Bibliography

Substorm-Ring Current Coupling: A Comparison of Isolated and Compound Substorms

Substorms are a highly variable process, which can occur as an isolated event or as part of a sequence of multiple substorms (compound substorms). In this study we identify how the low-energy population of the ring current and subsequent energization varies for isolated substorms compared to the first substorm of a compound event. Using observations of H+ and O+ ions (1 eV to 50 keV) from the Helium Oxygen Proton Electron instrument onboard Van Allen Probe A, we determine the energy content of the ring current in L-MLT space. We observe that the ring current energy content is significantly enhanced during compound substorms as compared to isolated substorms by \~20\textendash30\%. Furthermore, we observe a significantly larger magnitude of energization (by \~40\textendash50\%) following the onset of compound substorms relative to isolated substorms. Analysis suggests that the differences predominantly arise due to a sustained enhancement in dayside driving associated with compound substorms compared to isolated substorms. The strong solar wind driving prior to onset results in important differences in the time history of the magnetosphere, generating significantly different ring current conditions and responses to substorms. The observations reveal information about the substorm injected population and the transport of the plasma in the inner magnetosphere.

Sandhu, J.; Rae, I.; Freeman, M.; Gkioulidou, M.; Forsyth, C.; Reeves, G.; Murphy, K.; Walach, M.-T.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 08/2019

YEAR: 2019     DOI: 10.1029/2019JA026766

inner magnetosphere; ring current; substorms; Van Allen; Van Allen Probes

Energisation of the ring current by substorms

The substorm process releases large amounts of energy into the magnetospheric system, although where the energy is transferred to and how it is partitioned remains an open question. In this study, we address whether the substorm process contributes a significant amount of energy to the ring current. The ring current is a highly variable region, and understanding the energisation processes provides valuable insight into how substorm - ring current coupling may contribute to the generation of storm conditions and provide a source of energy for wave driving. In order to quantify the energy input into the ring current during the substorm process, we analyse RBSPICE and HOPE ion flux measurements for H+, O+, and He+. The energy content of the ring current is estimated and binned spatially for L and MLT. The results are combined with an independently derived substorm event list to perform a statistical analysis of variations in the ring current energy content with substorm phase. We show that the ring current energy is significantly higher in the expansion phase compared to the growth phase, with the energy enhancement persisting into the substorm recovery phase. The characteristics of the energy enhancement suggest the injection of energised ions from the tail plasma sheet following substorm onset. The local time variations indicate a loss of energetic H+ ions in the afternoon sector, likely due to wave-particle interactions. Overall, we find that the average energy input into the ring current is \~9\% of the previously reported energy released during substorms.

Sandhu, J.; Rae, I.; Freeman, M.; Forsyth, C.; Gkioulidou, M.; Reeves, G.; Spence, H.; Jackman, C.; Lam, M.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 09/2018

YEAR: 2018     DOI: 10.1029/2018JA025766

BSPICE; HOPE; Magnetosphere; ring current; substorms; Van Allen Probes

What effect do substorms have on the content of the radiation belts?

Substorms are fundamental and dynamic processes in the magnetosphere, converting captured solar wind magnetic energy into plasma energy. These substorms have been suggested to be a key driver of energetic electron enhancements in the outer radiation belts. Substorms inject a keV \textquotedblleftseed\textquotedblright population into the inner magnetosphere which is subsequently energized through wave-particle interactions up to relativistic energies; however, the extent to which substorms enhance the radiation belts, either directly or indirectly, has never before been quantified. In this study, we examine increases and decreases in the total radiation belt electron content (TRBEC) following substorms and geomagnetically quiet intervals. Our results show that the radiation belts are inherently lossy, shown by a negative median change in TRBEC at all intervals following substorms and quiet intervals. However, there are up to 3 times as many increases in TRBEC following substorm intervals. There is a lag of 1\textendash3 days between the substorm or quiet intervals and their greatest effect on radiation belt content, shown in the difference between the occurrence of increases and losses in TRBEC following substorms and quiet intervals, the mean change in TRBEC following substorms or quiet intervals, and the cross correlation between SuperMAG AL (SML) and TRBEC. However, there is a statistically significant effect on the occurrence of increases and decreases in TRBEC up to a lag of 6 days. Increases in radiation belt content show a significant correlation with SML and SYM-H, but decreases in the radiation belt show no apparent link with magnetospheric activity levels.

Forsyth, C.; Rae, I.; Murphy, K.; Freeman, M.; Huang, C.-L.; Spence, H.; Boyd, A.; Coxon, J.; Jackman, C.; Kalmoni, N.; Watt, C.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 06/2016

YEAR: 2016     DOI: 10.1002/2016JA022620

enhancements; losses; Radiation belts; substorm

Helium, Oxygen, Proton, and Electron (HOPE) Mass Spectrometer for the Radiation Belt Storm Probes Mission

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

RBSP; Van Allen Probes