However, the most dramatic examples occur when long, bright lightning channels extend from the sides of cumulonimbus clouds. This refers to a discharge that jumps from a cloud into clear air and terminates abruptly – indeed, CG lightning contains CA lightning via the branches that extend from the main channel into the mid-air. Sprites (see side box) are usually associated with more intense positive CGs. Thunder from such lightning is very loud and may sound like a series of deep, low-frequency sonic booms. Positive cloud-to-ground lightning strikes are typically very bright (relative to other lightning activity) and can be identified by their distinct lack of branching near the ground. Such lightning is usually associated with supercell thunderstorms and trailing stratiform precipitation regions behind squall lines. Negative CG lightning strikes can be identified by their distinctive downward branching.Ī downward-moving initiates the less common CG flashes, positively-charged stepped leader, followed by an upward travelling return stroke that lowers the positive charge to earth. The net effect of this flash is to lower negative charge from the cloud to the ground. Negative Cloud-to-Ground Lightning (-CG)Ī downward-moving initiates the most common CG flashes, negatively-charged stepped leader, followed by an upward travelling return stroke. A return stroke (the very bright visible flash that we see as lightning) travels at about 60,000 miles per second back towards the cloud, with one flash consisting of as many as 20 return strokes. When the oppositely-charged leader and streamer connect, a powerful electrical current begins flowing (hence why it is ill-advised to stand under a tall object during a thunderstorm!). As it nears the ground, the negatively charged stepped leader is attracted to a channel of positive charge reaching up, a streamer, usually through something tall, such as a tree, house, or telephone pole. This stepped leader is invisible to the human eye and travels to the ground in a millisecond. In CG lightning, a channel of negative charge, called a stepped leader, will zigzag downward in a ‘forked’ pattern - hence it is sometimes called forked lightning. Lightning can strike the ground, the air, or inside clouds, but there are roughly 5 to 10 times more cloud flashes than cloud-to-ground flashes.

This, as well as its starting and ending points and direction of movement, give rise to different ‘types’ of lightning. The polarity of lightning discharge can affect how it spreads and branches in space and time. A beautiful and deadly natural phenomenon, lightning is simply a sudden, electrostatic discharge - a ‘spark’ or ‘flash’ as charged atmospheric regions temporarily equalise themselves through this discharge.

Sonic 1 sprite sheet