for the near-Earth electron environment and informing the next generation of spacecraft design models (e.g., AE9). Claudepierre, S.; O\textquoterightBrien, T.; Blake, J.; Fennell, J.; Roeder, J.; Clemmons, J.; Looper, M.; Mazur, J.; Mulligan, T.; Spence, H.; Reeves, G.; Friedel, R.; Henderson, M.; Larsen, B.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2015 YEAR: 2015 DOI: 10.1002/2015JA021171 Background contamination; Inner radiation belt; outer radiation belt; Particle measurements; Radiation belt; Spacecraft engineering; Van Allen Probes |
|
Release of AE9/AP9/SPM Radiation Belt and Space Plasma Model Version 1.20.002 Johnston, Wm.; O\textquoterightBrien, Paul; Ginet, Gregory; Published by: Space Weather Published on: 05/2015 YEAR: 2015 DOI: 10.1002/2015SW001212 |
|
On the use of drift echoes to characterize on-orbit sensor discrepancies We describe a method for using drift echo signatures in on-orbit data to resolve discrepancies between different measurements of particle flux. The drift period has a well-defined energy dependence, which gives rise to time dispersion of the echoes. The dispersion can then be used to determine the effective energy for one or more channels given each channel\textquoterights drift period and the known energy for a reference channel. We demonstrate this technique on multiple instruments from the Van Allen probes mission. Drift echoes are only easily observed at high energies (100s keV to multiple MeV), where several drift periods occur before the observing satellite has moved on or the global magnetic conditions have changed. We describe a first-order correction for spacecraft motion. The drift echo technique has provided a significant clue in resolving substantial flux discrepancies between two instruments measuring fluxes near 2 MeV. O\textquoterightBrien, T.P.; Claudepierre, S.G.; Looper, M.D.; Blake, J.B.; Fennell, J.F.; Clemmons, J.H.; Roeder, J.L.; Kanekal, S.G.; Manweiler, J.W.; Mitchell, D.G.; Gkioulidou, M.; Lanzerotti, L.J.; Spence, H.E.; Reeves, G.D.; Baker, D.N.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2015 YEAR: 2015 DOI: 10.1002/2014JA020859 |
|
Van Allen Probes show the inner radiation zone contains no MeV electrons: ECT/MagEIS data We present Van Allen Probe observations of electrons in the inner radiation zone. The measurements were made by the ECT/MagEIS sensors that were designed to measure electrons with the ability to remove unwanted signals from penetrating protons, providing clean measurements. No electrons >900 keV were observed with equatorial fluxes above background (i.e. >0.1 electrons/(cm2 s sr keV)) in the inner zone. The observed fluxes are compared to the AE9 model and CRRES observations. Electron fluxes <200 keV exceeded the AE9 model 50\% fluxes and were lower than the higher energy model fluxes. Phase space density radial profiles for 1.3<=L*<2.5 had mostly positive gradients except near L*~2.1 where the profiles for μ = 20-30 MeV/G were flat or slightly peaked. The major result is that MagEIS data do not show the presence of significant fluxes of MeV electrons in the inner zone while current radiation belt models and previous publications do. Fennell, J.; Claudepierre, S.; Blake, J.; O\textquoterightBrien, T.; Clemmons, J.; Baker, D.; Spence, H.; Reeves, G.; Published by: Geophysical Research Letters Published on: 02/2015 YEAR: 2015 DOI: 10.1002/2014GL062874 inner magnetosphere; Inner radiation belt; Inner zone; trapped electrons; Van Allen Probes |
|
Energetic electron injections deep into the inner magnetosphere associated with substorm activity From a survey of the first nightside season of NASA\textquoterights Van Allen Probes mission (Dec/2012 \textendash Sep/2013), 47 energetic (10s to 100s of keV) electron injection events were found at L-shells <= 4, all of which are deeper than any previously reported substorm-related injections. Preliminary details from these events are presented, including how: all occurred shortly after dipolarization signatures and injections were observed at higher L-shells; the deepest observed injection was at L~2.5; and, surprisingly, L<=4 injections are limited in energy to <=250 keV. We present a detailed case study of one example event revealing that the injection of electrons down to L~3.5 was different from injections observed at higher L and likely resulted from drift resonance with a fast magnetosonic wave in the Pi 2 frequency range inside the plasmasphere. These observations demonstrate that injections occur at very low L-shells and may play an important role for inner zone electrons. Turner, D.; Claudepierre, S.; Fennell, J.; O\textquoterightBrien, T.; Blake, J.; Lemon, C.; Gkioulidou, M.; Takahashi, K.; Reeves, G.; Thaller, S.; Breneman, A.; Wygant, J.; Li, W.; Runov, A.; Angelopoulos, V.; Published by: Geophysical Research Letters Published on: 02/2015 YEAR: 2015 DOI: 10.1002/2015GL063225 energetic particle injections; inner magnetosphere; Radiation belts; substorms; THEMIS; Van Allen Probes |
