SCIENCE & NATURE

How does lightning actually form?

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Lightning forms when ice particles in storm clouds collide and create electrical charges that separate, building up until the charge difference becomes so large that it causes a giant spark between the cloud and ground. This spark is what we see as lightning.

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TemperatureLightning is about 5 times hotter than the surface of the sun
SpeedLightning travels at about one-third the speed of light
DurationA lightning bolt typically lasts less than one second
VoltageA single lightning strike can contain over 1 billion volts of electricity
Required conditionThunderstorms are necessary for lightning to form

How charge builds up in clouds

Inside a thunderstorm cloud, water droplets and ice particles bump into each other as they move around. When these particles collide, electrons are knocked loose from some particles and stick to others. This creates a separation of electrical charge. Lighter ice particles at the top of the cloud become positively charged, while heavier particles at the bottom become negatively charged. As more collisions happen, the charge difference keeps growing stronger and stronger.

When the charge becomes too strong

Eventually, the electrical difference between the cloud top and cloud bottom becomes so large that the air between them can no longer insulate them from each other. The negative charge at the bottom of the cloud starts to build up so much that it repels electrons in the ground below, making the ground positively charged. When the voltage gets high enough, it breaks through the air and creates a conducting path of plasma, which is ionized gas that allows electricity to flow.

The lightning strike

The lightning strike happens in stages. First, a step leader of negative charge moves down from the cloud toward the ground in steps. When it gets close to the ground, a streamer of positive charge moves upward to meet it. When they connect, a return stroke travels up the lightning channel and creates the bright flash we see. In many lightning strikes, multiple return strokes can travel up the same channel, making the lightning flicker.

Types of lightning

While cloud-to-ground lightning is the most famous and dangerous type, it only makes up about 25 percent of lightning strikes. Most lightning actually occurs within clouds or between clouds. Cloud-to-cloud lightning and intra-cloud lightning (lightning within a single cloud) are more common but we see them less clearly because they happen inside or between clouds.

Thunder and safety

Thunder is the sound created by lightning. The lightning channel heats the air so quickly to extreme temperatures that the air explodes outward, creating a shock wave we hear as thunder. You see lightning before you hear thunder because light travels much faster than sound. If you count the seconds between the flash and the thunder and divide by 5, you can estimate how many miles away the lightning is.

Sources

  1. noaa.gov (noaa.gov)
  2. weather.gov (weather.gov)
  3. nationalgeographic.com (nationalgeographic.com)