Auroral structure could be caused by bouncing electrons
The aurora is among nature's most visually striking phenomena. It occurs when charged particles from the sun are funneled by Earth's magnetic field into the upper atmosphere, where they collide with atoms and molecules and produce distinctly colored curtainlike patterns of light.
Auroras, stunning displays of light in Earth's upper atmosphere, result from charged particles from the sun colliding with atmospheric atoms and molecules. While the physics behind auroras is well understood, some small-scale features remain puzzling. Researchers N. Brindley and D. Whiter have discovered that certain fine auroral structures could be caused by electrons bouncing off low-frequency plasma waves, known as Alfvén waves, above the ionosphere.
To investigate this, the researchers utilized high-resolution optical data and a simple mathematical model. They focused on oxygen and nitrogen emissions in the optical and near-infrared spectrum, collected by the ground-based Auroral Structure and Kinetics (ASK) instrument during a deployment in Svalbard, Norway. The ASK instrument provided valuable spatial and temporal data on how electric fields evolved over a 25-second period, long enough to capture behavior often missed by satellite-based studies.
The researchers employed two methods to map electric fields, one assuming the existence of a U-shaped potential. The results from both methods were largely consistent, except for slight discrepancies that could be explained by electrons being accelerated by bouncing off Alfvén waves above the ionosphere. This mechanism appears to be a plausible explanation for the fine auroral structures that have proven challenging to understand.
The optical-only observation method with high spatial and temporal resolution offers a promising approach for studying auroras and other space weather phenomena at small scales. The findings of Brindley and Whiter are published in the Journal of Geophysical Research: Space Physics, providing a new perspective on the complex interplay of plasmas and electromagnetic fields in the aurora.
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