6. Blue Elves: Ring-Shaped Wonders in the Ionosphere
Another amazing blue lightning event high in the Earth’s atmosphere are blue elves, short for Emission of Light and Very Low Frequency disturbances owing to Electromagnetic Pulse Sources. Usually found in the ionosphere, these ring-shaped flashes of light span 80 to 100 kilometres.
Elves are not directly caused by lightning strikes unlike other blue lightning events. Rather, the electromagnetic pulse produced by strong cloud-to- ground lightning sets off them. In the lower ionosphere this pulse generates a fast expanding disc of ionisation and light emission.
The blue hue of elves comes from the electromagnetic pulse’s stimulation of nitrogen molecules. Blue light emitted by these molecules de-excites them to produce the distinctive ring form that stretches outward almost at the speed of light. With their few hundred microseconds, elves are quite fleeting and difficult to view with the unaided eye.