5. Blue Bolts: The Azure Streaks of Intra-Cloud Lightning
A kind of intra-cloud lightning, blue bolts show up as brilliant blue streaks within thunderstorms. Under some circumstances, these electric discharges—which occur across areas of opposite charge inside the same cloud—cause amazing blue light displays observable from the ground.
The great energy of the electrical discharge and its interaction with nitrogen molecules in the atmosphere give these bolts their blue hue. Nitrogen molecules ionise as the lightning passes across the cloud, then release blue light as they return to their ground state.
The fast heating and expansion of the air along the lightning channel causes a characteristic crackling sound accompanying blue bolts. Although blue bolts are not as frequently as some other blue lightning events, their strong azure brightness and complex branching patterns enthrals viewers.
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.