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.