How Lightning Hits the Ground

Atmospheric Charge

• The Earth's atmosphere is filled with electrical charge. This charge is created by positively and negatively charged ions. During normal conditions, these ions are uniformly distributed. This provides little potential for electrical discharges, known as lightning. Therefore, the first ingredient needed to produce a lightning bolt is a mechanism for separating the charged ions.

Thunderstorms

• Nature's mechanism for separating negative and positive ions is the thunderstorm. Within the updraft, positively charged ice crystals rise. Within the downdraft, negatively charged hail stones, also known as graupel, descend. This creates a positively charged layer at the top of the thunderstorm and a negatively charged layer at its base. At the same time, positively charged ions begin to form along the surface beneath the cloud, attracted to its negatively-charged base.

Stepped Leaders

• As the negative charge builds in the base of the cloud, negative ions begin to be drawn towards the positively charged ground in stepped leaders. These leaders travel approximately 50 yards at a time, pausing between steps. They can shift direction toward stronger electric fields and branch. As the leader nears the ground, a powerful electric potential develops, on the order of around 10 million volts. This causes positively charged ions on the ground to begin surging upwards toward the negative stepped leaders.

The Lightning Bolt

• The stepped leaders and upwardly surging positive ions meet at between 30 to 120 feet in the air. At the moment they connect, an electrical discharge occurs, sending a return stroke back up to the cloud. This stroke is the visible flash of the lightning bolt, caused by the super-heating of the air to 54,000 degrees Fahrenheit. The bolt travels upward at around 60,000 miles per second.

Dart Leaders

• Once the return stroke reaches the cloud, additional negative ions at the top of the channel can take advantage of the path that was formed. They descend as dart leaders. Unlike stepped leaders, their path is continuous and up to 10 times faster. As the dart leader connects with the positive ions at the base of the channel, additional return strokes are created. A typical lightning bolt is comprised of four to 10 strokes. These strokes are about 0.05 seconds apart. This is just within the range of perception for your eyes, and appears as a flicker.