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Solar Wind‐Magnetosphere‐Ionosphere Coupling During the October 2024 Storms.

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Title: Solar Wind‐Magnetosphere‐Ionosphere Coupling During the October 2024 Storms.
Authors: Milan, S. E.1 (AUTHOR) steve.milan@le.ac.uk, Mooney, M. K.1 (AUTHOR), Bower, G. E.1 (AUTHOR), Hodnett, R. M.1 (AUTHOR), Amerstorfer, U. V.2 (AUTHOR), Möstl, C.2 (AUTHOR), Samsonov, A.3 (AUTHOR), Anderson, B. J.4 (AUTHOR), Gjerloev, J.5 (AUTHOR), Vines, S. K.6 (AUTHOR)
Source: Journal of Geophysical Research. Space Physics. May2026, Vol. 131 Issue 5, p1-18. 18p.
Subject Terms: *Magnetic storms, *Ionosphere, Magnetosphere, Coronal mass ejections, Magnetospheric physics, Electric currents, Solar wind
Abstract: Two geomagnetic storms occurred in October 2024 (Oct 6‐9 and 10–12), driven by the impact of a series of interplanetary coronal mass ejections on the magnetosphere. The first was a moderate storm, with peak Sym‐H near −150 nT, whereas the second was intense, Sym‐H reaching −340 nT. We compare and contrast the magnetospheric dynamics in each case, using observations of field‐aligned currents (FACs) from the Active Magnetospheric and Planetary Electrodynamics Response Experiment (AMPERE) and ground magnetic perturbations observed by SuperMAG. The first storm responded linearly to solar wind driving, quantified by a dayside reconnection coupling function, and displayed typical substorm dynamics. The response during the second storm suggests that the cross‐polar cap potential saturated, and that the dynamics of the inner magnetosphere were complicated. Magnetospheric compression by high solar wind pressure during the passage of the sheath of the second storm produced elevated FAC magnitudes, indicating that both convection and compression control magnetosphere‐ionosphere coupling. We introduce a new FAC pattern complexity index which shows quantitively that the FAC pattern during the first storm largely retained the region 1 and 2 configuration associated with twin‐cell ionospheric convection, but that during the second storm the pattern became more highly structured. We conclude that storm intensity should not solely be quantified by Sym‐H but also by other aspects of the magnetospheric response to solar wind disturbances. Plain Language Summary: Geomagnetic storms are periods when vivid auroral displays entertain us, but also when activity within the magnetosphere can be hazardous for technological systems including satellites, telecoms networks, and power grids. The intensity of storms is traditionally quantified by the ring current index Sym‐H, which measures magnetic perturbations produced by the Earth's ring current. We study the magnetospheric dynamics during two storms that occurred during October 2024, and show that qualitatively and quantitatively the response was different in both cases. We identify that one responded linearly to conditions within the solar wind, whereas the other displayed a more complicated, non‐linear response that included a reaction to the pressure of the solar wind. We conclude that the intensity of a storm should be judged by its multifaceted dynamics rather than just a sole index such as Sym‐H. Key Points: Two geomagnetic storms during October 2024 display different responses to solar wind drivingField‐aligned current magnitudes show linear and saturated responses to moderate and intense drivingBoth dayside reconnection rate and magnetospheric compression modulate FAC magnitude and geomagnetic activity [ABSTRACT FROM AUTHOR]
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Abstract:Two geomagnetic storms occurred in October 2024 (Oct 6‐9 and 10–12), driven by the impact of a series of interplanetary coronal mass ejections on the magnetosphere. The first was a moderate storm, with peak Sym‐H near −150 nT, whereas the second was intense, Sym‐H reaching −340 nT. We compare and contrast the magnetospheric dynamics in each case, using observations of field‐aligned currents (FACs) from the Active Magnetospheric and Planetary Electrodynamics Response Experiment (AMPERE) and ground magnetic perturbations observed by SuperMAG. The first storm responded linearly to solar wind driving, quantified by a dayside reconnection coupling function, and displayed typical substorm dynamics. The response during the second storm suggests that the cross‐polar cap potential saturated, and that the dynamics of the inner magnetosphere were complicated. Magnetospheric compression by high solar wind pressure during the passage of the sheath of the second storm produced elevated FAC magnitudes, indicating that both convection and compression control magnetosphere‐ionosphere coupling. We introduce a new FAC pattern complexity index which shows quantitively that the FAC pattern during the first storm largely retained the region 1 and 2 configuration associated with twin‐cell ionospheric convection, but that during the second storm the pattern became more highly structured. We conclude that storm intensity should not solely be quantified by Sym‐H but also by other aspects of the magnetospheric response to solar wind disturbances. Plain Language Summary: Geomagnetic storms are periods when vivid auroral displays entertain us, but also when activity within the magnetosphere can be hazardous for technological systems including satellites, telecoms networks, and power grids. The intensity of storms is traditionally quantified by the ring current index Sym‐H, which measures magnetic perturbations produced by the Earth's ring current. We study the magnetospheric dynamics during two storms that occurred during October 2024, and show that qualitatively and quantitatively the response was different in both cases. We identify that one responded linearly to conditions within the solar wind, whereas the other displayed a more complicated, non‐linear response that included a reaction to the pressure of the solar wind. We conclude that the intensity of a storm should be judged by its multifaceted dynamics rather than just a sole index such as Sym‐H. Key Points: Two geomagnetic storms during October 2024 display different responses to solar wind drivingField‐aligned current magnitudes show linear and saturated responses to moderate and intense drivingBoth dayside reconnection rate and magnetospheric compression modulate FAC magnitude and geomagnetic activity [ABSTRACT FROM AUTHOR]
ISSN:21699380
DOI:10.1029/2026JA035225