The images show, Frey said, that the diffuse aurora at lower polar latitudes comes from both protons and electrons, while the very pretty, structured aurora at higher latitudes near the North Pole is due almost entirely to the electrons. Substorms are generated when the Earth's magnetosphere for some reason gets charged up with protons and electrons and then discharges, sending ionized particles spiraling along magnetic field lines to where they converge at the pole. Along the way, they hit atoms in the atmosphere and emit light, ranging from colorful visible light to the invisible far-ultraviolet. Substorms, which may last an hour, are distinct from the day-long storms, which are generated by coronal mass ejections and large flares on the sun, which disrupt global communications. What makes the two types of auroras distinct are the different behaviors of protons and electrons as they enter the atmosphere.
Protons quickly become neutralized as they combine with electrons.
Once this happens they ignore magnetic field lines and fly in all directions. Electrons, however, remain free and stick to magnetic field lines. As a result, the light from their collisions with atmospheric atoms has a structure dictated by the field lines, typically shimmering curtains of light. As the electron aurora continued to expand toward the pole, the proton aurora remained behind. By studying the two separately, we are beginning to understand the dynamics of the Northern Lights.