Radio emissions reveal Alfvénic activity and electron acceleration prior to substorm onset

Magnetospheric substorms are among the most dynamic phenomena in the Earth's magnetosphere, yet their triggering mechanisms remain unclear. Ground-based observations have identified wave-like aurora as precursors to substorms. Here, we report a new precursor feature in space-based observations of auroral kilometric radiation (AKR), marked by the appearance of emissions with slowly frequency-drifting tones (<2 kHz/s) above 100 kHz. Simultaneous multi-instrument observations and statistical analysis suggest that these AKR precursors occur concurrently with wave-like aurora, either manifesting as pseudo-breakup features (with about 5 min duration) or as pre-onset activity (about 2 min prior to substorm expansion), indicating a common driving mechanism. Analysis of the emissions with frequency-drifting tones suggests that they are linked to moving double layers driven by dispersive Alfvén waves, consistent with an Alfvénic acceleration mechanism for pre-onset aurora. These findings highlight the importance of Alfvénic activity in substorms and suggest that Alfvénic acceleration is not only responsible for optical auroral features but also for radio emissions, potentially explaining also the ubiquitous frequency-drifting emission features observed at other magnetized planets like Saturn and Jupiter.

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Publication Details

Journal
Nature Communications
Published
2025-11-26
DOI
https://doi.org/10.1038/s41467-025-65580-8
Primary Topic
Ionosphere and magnetosphere dynamics
Type
article
Field-Weighted Citation Impact
0.00
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article

Radio emissions reveal Alfvénic activity and electron acceleration prior to substorm onset

Laurent Lamy, Yasumasa Kasaba, Shengyi Ye, S. B. Mende et al.
Nature Communications
Ionosphere and magnetosphere dynamics
article

Radio emissions reveal Alfvénic activity and electron acceleration prior to substorm onset

Laurent Lamy, Yasumasa Kasaba, Shengyi Ye, S. B. Mende, Fuminori Tsuchiya, A. R. Fogg, Satoshi Kurita, L. J. Paxton, Siyuan Wu, C. M. Jackman, P. Zarka, Daniel Whiter, Nawapat Kaweeyanun, James Waters, Hirotsugu Kojima, Yoshizumi Miyoshi, Mengmeng Wang, Atsuki Shinbori, Y. Kasahara
article en

Abstract

Magnetospheric substorms are among the most dynamic phenomena in the Earth's magnetosphere, yet their triggering mechanisms remain unclear. Ground-based observations have identified wave-like aurora as precursors to substorms. Here, we report a new precursor feature in space-based observations of auroral kilometric radiation (AKR), marked by the appearance of emissions with slowly frequency-drifting tones (<2 kHz/s) above 100 kHz. Simultaneous multi-instrument observations and statistical analysis suggest that these AKR precursors occur concurrently with wave-like aurora, either manifesting as pseudo-breakup features (with about 5 min duration) or as pre-onset activity (about 2 min prior to substorm expansion), indicating a common driving mechanism. Analysis of the emissions with frequency-drifting tones suggests that they are linked to moving double layers driven by dispersive Alfvén waves, consistent with an Alfvénic acceleration mechanism for pre-onset aurora. These findings highlight the importance of Alfvénic activity in substorms and suggest that Alfvénic acceleration is not only responsible for optical auroral features but also for radio emissions, potentially explaining also the ubiquitous frequency-drifting emission features observed at other magnetized planets like Saturn and Jupiter.

Nature CommunicationsVol. 16(1)
Kanazawa University (JP), Centre National de la Recherche Scientifique (FR), Space Science Institute (US), Dublin Institute For Advanced Studies (IE), Swedish Institute of Space Physics (SE), Tohoku University (JP), Université Paris Cité (FR), Aix-Marseille Université (FR), Kyoto University (JP), Observatoire de Paris (FR), Johns Hopkins University Applied Physics Laboratory (US), Southern University of Science and Technology (CN), Kyung Hee University (KR), Sorbonne Université (FR), Sorbonne Paris Cité (FR), University of Southampton (GB), Nagoya University (JP), University of California, Berkeley (US)
Openalex Percentile: Top 75%
Ionosphere and magnetosphere dynamics
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