Types of Lightning
Contrary to the common expression, lightning can and often does strike the same place twice!
Lightning is an electrical discharge caused by imbalances between the thunderstorm and another cloud, ground or object. There are roughly 5 to 10 times as many flashes that remain in the cloud as there are flashes which travel to the ground. Lightning can strike where it’s not raining, or even before rain reaches the ground! Let’s examine the different types of lightning.
Cloud-to-Ground (CG) Lightning
A channel of negative charge, called a stepped leader, will zigzag downward in a forked pattern. This stepped leader is invisible to the human eye and shoots to the ground in less time than it takes to blink. As it nears the ground, the negatively charged stepped leader causes streamer channels of positive charge to reach upward, normally from taller objects in the area, such as a tree, house or telephone pole.
When the oppositely charged leader and streamer connect, a powerful electrical current begins flowing. This return stroke of current of bright luminosity travels around 60,000 miles per second back towards the cloud.
Negative Cloud-to-Ground Lightning (-CG):
- The most common type of cloud-to-ground flashes.
- It has a negative stepped leader that travels downward through the cloud, followed by an upward traveling return stroke. The net effect of this flash is to lower a negative charge from the cloud to the ground.
- Negative CG lightning strikes can be identified by their distinctive downward branching.
- A downward traveling positive leader followed by an upward return stroke will lower positive charge to earth.
- Usually associated with supercell thunderstorms and trailing stratiform precipitation regions behind squall lines.
- Is typically very bright (relative to other lightning activity) and can be identified by their distinct lack of branching near the ground.
- Thunder from such lightning is very loud and may sound like a series of deep, low-frequency sonic booms.
This refers to a discharge that jumps from a cloud into clear air and terminates abruptly. CG lightning can contain CA lightning via the branches that extend from the main channel into mid-air. However, the most dramatic examples occur when long, bright lightning channels extend from the sides of cumulonimbus clouds.
Intra-Cloud (IC) Lightning
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.
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. Although often associated with IC lightning, it is any lightning hidden by clouds or terrain aside from the flash of light it produces.
A related term, heat lightning, is any lightning or lightning-induced illumination too far away for thunder to be heard. Heat lightning got its name because it is often seen on hot summer nights when thunderstorms are common.
Cloud-to-Cloud (CC) Lightning
Although rare, lightning can also travel from one cloud to another or more. Spider lightning refers to long, horizontal moving flashes often seen on the underside of stratiform clouds.
Ground-to-Cloud (GC) Lightning
An upward-moving leader initiates a discharge between cloud and ground from an object on the ground. Ground-to-cloud lightning strikes - sometimes called upward-moving lightning - are common on tall towers and skyscrapers. GC lightning can also be either positive or negative in polarity. Lightning that demonstrates upward branching indicates a ground-to-cloud flash, though some upward-moving lightning is branchless below the cloud base.
Source: NOAA, National Geographic, Royal Meteorological Society
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