At www.spaceweather.com Monday Aug 1 2016 … it seems a mysterious form of aurora can be seen on occasion, known as the proton arc. The image below was taken in Alberta. These are tight ribbons of light that pulse and dance with the northern lights
Scientists say they probably have nothing to do with protons as proton aurora behaves differently – and does not seem to take a tight form. Instead, proton aurora is rather loose and tends to circle around magnetic fields in lazy arcs. As they occupy the UV light spectrum proton aurora are very often invisible – or barely visible (even though they form large circles). Common aurora are caused by electrons precipitating down into the atmosphere.