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Evolution of the Mid‐Latitude Red Aurora Over Northern China During the 5 November 2023 Geomagnetic Storm.

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Title: Evolution of the Mid‐Latitude Red Aurora Over Northern China During the 5 November 2023 Geomagnetic Storm.
Authors: Liang, Jianyun1,2 (AUTHOR), Xu, Jiyao2 (AUTHOR) jyxu@spaceweather.ac.cn, Zhang, Yongliang3 (AUTHOR), Zhang, Shun‐Rong4 (AUTHOR), Wu, Kun5 (AUTHOR), Yuan, Wei2 (AUTHOR), Zhu, Yajun2 (AUTHOR), Li, Guozhu6 (AUTHOR), Liu, Xiao2,7 (AUTHOR)
Source: Journal of Geophysical Research. Space Physics. Oct2025, Vol. 130 Issue 10, p1-14. 14p.
Subject Terms: *Magnetic storms, Auroras, Electron temperature, Ionospheric disturbances, Ion emission
Geographic Terms: China
Abstract: This study presents novel observations of a mid‐latitude red aurora event at 44°MLAT over Northern China during the 5 November 2023 geomagnetic storm, using simultaneous observations from ground‐based instruments (630 nm all‐sky imager (ASI) and ionosonde) at Mohe station (53.5°N, 122.4°E; MLAT = 44.32°N) and space‐based satellites (Swarm and Defense Meteorological Satellite Program F17 and F18). The auroras displayed unusual dynamics, appearing north of the ASI field of view (FOV) at 1000 UT, disappearing at 1300 UT, then reappearing at 1400 UT with equatorward expansion (∼62 m/s) to reach 51°N (42°MLAT/2.3 L) and lasting ∼8 hr. Analysis indicated that the auroral characteristics resembled stable auroral red arc (SARc), including thermal excitation (electron temperatures >3,000 K) and ionogram features (weak spread‐F occurrence and reduced critical frequency). The auroras exhibited distinctive yet previously unreported properties of SARc, prompting their definition as SARc‐like events. Specifically, the auroral emissions demonstrated clear additional contributions from ion precipitation (hundreds eV to tens keV ions) alongside thermal excitation of the typical SAR theory, and they were not fixed within the ionospheric trough unlike a narrow band of typical SARc pattern. The ionospheric trough at its equatorward edge exhibited synchronous equatorward motion. Concurrently, ionosonde echoes weakened and disappeared as the aurora and trough passed overhead, suggesting density depletion effects. Both the trough dynamics and ion precipitation likely drove electron temperature enhancements. These findings reveal new complexities in mid‐latitude auroral physics requiring further investigation. Plain Language Summary: The colorful auroras in polar regions are attributed to the interaction of solar winds with the Earth's magnetosphere. Mid‐latitude auroras only appear during severe geomagnetic storms or substorms and primarily enhance 630 nm [OI] emission. In this study, we report multiple instrument observations of the mid‐latitude red auroras on 5 November 2023, which lasted for approximately 11 hr. The aurora first appeared north of the ASI's FOV at Mohe station at 1000 UT, lasted for ∼3 hr, and then disappeared. It reappeared at 1400 UT, expanded equatorward between 1500 and 1800 UT, and remained in the ASI's FOV until sunrise. Simultaneous satellite and ground observations showed that the red aurora exhibited partly SARc signatures (high temperature, spread‐F occurrence, and reduced critical frequency) and previously unreported features (significant ion precipitation in emission region and north‐south extension unconfined inside the ionospheric trough), defining them as SAR‐like events. The ionospheric trough was positioned at its equatorward edge. Furthermore, ionosonde echoes showed weakening and even disappearing during the auroral and trough passage likely due to the density depletion effect. Moreover, electron temperature enhancement in the auroral region was closely linked to ion precipitation and low density in the trough. Key Points: The first report of mid‐latitude red aurora at 44°MLAT over Northern China was provided by multiple data during 5 November 2023 stormAnalysis revealed that the mid‐latitude red aurora was stable auroral red arc (SARc)‐like aurora, but its emission was additionally involved in ion precipitationIonospheric trough coincided with SARc‐like aurora motion (63 m/s equatorward) and weakening ionosonde echoes as it passed overhead station [ABSTRACT FROM AUTHOR]
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Abstract:This study presents novel observations of a mid‐latitude red aurora event at 44°MLAT over Northern China during the 5 November 2023 geomagnetic storm, using simultaneous observations from ground‐based instruments (630 nm all‐sky imager (ASI) and ionosonde) at Mohe station (53.5°N, 122.4°E; MLAT = 44.32°N) and space‐based satellites (Swarm and Defense Meteorological Satellite Program F17 and F18). The auroras displayed unusual dynamics, appearing north of the ASI field of view (FOV) at 1000 UT, disappearing at 1300 UT, then reappearing at 1400 UT with equatorward expansion (∼62 m/s) to reach 51°N (42°MLAT/2.3 L) and lasting ∼8 hr. Analysis indicated that the auroral characteristics resembled stable auroral red arc (SARc), including thermal excitation (electron temperatures >3,000 K) and ionogram features (weak spread‐F occurrence and reduced critical frequency). The auroras exhibited distinctive yet previously unreported properties of SARc, prompting their definition as SARc‐like events. Specifically, the auroral emissions demonstrated clear additional contributions from ion precipitation (hundreds eV to tens keV ions) alongside thermal excitation of the typical SAR theory, and they were not fixed within the ionospheric trough unlike a narrow band of typical SARc pattern. The ionospheric trough at its equatorward edge exhibited synchronous equatorward motion. Concurrently, ionosonde echoes weakened and disappeared as the aurora and trough passed overhead, suggesting density depletion effects. Both the trough dynamics and ion precipitation likely drove electron temperature enhancements. These findings reveal new complexities in mid‐latitude auroral physics requiring further investigation. Plain Language Summary: The colorful auroras in polar regions are attributed to the interaction of solar winds with the Earth's magnetosphere. Mid‐latitude auroras only appear during severe geomagnetic storms or substorms and primarily enhance 630 nm [OI] emission. In this study, we report multiple instrument observations of the mid‐latitude red auroras on 5 November 2023, which lasted for approximately 11 hr. The aurora first appeared north of the ASI's FOV at Mohe station at 1000 UT, lasted for ∼3 hr, and then disappeared. It reappeared at 1400 UT, expanded equatorward between 1500 and 1800 UT, and remained in the ASI's FOV until sunrise. Simultaneous satellite and ground observations showed that the red aurora exhibited partly SARc signatures (high temperature, spread‐F occurrence, and reduced critical frequency) and previously unreported features (significant ion precipitation in emission region and north‐south extension unconfined inside the ionospheric trough), defining them as SAR‐like events. The ionospheric trough was positioned at its equatorward edge. Furthermore, ionosonde echoes showed weakening and even disappearing during the auroral and trough passage likely due to the density depletion effect. Moreover, electron temperature enhancement in the auroral region was closely linked to ion precipitation and low density in the trough. Key Points: The first report of mid‐latitude red aurora at 44°MLAT over Northern China was provided by multiple data during 5 November 2023 stormAnalysis revealed that the mid‐latitude red aurora was stable auroral red arc (SARc)‐like aurora, but its emission was additionally involved in ion precipitationIonospheric trough coincided with SARc‐like aurora motion (63 m/s equatorward) and weakening ionosonde echoes as it passed overhead station [ABSTRACT FROM AUTHOR]
ISSN:21699380
DOI:10.1029/2024JA032729