Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: AGU Advances
Most auroras appear in the “auroral oval” at high latitudes surrounding the magnetic poles. However, some can appear as a detached auroral arc from the auroral oval, at lower latitudes in mid-afternoon and connected to the oval only at a tip or two. Such a detached arc is believed to be linked to the “plasmaspheric plume,” the tongue-shaped extension of the plasmasphere during the recovery phase of a geomagnetic storm. (The plasmasphere is the torus-shaped region of cold, dense plasma above the low- and mid-latitude ionosphere.) The surface waves at the plume boundary cause it to ripple and modulate the various plasma waves in the plume.
Based on observations from multiple satellites and ground stations, Feng et al. [2026] find sawtooth-like undulations along the equatorward boundary of a detached auroral arc in the ultraviolet that was produced by energetic (>keV) electrons and accompanied by energetic (>10 keV) ions. The authors attribute the undulations to Electromagnetic Ion Cyclotron (EMIC) waves that are modulated by the surface waves and resonating with the energetic ions. The study unravels the fine-scale structures of detached auroral arcs and sheds important light on the dynamics underlying their formation.
Citation: Feng, H., Wang, D., Hao, Y., Miyoshi, Y., Fu, H., Jun, C.-W., et al. (2026). First observation of sawtooth-like undulations in afternoon detached auroral arcs modulated by surface waves at the plasmaspheric plume boundary. AGU Advances, 7, e2025AV002234. https://doi.org/10.1029/2025AV002234
—Andrew Yau, Editor, AGU Advances