| 2014 |
|
Asymmetries in the magnetospheric magnetic field produce drift shell splitting, which causes the radial (drift shell) invariant to sometimes depend on pitch angle. Where drift shell splitting is significant, pitch angle scattering leads to diffusion in all three invariants of the particle\textquoterights motion, including cross diffusion. We examine the magnitude of drift shell splitting-related anomalous diffusion for outer zone electrons compared to conventional diffusion in the absence of drift shell splitting. We assume the primary local scattering process is wave-particle interactions with chorus. We find that anomalous radial diffusion can exceed that of conventional drift resonant radial diffusion for particles with energies near 0.1 MeV at all radial distances outside the plasmasphere during quiet to moderate geomagnetic activity and, it is significant at 0.5 MeV. Cross diffusion involving the radial invariant can exceed the geometric mean of the corresponding pure diffusion coefficients at 0.1 MeV, and that such cross diffusion is significant even at 0.5-1 MeV. At 1 MeV, cross diffusion is often significant. The highest radial distances and magnetic activity levels in our study do not always exhibit as much significant anomalous diffusion as moderate radial distances and activity levels. This can be explained by (a) stronger dependence of conventional diffusion on magnetic activity and radius, and (b) strongest drift shell splitting at moderate magnetic activity. Simulation codes that neglect the possibility for cross terms will likely systematically underperform, especially for 0.1-0.5 MeV electrons, for much of the outer zone for quiet to moderate levels of magnetic activity. Published by: Journal of Geophysical Research: Space Physics Published on: 12/2014 YEAR: 2014 DOI: 10.1002/2014JA020422 |
|
We report large directional anisotropies of >60 MeV protons using instrumentation on the Van Allen Probes. The combination of a spinning satellite and measurements from the Relativistic Proton Spectrometer instruments that are insensitive to protons outside the instrument field of view together yield a new look at proton radial gradients. The relatively large proton gyroradius at 60 MeV couples with the radial gradients to produce large (maximum ~10:1) flux anisotropies depending on (i) whether the proton guiding center was above or below the Van Allen Probes spacecraft and (ii) the sign of the local flux gradient. In addition to these newly measured anisotropies, below ~2000 km we report a new effect of systematically changing minimum altitude on some proton drift shells that further modulates the anisotropy caused by the atmosphere. This discovery may offer a new way of monitoring changes to the loss of inner belt protons into the Earth\textquoterights atmosphere. Mazur, J.; O\textquoterightBrien, T.; Looper, M.; Blake, J.; Published by: Geophysical Research Letters Published on: 06/2014 YEAR: 2014 DOI: 10.1002/grl.v41.1110.1002/2014GL060029 |
|
Using data from NASA\textquoterights Van Allen Probes, we have identified a synchronized exponential decay of electron flux in the outer zone, near L* = 5.0. Exponential decays strongly indicate the presence of a pure eigenmode of a diffusion operator acting in the synchronized dimension(s). The decay has a time scale of about 4 days with no dependence on pitch angle. While flux at nearby energies and L* is also decaying exponentially, the decay time varies in those dimensions. This suggests the primary decay mechanism is elastic pitch angle scattering, which itself depends on energy and L*. We invert the shape of the observed eigenmode to obtain an approximate shape of the pitch angle diffusion coefficient and show excellent agreement with diffusion by plasmaspheric hiss. Our results suggest that empirically derived eigenmodes provide a powerful diagnostic of the dynamic processes behind exponential decays. O\textquoterightBrien, T.; Claudepierre, S.; Blake, J.; Fennell, J.; Clemmons, J.; Roeder, J.; Spence, H.; Reeves, G.; Baker, D.; Published by: Geophysical Research Letters Published on: 01/2014 YEAR: 2014 DOI: 10.1002/2013GL058713 |
