7. “Sprites” and “Elves” Dance Above Thunderstorms
Ethereal and transient light displays known as sprites and elves arise high above the thunderclouds in the upper reaches of Earth’s atmosphere. Often shaped like jellyfish or columns, sprites are large-scale electrical discharges that show as reddish-orange flashes. Conversely, elves are fast spreading rings of light covering hundreds of kilometres. Though anecdotal evidence going back millennia, these events—collectively known as Transient Luminous Events (TLEs)—were only formally recorded in 1989. In the mesosphere and lower ionosphere, areas of the atmosphere challenging direct study, sprites and elves abound. Their discovery has transformed our knowledge of the worldwide electrical circuit as well as the intricate interactions among several levels of the environment. Investigating these upper-atmospheric lightning events affects climate research, space weather prediction, even the hunt for livable exoplanets. Some researchers hypothesise that sprites and elves may impact chemical reactions in the upper atmosphere or help to generate some kinds of clouds, therefore influencing Earth’s ozone layer and general temperature.