Bibliography

A Revised Look at Relativistic Electrons in the Earth\textquoterights Inner Radiation Zone and Slot Region

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

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

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

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

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.

Selesnick, R.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 10/2015

YEAR: 2015     DOI: 10.1002/2015JA021387

electrons; Inner zone; Radiation belt

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