Simultaneous TRACERS and THEMIS Observations of Reversed Cusp Ion Dispersions and Dual‐Lobe Reconnection

M Øieroset; S. A Fuselier; J. B Bonnell; R. A Roglans; J. S Halekas; R. J Strangeway; T. D Phan; R. G Gomez; S. M Petrinec; K. J Trattner; S. R Shaver; K. A Goodrich; S. A Henderson; S. L Soni; V Angelopoulos; B. L Burkholder; H Cao; L.‐J Chen; H. K Connor; D. M Miles; A Moore; J Ng; Y Shen

doi:10.1029/2026GL123404

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Simultaneous TRACERS and THEMIS Observations of Reversed Cusp Ion Dispersions and Dual‐Lobe Reconnection

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Simultaneous TRACERS and THEMIS Observations of Reversed Cusp Ion Dispersions and Dual‐Lobe Reconnection

M Øieroset, S. A Fuselier, J. B Bonnell, R. A Roglans, J. S Halekas, R. J Strangeway, T. D Phan, R. G Gomez, S. M Petrinec, K. J Trattner, …

Geophysical research letters, Vol.53(13), e2026GL123404

07/16/2026

DOI: 10.1029/2026GL123404

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Abstract

We present observations from two consecutive TRACERS‐2 orbits through the northern low‐altitude cusp. During the first crossing, TRACERS‐2 observed reversed cusp ion dispersion and sunward convection, consistent with magnetopause reconnection tailward of the cusp during this northward IMF interval. Simultaneous THEMIS‐D observations at the equatorial magnetopause show heated magnetosheath plasma captured on closed field lines, with similar particle spectra as in the low‐altitude cusp, indicating that reconnection indeed occurred tailward of the cusp and in both hemispheres. When TRACERS‐2 traversed the northern cusp again, 95 min later, the IMF was dominated by a negative BX component. Despite the different IMF conditions, TRACERS‐2 recorded nearly the same cusp signatures as before, that is, reversed ion dispersion and sunward convection. The observations indicate that tailward‐of‐cusp reconnection can occur for both northward and BX‐dominated IMF and that these distinct IMF geometries can produce remarkably similar plasma and field signatures in the low‐altitude cusp.

Hemispheres

Altitude

Convection

Cusps

Dispersion

Dispersions

Electric fields

Line spectra

Magnetic fields

Magnetopause

Magnetopause reconnection

Magnetosheath

Satellites

Spacecraft

Tracers

Details

Title: Subtitle: Simultaneous TRACERS and THEMIS Observations of Reversed Cusp Ion Dispersions and Dual‐Lobe Reconnection
Creators: M Øieroset - University of California, Berkeley
S. A Fuselier - Southwest Research Institute
J. B Bonnell
R. A Roglans - University of California, Berkeley
J. S Halekas - University of Iowa
R. J Strangeway - University of California, Los Angeles
T. D Phan - University of California, Berkeley
R. G Gomez - Southwest Research Institute
S. M Petrinec - Lockheed Martin (United States)
K. J Trattner - University of Colorado Boulder
S. R Shaver - West Virginia University
K. A Goodrich - West Virginia University
S. A Henderson - University of Iowa
S. L Soni - University of Iowa
V Angelopoulos - University of California, Los Angeles
B. L Burkholder - Heliophysics
H Cao - University of California, Los Angeles
L.‐J Chen
H. K Connor - Goddard Space Flight Center
D. M Miles - University of Iowa
A Moore - University of Iowa
J Ng - University of Maryland, College Park
Y Shen - University of Alberta
Resource Type: Journal article
Publication Details: Geophysical research letters, Vol.53(13), e2026GL123404
DOI: 10.1029/2026GL123404
ISSN: 0094-8276
eISSN: 1944-8007
Publisher: John Wiley & Sons, Inc
Grant note: NSF: PHY-2409449 NASA: 80GSFC18C0008, NAS5-02099, 80NSSC20K1781
This research was supported by NASA contracts 80GSFC18C0008 and NAS5-02099, and by NSF Grant PHY-2409449 and NASA LWS Grant 80NSSC20K1781 at UC Berkeley.
Language: English
Date published: 07/16/2026
Academic Unit: Physics and Astronomy
Record Identifier: 9985179240602771

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