| 2013 |
|
The radiation belts and plasma in the Earth\textquoterights magnetosphere pose hazards to satellite systems which restrict design and orbit options with a resultant impact on mission performance and cost. For decades the standard space environment specification used for spacecraft design has been provided by the NASA AE8 and AP8 trapped radiation belt models. There are well-known limitations on their performance, however, and the need for a new trapped radiation and plasma model has been recognized by the engineering community for some time. To address this challenge a new set of models, denoted AE9/AP9/SPM, for energetic electrons, energetic protons and space plasma has been developed. The new models offer significant improvements including more detailed spatial resolution and the quantification of uncertainty due to both space weather and instrument errors. Fundamental to the model design, construction and operation are a number of new data sets and a novel statistical approach which captures first order temporal and spatial correlations allowing for the Monte-Carlo estimation of flux thresholds for user-specified percentile levels (e.g., 50th and 95th) over the course of the mission. An overview of the model architecture, data reduction methods, statistics algorithms, user application and initial validation is presented in this paper. Ginet, G.; textquoterightBrien, T.; Huston, S.; Johnston, W.; Guild, T.; Friedel, R.; Lindstrom, C.; Roth, C.; Whelan, P.; Quinn, R.; Madden, D.; Morley, S.; Su, Yi-Jiun; Published by: Space Science Reviews Published on: 11/2013 YEAR: 2013 DOI: 10.1007/s11214-013-9964-y |
|
This paper describes the Magnetic Electron Ion Spectrometer (MagEIS) instruments aboard the RBSP spacecraft from an instrumentation and engineering point of view. There are four magnetic spectrometers aboard each of the two spacecraft, one low-energy unit (20\textendash240 keV), two medium-energy units (80\textendash1200 keV), and a high-energy unit (800\textendash4800 keV). The high unit also contains a proton telescope (55 keV\textendash20 MeV). The magnetic spectrometers focus electrons within a selected energy pass band upon a focal plane of several silicon detectors where pulse-height analysis is used to determine if the energy of the incident electron is appropriate for the electron momentum selected by the magnet. Thus each event is a two-parameter analysis, an approach leading to a greatly reduced background. The physics of these instruments are described in detail followed by the engineering implementation. The data outputs are described, and examples of the calibration results and early flight data presented. Blake, J.; Carranza, P.; Claudepierre, S.; Clemmons, J.; Crain, W.; Dotan, Y.; Fennell, J.; Fuentes, F.; Galvan, R.; George, J.; Henderson, M.; Lalic, M.; Lin, A; Looper, M.; Mabry, D.; Mazur, J.; McCarthy, B.; Nguyen, C.; textquoterightBrien, T.; Perez, M.; Redding, M.; Roeder, J.; Salvaggio, D.; Sorensen, G.; Spence, H.; Yi, S.; Zakrzewski, M.; Published by: Space Science Reviews Published on: 11/2013 YEAR: 2013 DOI: 10.1007/s11214-013-9991-8 |
|
The Relativistic Proton Spectrometer (RPS) for the Radiation Belt Storm Probes Mission The Relativistic Proton Spectrometer (RPS) on the Radiation Belt Storm Probes spacecraft is a particle spectrometer designed to measure the flux, angular distribution, and energy spectrum of protons from \~60 MeV to \~2000 MeV. RPS will investigate decades-old questions about the inner Van Allen belt proton environment: a nearby region of space that is relatively unexplored because of the hazards of spacecraft operation there and the difficulties in obtaining accurate proton measurements in an intense penetrating background. RPS is designed to provide the accuracy needed to answer questions about the sources and losses of the inner belt protons and to obtain the measurements