The electron aurora forms a bright surge at the pole-ward boundary while the protons just show diffuse spreading. The peak intensity of the protons did not change substantially during the entire event. The proton aurora is brighter on the dusk while the electron aurora on the dawn side. As the electron surge expands pole-ward it leaves the protons behind. The electrons form a discrete auroral feature near the aurora-polar cap boundary, which is devoid of substantial energetic (>1 keV) proton precipitation.
Picture from IMAGE's far-ultraviolet instrument of the electron aurora over the North Pole on June 28, 2000
The coloured light display most people associate with the aurora or Northern Lights is produced by electrons crashing into the atmosphere as they descend along the Earth's magnetic field lines. Almost equally bright but less structured are the lights produced by positively charged protons - hydrogen nuclei - as they ram the atmosphere.
