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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, …
ArXiv.org
Cornell University
04/15/2026
DOI: 10.48550/arxiv.2604.14104
url
https://doi.org/10.48550/arxiv.2604.14104View
Preprint (Author's original) This preprint has not been evaluated by subject experts through peer review. Preprints may undergo extensive changes and/or become peer-reviewed journal articles. Open Access

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 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 minutes 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, i.e., 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.
 Physics - Space Physics

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