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Observation of O+ Characteristics During the Terrestrial Alfvén Wing State Induced by the April 2023 Coronal Mass Ejection.

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Title: Observation of O+ Characteristics During the Terrestrial Alfvén Wing State Induced by the April 2023 Coronal Mass Ejection.
Authors: Liang, Haoming1,2 (AUTHOR) haoming@umd.edu, Chen, Li‐Jen2 (AUTHOR), Fuselier, Stephen A.3,4 (AUTHOR), Gomez, Roman G.3 (AUTHOR), Burkholder, Brandon2,5 (AUTHOR), Bessho, Naoki1,2 (AUTHOR), Gurram, Harsha1,2 (AUTHOR), Rice, Rachel C.1,2 (AUTHOR), Shuster, Jason6 (AUTHOR), Ardakani, Akhtar S.6 (AUTHOR)
Source: Journal of Geophysical Research. Space Physics. Apr2025, Vol. 130 Issue 4, p1-10. 10p.
Subject Terms: *Geomagnetism, Solar wind, Ion traps, Magnetic ions, Heavy ions, Coronal mass ejections
Abstract: We report Magnetospheric Multiscale observations of oxygen ions (O+) during a coronal mass ejection (CME) in April 2023 when the solar wind was sub‐Alfvénic and Alfvén wings formed. For the first time, O+ characteristics are studied at the contact region between the unshocked solar wind and the magnetosphere. The O+ ions show energies between 100s eV and ∼30 keV. The possible sources are the ring current, the warm plasma cloak, and the ionosphere. The O+ ions exhibit bi‐directional streaming along newly‐formed closed field lines (CFLs), and dominantly anti‐parallel on earlier‐formed CFLs. Escaping O+ ions in the unshocked solar wind are observed. During the recovery phase, the O+ pitch‐angle distribution associated with flux tubes shows dispersion, indicating potential loss to the solar wind. Our results show escaping as well as trapped O+ ions in the region where a magnetic cloud, an Alfvén wing, and magnetospheric field lines are mixed. Plain Language Summary: During a coronal mass ejection in April 2023, NASA's Magnetospheric Multiscale mission observed oxygen ions (O+) under a rare sub‐Alfvénic solar wind condition, which turned Earth's magnetic field into special magnetic structures called Alfvén wings. This study is the first to look at O+ ions in the area where the unshocked solar wind meets Earth's magnetosphere during Alfvén wing state. The O+ ions had energies from a few hundred electron volts (eV) to about 30,000 eV. These O+ ions likely came from different regions around Earth, including the ring current, the warm plasma cloak, and the ionosphere. The O+ ions moved in both directions along newly‐formed closed magnetic field lines and mainly in one direction along field lines that formed earlier. Some O+ ions were observed in the solar wind, showing a dispersion pattern that suggests they might be lost to space during the recovery phase of the Alfvén wing state. Overall, the study found both escaping and trapped O+ ions in the area where the field lines of the solar wind, the Alfvén wings, and Earth's magnetosphere mix. This helps us understand how the O+ ions behave during Alfvén wing states and their potential loss to space. Key Points: O+ ions showed field‐aligned bidirectional streaming on newly‐formed closed field lines (CFLs) and dominant antiparallel flux on earlier‐formed CFLsO+ ions along with energetic protons and electrons escaped from the magnetosphere into the unshocked solar windThe antiparallel O+ flux reduction was associated with flux tube encounters, indicating potential loss during Alfvén wing recovery [ABSTRACT FROM AUTHOR]
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Abstract:We report Magnetospheric Multiscale observations of oxygen ions (O+) during a coronal mass ejection (CME) in April 2023 when the solar wind was sub‐Alfvénic and Alfvén wings formed. For the first time, O+ characteristics are studied at the contact region between the unshocked solar wind and the magnetosphere. The O+ ions show energies between 100s eV and ∼30 keV. The possible sources are the ring current, the warm plasma cloak, and the ionosphere. The O+ ions exhibit bi‐directional streaming along newly‐formed closed field lines (CFLs), and dominantly anti‐parallel on earlier‐formed CFLs. Escaping O+ ions in the unshocked solar wind are observed. During the recovery phase, the O+ pitch‐angle distribution associated with flux tubes shows dispersion, indicating potential loss to the solar wind. Our results show escaping as well as trapped O+ ions in the region where a magnetic cloud, an Alfvén wing, and magnetospheric field lines are mixed. Plain Language Summary: During a coronal mass ejection in April 2023, NASA's Magnetospheric Multiscale mission observed oxygen ions (O+) under a rare sub‐Alfvénic solar wind condition, which turned Earth's magnetic field into special magnetic structures called Alfvén wings. This study is the first to look at O+ ions in the area where the unshocked solar wind meets Earth's magnetosphere during Alfvén wing state. The O+ ions had energies from a few hundred electron volts (eV) to about 30,000 eV. These O+ ions likely came from different regions around Earth, including the ring current, the warm plasma cloak, and the ionosphere. The O+ ions moved in both directions along newly‐formed closed magnetic field lines and mainly in one direction along field lines that formed earlier. Some O+ ions were observed in the solar wind, showing a dispersion pattern that suggests they might be lost to space during the recovery phase of the Alfvén wing state. Overall, the study found both escaping and trapped O+ ions in the area where the field lines of the solar wind, the Alfvén wings, and Earth's magnetosphere mix. This helps us understand how the O+ ions behave during Alfvén wing states and their potential loss to space. Key Points: O+ ions showed field‐aligned bidirectional streaming on newly‐formed closed field lines (CFLs) and dominant antiparallel flux on earlier‐formed CFLsO+ ions along with energetic protons and electrons escaped from the magnetosphere into the unshocked solar windThe antiparallel O+ flux reduction was associated with flux tube encounters, indicating potential loss during Alfvén wing recovery [ABSTRACT FROM AUTHOR]
ISSN:21699380
DOI:10.1029/2025JA033915