Winter storms usually produce the greatest proportion of CG flashes in the UK. These high cloud base storms tend to have greater IC flashes. These thunderstorms tend to produce significant lightning due in part to their high cloud bases, which increase the amount of water in ice form, necessary for strong electrical charging. The most spectacular displays of lightning in the UK are generally associated with “Spanish Plume” type events, especially since these can occur during the night. (Not to be confused with intracloud lightning within a single cloud). Spider lightning refers to long, horizontal moving flashes often seen on the underside of stratiform clouds. Cloud-to-Cloud (CC) Lightning (or intercloud lightning)Īlthough rare, lightning can also travel from one cloud to another (or more!). Heat lightning got its name because it is often seen on hot summer nights when thunderstorms are common. Although often associated with IC lightning, it is any lightning hidden by clouds or terrain aside from the flash of light it produces.Ī related term, heat lightning, is any lightning or lightning-induced illumination too far away for thunder to be heard. Sheet Lightning is a term used to describe clouds illuminated by a lightning discharge where the actual lightning channel is either inside the clouds or below the horizon (i.e. This is the most common type of discharge and refers to lightning embedded within a single storm cloud, which jumps between different charge regions in the cloud. Lightning that demonstrates upward branching indicates a ground-to-cloud flash, though some upward-moving lightning is branchless below the cloud base. GC lightning can also be either positive or negative in polarity. Ground-to-Cloud lightning strikes - sometimes called upward-moving lightning - are common on tall towers and skyscrapers. Ground-to-Cloud (GC) LightningĪn upward-moving leader initiates a discharge between cloud and ground from an object on the ground. 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.
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