When there is little change in form and brightness during a display, the aurora is said to be “quiet”. However, any of the auroral forms may by “pulsating”, indicated by fading and brightening, or disappearing and reappearing rhythmically. An aurora is “flickering” when it displays subtle but irregular rapid changes. An aurora is “flaming” when waves of light move rapidly upwards, lighting up existing forms. An aurora is “streaming” when it displays irregular horizontal variations, such as a brighter area rippling horizontally along a band.