Auroras are associated with the solar wind, a flow of ions continuously flowing outward from the sun. The Earth´s magnetic field traps these particles, many of which travel toward the poles where they are accelerated toward Earth.
Collisions between these ions and atmospheric atoms and molecules causes energy releases in the form of auroras appearing in large circles around the poles. Auroras are more frequent and brighter during the intense phase of the solar cycle when coronal mass ejections increase the intensity of the solar wind. Seen from space, these fiery curtains form a thin ring in the shape of a monk´s tonsure.
The Northern Lights occur high above the surface of the earth where the atmosphere has become extremely thin, in an altitude of 100-250km.