Where does lightning come from?

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Understanding the Origins of Lightning

Lightning is a fascinating and complex natural phenomenon that has intrigued scientists for centuries. This article synthesizes current research to explain where lightning comes from, focusing on its formation, types, and the conditions that lead to its occurrence.

Formation of Lightning: Meteorological Concepts

Lightning originates in clouds with tops colder than freezing, typically between -5°C and -15°C (23°F and 5°F). Updrafts within thunderstorms transport moist air to higher altitudes where it cools and forms ice crystals. The interaction between these ice crystals and supercooled water droplets leads to the separation of electric charges within the cloud. This charge separation is crucial for lightning formation, as it creates the electric fields necessary for a discharge.

Types of Lightning: Cloud-to-Ground and Intra-Cloud

There are several types of lightning, with the most common being cloud-to-ground (CG) and intra-cloud (IC) lightning. CG lightning occurs when a discharge travels between the cloud and the ground, while IC lightning happens within the cloud itself. Research shows that thunder, the sound produced by lightning, predominantly originates from the return strokes of CG lightning, which are more energetic than IC discharges.

Positive Cloud-to-Ground Lightning

Positive cloud-to-ground (+CG) lightning is a specific type of CG lightning that carries a positive charge. Studies have shown that +CG lightning often originates in the stratiform region of mesoscale convective systems (MCS). In these systems, +CG lightning can initiate in the leading convective line and propagate rearward before striking the ground. This horizontal propagation through vertically thin layers of stratiform charge acts as a conduit for +CG lightning.

Upward Electrical Discharges

In addition to the more common downward lightning, thunderstorms can also produce upward electrical discharges, such as blue jets and gigantic jets. These discharges propagate from the top of the storm towards the ionosphere. Blue jets occur due to electrical breakdown between the upper storm charge and the screening charge at the cloud top, while gigantic jets start as normal IC discharges that extend out of the storm.

Lightning in the Solar Nebula

Interestingly, lightning is not confined to Earth's atmosphere. Research suggests that lightning could have played a role in the early solar system, particularly in the formation of chondrules within meteorites. A model proposes that triboelectric charging of particles in the solar nebula could generate strong electric fields, leading to lightning discharges capable of melting and forming chondrules.

Conclusion

Lightning is a complex process that involves the interaction of various meteorological and electrical factors. It originates in clouds with freezing temperatures, where charge separation occurs due to updrafts and the interaction of ice crystals and water droplets. Different types of lightning, including CG, IC, and upward discharges, highlight the diverse ways in which electrical energy can be released during thunderstorms. Additionally, the concept of lightning extends beyond Earth, potentially playing a role in the early solar system. Understanding these processes helps demystify one of nature's most spectacular displays.