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Injection and Transport of the Particle Fluxes During the Substorms That Occurred on 7 September 2017: Multi‐Satellite Observations.

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Title: Injection and Transport of the Particle Fluxes During the Substorms That Occurred on 7 September 2017: Multi‐Satellite Observations.
Authors: Pandya, Megha1,2 (AUTHOR) megha.m.pandya@nasa.gov, Le, Guan1 (AUTHOR), Kang, Suk‐Bin1,2 (AUTHOR), Bhaskar, Ankush3 (AUTHOR), Sibeck, David G.1 (AUTHOR), Reeves, Geoffrey4,5 (AUTHOR), Fok, Mei‐Ching1 (AUTHOR), Rice, Rachel C.1,6 (AUTHOR), Chen, Li‐Jen1 (AUTHOR), Ebihara, Yusuke7 (AUTHOR), Boardsen, Scott A.1,8 (AUTHOR), Ferradas, Cristian P.1,2 (AUTHOR), Kessel, Ramona L.1,2 (AUTHOR), Poh, Gangkai2,9 (AUTHOR), Manweiler, Jerry W.10 (AUTHOR), Henderson, Michael G.4 (AUTHOR)
Source: Journal of Geophysical Research. Space Physics. Feb2026, Vol. 131 Issue 2, p1-19. 19p.
Subject Terms: *Magnetic storms, Magnetosphere, Ion flow dynamics, Magnetic fields, Magnetospheric physics
Company/Entity: Magnetospheric Multiscale Mission (U.S.)
Abstract: We investigate the injection and transport of energetic particles from the Earth's plasma sheet into the inner magnetosphere during the three consecutive substorms that occuurred on 7 September 2017. Using coordinated observations from the MMS, LANL, and Van Allen Probes spacecraft, we track the evolution of ion and electron fluxes from the mid‐tail to the inner magnetosphere. Using the dipole field approximation to trace particle drift orbits from LANL satellites at geosynchronous orbit, we identified the equatorial injection region to extend from ∼2000 to ∼0400 MLT. Subsequently, the injected particles were detected further earthward at Van Allen Probes (L ∼ 4), particularly on the dayside. The multi‐point data reveal that stronger substorms injected ions over a wide energy range (1–200 keV) with significant dayside penetration, while weaker substorms resulted in narrower energy injections (5–30 keV). Back‐tracing the proton drift paths further, calculated using the electric and magnetic fields from the MHD simulation, indicates that convection and adiabatic drifts alone are insufficient to account for the ion injections observed at the Van Allen Probe locations. This suggests that non‐adiabatic processes, such as substorm‐driven impulsive electric fields, are required for particles to reach the same regions. In contrast, electrons at Van Allen Probes lacked clear injection signatures, suggesting the influence of localized electric fields. These results highlight the spatiotemporal complexity of substorm injections and emphasize the value of multi‐point observations and simulations to understand particle transport in the inner magnetosphere. Plain Language Summary: On 7 September 2017, a sequence of substorms allowed us to examine how energetic particles move from the plasma sheet into the inner magnetosphere. Using data from MMS (tail region), LANL (geosynchronous orbit), and the Van Allen Probes (closer to Earth), we tracked ion and electron injections across local time. MMS recorded initial injection signatures including magnetic field changes and fast particles. By calculating the trajectories of protons, we found that the source region extended from ∼20:00 to 04:00 MLT. Injections were observed sequentially at LANL and RBSP, with stronger substorms delivering a wide energy range of ions (1–200 keV), while weaker events were limited to lower energies (5–30 keV). Only intense substorms led to significant ion penetration into the dayside. Interestingly, the electrons exhibit multiple energy‐dependent delays, yet they are difficult to link directly to individual substorms. This suggests that rapid electric‐field variations or localized acceleration processes may influence the electrons, rather than standard gradient‐curvature drift alone. This event highlights the variability of particle transport during substorms and underscores the importance of multi‐point observations in understanding the dynamics of the Earth's magnetosphere. Key Points: Between two substorms, the weaker one causes brief, narrow‐energy proton injections, while stronger yields prolonged, broad enhancementsBetween two substorms, the weaker had a narrow injection region (∼1930–0100 MLT), while the stronger spanned broadly (∼1945–0400) at GEOIon injections arise from combined substorm‐driven impulsive E × B and ∇B drifts—event and location dependent [ABSTRACT FROM AUTHOR]
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Abstract:We investigate the injection and transport of energetic particles from the Earth's plasma sheet into the inner magnetosphere during the three consecutive substorms that occuurred on 7 September 2017. Using coordinated observations from the MMS, LANL, and Van Allen Probes spacecraft, we track the evolution of ion and electron fluxes from the mid‐tail to the inner magnetosphere. Using the dipole field approximation to trace particle drift orbits from LANL satellites at geosynchronous orbit, we identified the equatorial injection region to extend from ∼2000 to ∼0400 MLT. Subsequently, the injected particles were detected further earthward at Van Allen Probes (L ∼ 4), particularly on the dayside. The multi‐point data reveal that stronger substorms injected ions over a wide energy range (1–200 keV) with significant dayside penetration, while weaker substorms resulted in narrower energy injections (5–30 keV). Back‐tracing the proton drift paths further, calculated using the electric and magnetic fields from the MHD simulation, indicates that convection and adiabatic drifts alone are insufficient to account for the ion injections observed at the Van Allen Probe locations. This suggests that non‐adiabatic processes, such as substorm‐driven impulsive electric fields, are required for particles to reach the same regions. In contrast, electrons at Van Allen Probes lacked clear injection signatures, suggesting the influence of localized electric fields. These results highlight the spatiotemporal complexity of substorm injections and emphasize the value of multi‐point observations and simulations to understand particle transport in the inner magnetosphere. Plain Language Summary: On 7 September 2017, a sequence of substorms allowed us to examine how energetic particles move from the plasma sheet into the inner magnetosphere. Using data from MMS (tail region), LANL (geosynchronous orbit), and the Van Allen Probes (closer to Earth), we tracked ion and electron injections across local time. MMS recorded initial injection signatures including magnetic field changes and fast particles. By calculating the trajectories of protons, we found that the source region extended from ∼20:00 to 04:00 MLT. Injections were observed sequentially at LANL and RBSP, with stronger substorms delivering a wide energy range of ions (1–200 keV), while weaker events were limited to lower energies (5–30 keV). Only intense substorms led to significant ion penetration into the dayside. Interestingly, the electrons exhibit multiple energy‐dependent delays, yet they are difficult to link directly to individual substorms. This suggests that rapid electric‐field variations or localized acceleration processes may influence the electrons, rather than standard gradient‐curvature drift alone. This event highlights the variability of particle transport during substorms and underscores the importance of multi‐point observations in understanding the dynamics of the Earth's magnetosphere. Key Points: Between two substorms, the weaker one causes brief, narrow‐energy proton injections, while stronger yields prolonged, broad enhancementsBetween two substorms, the weaker had a narrow injection region (∼1930–0100 MLT), while the stronger spanned broadly (∼1945–0400) at GEOIon injections arise from combined substorm‐driven impulsive E × B and ∇B drifts—event and location dependent [ABSTRACT FROM AUTHOR]
ISSN:21699380
DOI:10.1029/2025JA034513