The familiar glow of the aurora begins when solar particles are guided by Earth's magnetic field into the upper atmosphere, where they strike atoms and molecules and emit light. While the overall mechanism is well understood, the smallest details of auroral curtains have resisted easy explanation. A new analysis of ground-based optical measurements offers a possible answer: some fine structures may be produced by electrons that bounce off low-frequency plasma waves, known as Alfvén waves, high above the ionosphere.
Brindley and Whiter used the Auroral Structure and Kinetics (ASK) instrument in Svalbard, Norway, to observe oxygen and nitrogen emissions in optical and near-infrared wavelengths. The instrument tracked how electric fields changed over a 25-second interval, a span long enough to catch variations that satellites often miss because they pass through the region only briefly. The team then mapped the electric fields using two independent approaches, one of which assumed a U-shaped electric potential above the arc.
The two mappings were largely consistent. Where they differed, the researchers suggest the discrepancy could be explained by electrons accelerated as they bounce off Alfvén waves. That interpretation ties the observed fine-scale auroral structure to wave-particle interactions rather than to static electric fields alone.
Because the method relies only on optical data with high spatial and temporal resolution, it could be applied more widely to study small-scale auroral dynamics and other space weather phenomena, the authors propose.