Persistent Sub-MeV Ion Enhancement Downstream of an Interplanetary Shock: Multispacecraft Observations near L1
11 affiliations
- 1The University of Alabama in Huntsville
- 2Princeton University
- 3Southwest Research Institute
- 4Johns Hopkins University
- 5University of Arizona
- 6Imperial College London
- 7University of Michigan
- 8NASA Goddard Space Flight Center
- 9The Johns Hopkins University
- 10University of New Hampshire
- 11National Oceanographic and Atmospheric Administration NESDIS Office of Space Weather Observations (SWO)
Abstract
On 2026 February 4, an interplanetary shock crossed the L1 region and was followed about 7.7 hr later by a heliospheric current sheet/heliospheric plasma sheet (HCS/HPS), while energetic-ion intensities continued to evolve throughout the intervening downstream region. The shock was observed by IMAP, Wind, ACE, DSCOVR, and SOLAR-1, providing a multispacecraft view of its geometry. Multispacecraft timing and local shock-normal analyses show that the shock is highly quasiperpendicular but spatially nonplanar across L1. Energetic-ion intensities exhibit a pronounced energy-dependent response. Sub-MeV intensities increase well upstream of the shock and remain enhanced throughout the downstream region until approaching the HCS/HPS, whereas intensities above ∼1 MeV show a much weaker downstream enhancement and tend to peak near the shock. The energy spectra also soften downstream, with the fitted spectral break shifting from several MeV near the shock to lower energies farther downstream. Pitch-angle distributions evolve from pronounced field-aligned streaming upstream to enhanced intensities at oblique-to-perpendicular pitch angles downstream, with the anisotropy persisting through much of the downstream sheath and gradually broadening toward the HCS/HPS. A secondary current sheet embedded within the downstream HPS exhibits signatures consistent with a localized reconnection exhaust. Overall, the observations indicate that the sub-MeV ion population is strongly influenced by the shock, while its subsequent downstream evolution is shaped primarily by energy-dependent transport. Localized energization within the disturbed downstream sheath may provide an additional contribution to the sub-MeV population.
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BibTeX
@article{zhao2026persistent,
title = {{Persistent Sub-MeV Ion Enhancement Downstream of an Interplanetary Shock: Multispacecraft Observations near L1}},
author = {L.-L. Zhao and X. Zhu and Y. Jiao and Z. Jin and N. M. Subashchandar and G. P. Zank and A. Silwal and D. J. McComas and M. I. Desai and S. Raptis and J. Giacalone and M. A. Dayeh and M. J. Starkey and K. Ogasawara and S. T. Hart and M. E. Cuesta and L. Y. Khoo and D. Turner and J. S. Rankin and T. S. Horbury and S. A. Livi and E. R. Christian and J. G. Mitchell and M. Gkioulidou and R. B. Torbert and D. Vassiliadis},
journal = {The Astrophysical Journal Supplement Series},
year = {2026},
month = nov,
doi = {10.3847/1538-4365/aeb300},
url = {https://iopscience.iop.org/article/10.3847/1538-4365/aeb300},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Persistent Sub-MeV Ion Enhancement Downstream of an Interplanetary Shock: Multispacecraft Observations near L1
AU - L.-L. Zhao
AU - X. Zhu
AU - Y. Jiao
AU - Z. Jin
AU - N. M. Subashchandar
AU - G. P. Zank
AU - A. Silwal
AU - D. J. McComas
AU - M. I. Desai
AU - S. Raptis
AU - J. Giacalone
AU - M. A. Dayeh
AU - M. J. Starkey
AU - K. Ogasawara
AU - S. T. Hart
AU - M. E. Cuesta
AU - L. Y. Khoo
AU - D. Turner
AU - J. S. Rankin
AU - T. S. Horbury
AU - S. A. Livi
AU - E. R. Christian
AU - J. G. Mitchell
AU - M. Gkioulidou
AU - R. B. Torbert
AU - D. Vassiliadis
PY - 2026
DA - 2026/11/04
JO - The Astrophysical Journal Supplement Series
DO - 10.3847/1538-4365/aeb300
UR - https://iopscience.iop.org/article/10.3847/1538-4365/aeb300
AB - On 2026 February 4, an interplanetary shock crossed the L1 region and was followed about 7.7 hr later by a heliospheric current sheet/heliospheric plasma sheet (HCS/HPS), while energetic-ion intensities continued to evolve throughout the intervening downstream region. The shock was observed by IMAP, Wind, ACE, DSCOVR, and SOLAR-1, providing a multispacecraft view of its geometry. Multispacecraft timing and local shock-normal analyses show that the shock is highly quasiperpendicular but spatially nonplanar across L1. Energetic-ion intensities exhibit a pronounced energy-dependent response. Sub-MeV intensities increase well upstream of the shock and remain enhanced throughout the downstream region until approaching the HCS/HPS, whereas intensities above ∼1 MeV show a much weaker downstream enhancement and tend to peak near the shock. The energy spectra also soften downstream, with the fitted spectral break shifting from several MeV near the shock to lower energies farther downstream. Pitch-angle distributions evolve from pronounced field-aligned streaming upstream to enhanced intensities at oblique-to-perpendicular pitch angles downstream, with the anisotropy persisting through much of the downstream sheath and gradually broadening toward the HCS/HPS. A secondary current sheet embedded within the downstream HPS exhibits signatures consistent with a localized reconnection exhaust. Overall, the observations indicate that the sub-MeV ion population is strongly influenced by the shock, while its subsequent downstream evolution is shaped primarily by energy-dependent transport. Localized energization within the disturbed downstream sheath may provide an additional contribution to the sub-MeV population.
SN - 0067-0049
SN - 1538-4365
ER -