required for the next-generation models of trapped protons in the magnetosphere. In addition to detailed information for individual protons, RPS features count rates at a 1-second timescale, internal radiation dosimetry, and information about electrostatic discharge events on the RBSP spacecraft that together will provide new information about space environmental hazards in the Earth\textquoterights magnetosphere. Mazur, J.; Friesen, L.; Lin, A.; Mabry, D.; Katz, N.; Dotan, Y.; George, J.; Blake, J.; LOOPER, M; Redding, M.; textquoterightBrien, T.; Cha, J.; Birkitt, A.; Carranza, P.; Lalic, M.; Fuentes, F.; Galvan, R.; McNab, M.; Published by: Space Science Reviews Published on: 11/2013 YEAR: 2013 DOI: 10.1007/s11214-012-9926-9 |
|
The Radiation Belt Storm Probes (RBSP)-Energetic Particle, Composition, and Thermal Plasma (ECT) suite contains an innovative complement of particle instruments to ensure the highest quality measurements ever made in the inner magnetosphere and radiation belts. The coordinated RBSP-ECT particle measurements, analyzed in combination with fields and waves observations and state-of-the-art theory and modeling, are necessary for understanding the acceleration, global distribution, and variability of radiation belt electrons and ions, key science objectives of NASA\textquoterights Living With a Star program and the Van Allen Probes mission. The RBSP-ECT suite consists of three highly-coordinated instruments: the Magnetic Electron Ion Spectrometer (MagEIS), the Helium Oxygen Proton Electron (HOPE) sensor, and the Relativistic Electron Proton Telescope (REPT). Collectively they cover, continuously, the full electron and ion spectra from one eV to 10\textquoterights of MeV with sufficient energy resolution, pitch angle coverage and resolution, and with composition measurements in the critical energy range up to 50 keV and also from a few to 50 MeV/nucleon. All three instruments are based on measurement techniques proven in the radiation belts. The instruments use those proven techniques along with innovative new designs, optimized for operation in the most extreme conditions in order to provide unambiguous separation of ions and electrons and clean energy responses even in the presence of extreme penetrating background environments. The design, fabrication and operation of ECT spaceflight instrumentation in the harsh radiation belt environment ensure that particle measurements have the fidelity needed for closure in answering key mission science questions. ECT instrument details are provided in companion papers in this same issue. In this paper, we describe the science objectives of the RBSP-ECT instrument suite on the Van Allen Probe spacecraft within the context of the overall mission objectives, indicate how the characteristics of the instruments satisfy the requirements to achieve these objectives, provide information about science data collection and dissemination, and conclude with a description of some early mission results. Spence, H.; Reeves, G.; Baker, D.; Blake, J.; Bolton, M.; Bourdarie, S.; Chan, A.; Claudpierre, S.; Clemmons, J.; Cravens, J.; Elkington, S.; Fennell, J.; Friedel, R.; Funsten, H.; Goldstein, J.; Green, J.; Guthrie, A.; Henderson, M.; Horne, R.; Hudson, M.; Jahn, J.-M.; Jordanova, V.; Kanekal, S.; Klatt, B.; Larsen, B.; Li, X.; MacDonald, E.; Mann, I.R.; Niehof, J.; O\textquoterightBrien, T.; Onsager, T.; Salvaggio, D.; Skoug, R.; Smith, S.; Suther, L.; Thomsen, M.; Thorne, R.; Published by: Space Science Reviews Published on: 11/2013 YEAR: 2013 DOI: DOI: 10.1007/s11214-013-0007-5 |
| 2006 |
|
The relativistic electron dropout event on 20 November 2003 is studied using data from a number of satellites including SAMPEX, HEO, ACE, POES, and FAST. The observations suggest that the dropout may have been caused by two separate mechanisms that operate at high and low L-shells, respectively, with a separation at L \~ 5. At high L-shells (L > 5), the dropout is approximately independent of energy and consistent with losses to the magnetopause aided by the Dst effect and outward radial diffusion which can deplete relativistic electrons down to lower L-shells. At low L-shells (L < 5), the dropout is strongly energy-dependent, with the higher-energy electrons being affected most. Moreover, large precipitation bands of both relativistic electrons and energetic protons are observed at low L-shells which are consistent with intense pitch angle scattering driven by electromagnetic ion cyclotron (EMIC) waves and may result in a rapid loss of relativistic electrons near the plasmapause in the dusk sector or in plumes of enhanced density. Bortnik, J.; Thorne, R.; O\textquoterightBrien, T.; Green, J.; Strangeway, R.; Shprits, Y; Baker, D.; Published by: Journal of Geophysical Research Published on: 12/2006 YEAR: 2006 DOI: 10.1029/2006JA011802 |
