The injection region's formation, scale size, and propagation direction have been debated throughout the years, with new questions arising with increased plasma sheet observations by missions like Cluster and THEMIS. How do temporally and spatially small‐scale injections relate to the larger injections historically observed at geosynchronous orbit? How to account for opposing propagation directions—earthward, tailward, and azimuthal—observed by different studies? To address these questions, we used a combination of multisatellite and ground‐based observations to knit together a cohesive story explaining injection formation, propagation, and differing spatial scales and timescales. We used a case study to put statistics into context. First, fast earthward flows with embedded small‐scale dipolarizing flux bundles transport both magnetic flux and energetic particles earthward, resulting in minutes‐long injection signatures. Next, a large‐scale injection propagates azimuthally and poleward/tailward, observed in situ as enhanced flux and on the ground in the riometer signal. The large‐scale dipolarization propagates in a similar direction and speed as the large‐scale electron injection. We suggest small‐scale injections result from earthward‐propagating, small‐scale dipolarizing flux bundles, which rapidly contribute to the large‐scale dipolarization. We suggest the large‐scale dipolarization is the source of the large‐scale electron injection region, such that as dipolarization expands, so does the injection. The >90‐keV ion flux increased and decreased with the plasma flow, which died at the satellites as global dipolarization engulfed them. We suggest the ion injection region at these energies in the plasma sheet is better organized by the plasma flow.
This paper addresses the question of the contribution of azimuthally localized flow channels and magnetic field dipolarizations embedded in them in the global dipolarization of the inner magnetosphere during substorms. We employ the high‐resolution Lyon‐Fedder‐Mobarry global magnetosphere magnetohydrodynamic model and simulate an isolated substorm event, which was observed by the geostationary satellites and by the Magnetospheric Multiscale spacecraft. The results of our simulations reveal that plasma sheet flow channels (bursty bulk flows, BBFs) and elementary dipolarizations (dipolarization fronts, DFs) occur in the growth phase of the substorm but are rare and do not penetrate to the geosynchronous orbit. The substorm onset is characterized by an abrupt increase in the occurrence and intensity of BBFs/DFs, which penetrate well earthward of the geosynchronous orbit during the expansion phase. These azimuthally localized structures are solely responsible for the global (in terms of the magnetic local time) dipolarization of the inner magnetosphere toward the end of the substorm expansion. Comparison with the geostationary satellites and Magnetospheric Multiscale data shows that the properties of the BBFs/DFs in the simulation are similar to those observed, which gives credence to the above results. Additionally, the simulation reveals many previously observed signatures of BBFs and DFs, including overshoots and oscillations around their equilibrium position, strong rebounds and vortical tailward flows, and the corresponding plasma sheet expansion and thinning.more » « less
- NSF-PAR ID:
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Page Range / eLocation ID:
- p. 8647-8668
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The present study investigates dipolarization signatures in the inner magnetosphere using sharp geosynchronous dipolarizations as a reference. The results are summarized as follows: (1) The region of sharp and structured dipolarizations expands earthward while dipolarizations are sustained at geosynchronous orbit; (2) within 5
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The extreme substorm event on 5 April 2010 (
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