Cloud to Ground Electrical Discharge Sequence

A cloud-to-ground electrical discharge, commonly known as lightning, follows a specific sequence of events to establish a path and discharge electricity. Understanding this sequence is key to comprehending lightning formation.

1. Stepped Leader Progression

The discharge typically begins with a stepped leader. This is an initial channel of ionized air that moves downward from a cloud towards the ground. It travels in discrete steps, pausing briefly between each advance as it searches for the most conductive path.

2. Streamer Formation and Connection

As the negatively charged stepped leader approaches the ground, the strong electric field near the surface causes positive charges within the ground or objects on it to rise, forming upward-moving channels called streamers. When a streamer meets the descending stepped leader, the conductive path between the cloud and the ground is completed.

3. Return Stroke Event

Once the path is established, a powerful surge of electrical current flows rapidly upward from the ground along the ionized channel. This is the return stroke, which constitutes the main, bright flash of lightning visible to the observer.

4. Dart Leader Phase

After the initial return stroke, the lightning channel may remain ionized. If there is still a significant charge difference between the cloud and the ground, another leader, known as a dart leader, can rapidly descend through the existing channel. Unlike the stepped leader, the dart leader moves continuously.

This dart leader can then initiate subsequent return strokes, leading to multiple flashes within a single lightning event.