A radio oval above Earth’s auroral oval
Auroral kilometric radiation (AKR), Earth's strongest radio emission, has long been associated with discrete auroras and electrons near a few kilo-electron volt (keV) range. However, auroras also occur in diffuse forms with broader electron energies, raising the question of why AKR has not been observed above diffuse auroras or linked to electrons outside the kilo-electron volt population. Comprehensive AKR source distributions have remained elusive because of observational limitations, and their local-time coverage remains largely unknown. Using spacecraft measurements, we identify a "radio oval" above the optical auroral oval, spanning the full local-time range, where AKR is emitted over both discrete and diffuse auroras. The AKR source electrons display diverse precipitation features, including monoenergetic (peak flux at 3.82 kilo-electron volts), broadband (1.34 kilo-electron volts), low-energy (0.47 kilo-electron volts), and diffuse types (>1 kilo-electron volt). These results reveal that the cyclotron maser instability-the mechanism driving AKR-can arise in diverse plasma environments, broadening our understanding of both AKR generation and auroral complexity.
Authors
- Laurent Lamy (ORCID: https://orcid.org/0000-0002-8428-1369)
- Hao Ning (ORCID: https://orcid.org/0000-0001-8132-5357)
- X. L. Wang (ORCID: https://orcid.org/0009-0003-5457-4106)
- B. Collet (ORCID: https://orcid.org/0000-0003-1314-9632)
- Ulrich Taubenschuss (ORCID: https://orcid.org/0000-0003-4810-6958)
- Daniel Whiter (ORCID: https://orcid.org/0000-0001-7130-232X)
- Zhonghua Yao (ORCID: https://orcid.org/0000-0001-6826-2486)
- X. Luan
- Mengmeng Wang
- G. Fischer
- William Kurth
- Siyuan Wu
- Shengyi Ye
- Yao Chen
- Philippe Zarka
Institutions
- University of Iowa (US)
- University of Science and Technology of China (CN)
- Centre National de la Recherche Scientifique (FR)
- Planetary Science Institute (US)
- Swedish Institute of Space Physics (SE)
- University of Graz (AT)
- Tohoku University (JP)
- Université Paris Cité (FR)
- Aix-Marseille Université (FR)
- Observatoire de Paris (FR)
- Southern University of Science and Technology (CN)
- Sorbonne Université (FR)
- Institut des Sciences Moléculaires (FR)
- Sorbonne Paris Cité (FR)
- Institute of Space Sciences (ES)
- Czech Academy of Sciences, Institute of Atmospheric Physics (CZ)
- University of Southampton (GB)
- University of Hong Kong (HK)
Publication Details
- Journal
- Science Advances
- Published
- 2026-03-27
- DOI
- https://doi.org/10.1126/sciadv.aec4114
- Primary Topic
- Ionosphere and magnetosphere dynamics
- Type
- article
- Field-Weighted Citation Impact
- 0.00