Electron Dispersion at the Electron Edge of the Earth's Magnetospheric Cusp

J. S. Halekas; S. A. Henderson; S. R. Bounds; S. Ruhunusiri; A Moore; I. W. Christopher; D. M. Miles; J. B. Bonnell; B. L. Burkholder; I. H. Cairns; L.‐J. Chen; H. K. Connor; I. M. DesJardin; J. C. Dorelli; C. Feltman; S. A. Fuselier; K. Goodrich; G. Hospodarsky; A. N. Jaynes; J. Labelle; M. Øieroset; S. M. Petrinec; B. Powers; K. J. Trattner; S. L. Soni; R. Strangeway; D. Sur

doi:10.1029/2026GL122699

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Electron Dispersion at the Electron Edge of the Earth's Magnetospheric Cusp

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Electron Dispersion at the Electron Edge of the Earth's Magnetospheric Cusp

J. S. Halekas, S. A. Henderson, S. R. Bounds, S. Ruhunusiri, A Moore, I. W. Christopher, D. M. Miles, J. B. Bonnell, B. L. Burkholder, I. H. Cairns, …

Geophysical research letters, Vol.53(10), e2026GL122699

05/28/2026

DOI: 10.1029/2026GL122699

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Abstract

The Tandem Reconnection and Cusp Electrodynamics Reconnaissance Satellites (TRACERS) mission observes electron energy‐latitude dispersion at the equatorward edge of the magnetospheric cusp, and high‐cadence Analyzer for Cusp Electrons (ACE) measurements resolve the dispersed edge. The inverse velocity dispersion (low energy before high energy) encountered by TRACERS as it travels southward through the northern cusp rules out pure energy‐time dispersion from nearby injections or Alfvén wave‐driven acceleration. TRACERS observes electron dispersion at the equatorward edge of the northern cusp roughly half of the time for southward interplanetary magnetic field (IMF), and almost never for northward IMF. The TRACERS measurements therefore provide strong observational support for the hypothesis that the observed electron dispersion results from dayside magnetic reconnection and plasma convection, much like the ion dispersion that commonly extends across the cusp. Observations of multiple electron dispersions and electron steps suggest fine‐scale spatial and/or temporal variability in magnetic reconnection. The global magnetic field of the Earth represents a barrier to charged particles from the solar wind. The process of magnetic reconnection can open a pathway through this barrier, allowing particles of solar origin to access the polar regions in the funnel‐shaped cusp region. The combination of particle motion along the magnetic field and global convection of plasma through the magnetosphere leads to spatial dispersion, with faster particles accessing the polar regions at different locations from slower particles. This dispersion represents a well‐known phenomenon for ions in the cusp. Similar effects can also occur for electrons, but the high speed of the lighter electrons ensures that dispersion is confined to a very narrow layer at the edge of the cusp. The Tandem Reconnection and Cusp Electrodynamics Reconnaissance Satellites (TRACERS) mission, with an orbit tailored to encounter the cusp and high‐cadence particle measurements, enables the first comprehensive studies of cusp electron dispersion. TRACERS regularly observes and resolves electron energy‐latitude dispersion at the equatorward edge of the magnetospheric cusp The dispersion in the northern cusp is inconsistent with pure energy‐time dispersion, suggesting that plasma convection plays a role Dispersion occurs preferentially for southward interplanetary magnetic field, consistent with an origin related to magnetic reconnection

terrestrial magnetosphere

cusp

reconnection

electron dispersion

TRACERS

UIOWA OA Agreement

Details

Title: Subtitle: Electron Dispersion at the Electron Edge of the Earth's Magnetospheric Cusp
Creators: J. S. Halekas - University of Iowa
S. A. Henderson - University of Iowa
S. R. Bounds - University of Iowa
S. Ruhunusiri - Laboratory for Atmospheric and Space Physics
A Moore - University of Iowa
I. W. Christopher - University of Iowa
D. M. Miles - University of Iowa
J. B. Bonnell - University of California, Berkeley
B. L. Burkholder - Goddard Space Flight Center
I. H. Cairns - The University of Sydney
L.‐J. Chen - Goddard Space Flight Center
H. K. Connor - Goddard Space Flight Center
I. M. DesJardin - Goddard Space Flight Center
J. C. Dorelli - Goddard Space Flight Center
C. Feltman - University of Iowa
S. A. Fuselier - Southwest Research Institute
K. Goodrich - West Virginia University
G. Hospodarsky - University of Iowa
A. N. Jaynes - University of Iowa
J. Labelle - Dartmouth College
M. Øieroset - University of California, Berkeley
S. M. Petrinec - Lockheed Martin (United States)
B. Powers - University of Iowa
K. J. Trattner - University of Colorado Boulder
S. L. Soni - University of Iowa
R. Strangeway - University of California, Los Angeles
D. Sur - Goddard Space Flight Center
Resource Type: Journal article
Publication Details: Geophysical research letters, Vol.53(10), e2026GL122699
DOI: 10.1029/2026GL122699
ISSN: 0094-8276
eISSN: 1944-8007
Publisher: Wiley
Grant note: National Aeronautics and Space Administration: 80GSFC18C0008
We acknowledge the tremendous efforts of the TRACERS engineering and management team across all of its partner institutions in successfully developing, launching, and commissioning the TRACERS spacecraft and their scientific instruments. The TRACERS mission is supported by NASA through contract 80GSFC18C0008.
Language: English
Date published: 05/28/2026
Academic Unit: Physics and Astronomy; University College Courses
Record Identifier: 9985164610102771

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