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

Sandhu, Jasmine, Rae, Jonathan, Freeman, M. P., Gkioulidou, M., Forsyth, C., Reeves, G. D., Murphy, K. R. and Walach, M.‐T. (2019) Substorm‐Ring Current Coupling: A Comparison of Isolated and Compound Substorms. Journal of Geophysical Research: Space Physics, 124 (8). pp. 6776-6791. ISSN 2169-9380

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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 ∼20–30%. Furthermore, we observe a significantly larger magnitude of energization (by ∼40–50%) 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.

Item Type: Article
Uncontrolled Keywords: Funding information: J. K. S. is supported by STFC grant ST/N000722/1 and NERC Grant NE/P017185/1, I. J. R. is supported by STFC Grant ST/N000722/1 and NERC Grant NE/P017185/1, C. F. is supported by NERC IRFNE/N014480/1, K. R. M. is supported by NSF Grant 1602403 and NASA Grants 18‐HGIO18_2‐012 and 18‐HSWO2R18‐0010, and M. ‐T. W. is supported by NERC Grant NE/P001556/1. Processing and analysis of the HOPE data were supported by Energetic Particle, Composition, and Thermal Plasma (RBSP‐ECT) investigation funded under NASAs Prime contract NAS5‐01072. All RBSP‐ECT data are publicly available at the Web site ( The SML index data are publicly available online ( We gratefully acknowledge the SuperMAG collaborators ( The solar wind data and Sym‐H index data are publicly available online (
Subjects: F300 Physics
F500 Astronomy
F800 Physical and Terrestrial Geographical and Environmental Sciences
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: Elena Carlaw
Date Deposited: 01 Apr 2021 08:34
Last Modified: 31 Jul 2021 15:36

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