| 2005 |
|
Timescale for MeV electron microburst loss during geomagnetic storms Energetic electrons in the outer radiation belt can resonate with intense bursts of whistler-mode chorus emission leading to microburst precipitation into the atmosphere. The timescale for removal of outer zone MeV electrons during the main phase of the October 1998 magnetic storm has been computed by comparing the rate of microburst loss observed on SAMPEX with trapped flux levels observed on Polar. Effective lifetimes are comparable to a day and are relatively independent of L shell. The lifetimes have also been evaluated by theoretical calculations based on quasi-linear scattering by field-aligned waves. Agreement with the observations requires average wide-band wave amplitudes comparable to 100 pT, which is consistent with the intensity of chorus emissions observed under active conditions. MeV electron scattering is most efficient during first-order cyclotron resonance with chorus emissions at geomagnetic latitudes above 30 degrees. Consequently, the zone of MeV microbursts tends to maximize in the prenoon (0400\textendash1200 MLT) sector, since nightside chorus is more strongly confined to the equator. Thorne, R.; O\textquoterightBrien, T.; Shprits, Y; Summers, D.; Horne, R.; Published by: Journal of Geophysical Research Published on: 09/2005 YEAR: 2005 DOI: 10.1029/2004JA010882 |
| 2004 |
|
Quantification of relativistic electron microburst losses during the GEM storms Bursty precipitation of relativistic electrons has been implicated as a major loss process during magnetic storms. One type of precipitation, microbursts, appears to contain enough electrons to empty the prestorm outer radiation belt in approximately a day. During storms that result in high fluxes of trapped relativistic electrons, microbursts continue for several days into the recovery phase, when trapped fluxes are dramatically increasing. The present study shows that this apparent inconsistency is resolved by observations that the number of electrons lost through microbursts is 10\textendash100 times larger during the main phase than during the recovery phase of several magnetic storms chosen by the Geospace Environment Modeling (GEM) program. O\textquoterightBrien, T.; Looper, M.; Blake, J.; Published by: Geophysical Research Letters Published on: 02/2004 YEAR: 2004 DOI: 10.1029/2003GL018621 |
| 2003 |
|
We examine signatures of two types of waves that may be involved in the acceleration of energetic electrons in Earth\textquoterights outer radiation belts. We have compiled a database of ULF wave power from SAMNET and IMAGE ground magnetometer stations for 1987\textendash2001. Long-duration, comprehensive, in situ VLF/ELF chorus wave observations are not available, so we infer chorus wave activity from low-altitude SAMPEX observations of MeV electron microbursts for 1996\textendash2001 since microbursts are thought to be caused by interactions between chorus and trapped electrons. We compare the ULF and microburst observations to in situ trapped electrons observed by high-altitude satellites from 1989\textendash2001. We find that electron acceleration at low L shells is closely associated with both ULF activity and MeV microbursts and thereby probably also with chorus activity. Electron flux enhancements across the outer radiation belt are, in general, related to both ULF and VLF/ELF activity. However, we suggest that electron flux peaks observed at L \~ 4.5 are likely caused by VLF/ELF wave acceleration, while ULF activity probably produces the dominant electron acceleration at geosynchronous orbit and beyond. O\textquoterightBrien, T.; Lorentzen, K.; Mann, I.; Meredith, N.; Blake, J.; Fennell, J.; Looper, M.; Milling, D.; Anderson, R.; Published by: Journal of Geophysical Research Published on: 08/2003 YEAR: 2003 DOI: 10.1029/2002JA009784 |
1