Cloud-to-cloud lightning, also known as intra-cloud (IC) lightning, refers to an electrical discharge that occurs between different charged regions within a cloud, or between two separate clouds, without ever striking the ground.
Understanding Cloud-to-Cloud Lightning
This common type of lightning illuminates the sky during thunderstorms, often appearing as a diffuse flash that lights up the cloud from within. It is a discharge of electricity that neutralizes the opposite charges built up within the vast atmospheric electrical generators that are thunderclouds.
Key Characteristics:
- No Ground Contact: The defining characteristic is that the discharge channel does not reach the Earth's surface. This distinguishes it from cloud-to-ground lightning, which poses a direct threat to people and structures.
- Intra-Cloud or Inter-Cloud: For the most part, cloud-to-cloud lightning occurs between oppositely charged portions of the same cloud. However, it can also take place between two distinct, separate clouds that are in close proximity.
- Charge Neutralization: Thunderclouds develop areas of separated electrical charges—typically positive charges accumulate in the upper parts and negative charges in the lower parts. When the electrical potential difference between these regions becomes too great, a sudden discharge occurs to equalize these charges, resulting in lightning.
How Cloud-to-Cloud Lightning Occurs
The formation of lightning, including cloud-to-cloud flashes, begins with the process of charge separation within a thunderstorm. Strong updrafts and downdrafts within a cumulonimbus cloud cause ice crystals, graupel (soft hail), and supercooled water droplets to collide. These collisions, particularly between smaller ice crystals (which tend to become positively charged) and larger graupel particles (which tend to become negatively charged), lead to charge separation.
- Upper Cloud: Accumulates positive charges due to lighter, positively charged ice crystals being carried upward.
- Lower Cloud: Develops a dominant negative charge due to heavier, negatively charged graupel falling to the bottom.
- Discharge: When the electrical stress between these oppositely charged regions within the cloud (or between two clouds) becomes too intense, the air's insulating properties break down. An electrical current then flows rapidly along a plasma channel, creating the brilliant flash we perceive as lightning.
Cloud-to-Cloud vs. Cloud-to-Ground Lightning
While both are forms of electrical discharge during a thunderstorm, their characteristics and impacts differ significantly.
| Feature | Cloud-to-Cloud (CC) Lightning | Cloud-to-Ground (CG) Lightning |
|---|---|---|
| Definition | Electrical discharge between areas of cloud or between two clouds. | Electrical discharge between a cloud and the Earth's surface. |
| Ground Contact | Does NOT reach the ground. | DOES reach the ground. |
| Typical Location | Within the same cloud or between distinct clouds. | Between the base of a cloud and the ground. |
| Visibility | Often appears as diffuse flashes illuminating the cloud from within ("sheet lightning"). | Appears as distinct, often brighter, visible bolts hitting the ground. |
| Frequency | More frequent globally than cloud-to-ground lightning, accounting for a significant majority of all lightning. | Less frequent but poses direct risk to life and property. |
| Associated Thunder | Thunder is often muffled or rolls for a longer period, due to the distance from the observer. | Thunder is usually sharp and loud, often a crack or boom, especially if nearby. |
Significance
Although cloud-to-cloud lightning does not directly strike the ground, its presence is a clear indicator of an active thunderstorm. It signifies significant electrical activity within the atmosphere and serves as a warning that cloud-to-ground lightning may also be occurring or could occur. Observing cloud-to-cloud flashes is a visual cue to seek shelter during severe weather events.
Understanding these different types of lightning helps in appreciating the powerful and complex dynamics of atmospheric electricity. For more information on lightning safety and thunderstorm phenomena, refer to resources from reputable meteorological organizations like the National Weather Service or the World Meteorological Organization.
