Throughout history, humans have been mystified by lightning, and many myths have
evolved throughout the centuries. Even today, scientists are still studying lightning
to find out exactly what exactly happens during a flash of lightning. Learn some of the
basics about thunderstorm development and lightning.
Lightning is fascinating to watch but also extremely dangerous. In the United States, there are about 25 million lightning flashes every year. Each of those 25 million flashes is a potential killer. While lightning fatalities have decreased over the past 30 years, lightning continues to be one of the top weather killers in the United States. In addition, lightning injures many more people than it kills and leaves some victims with life-long health problems.
All thunderstorms go through stages of growth, development, electrification and dissipation. Thunderstorms often begin to develop early in the day when the sun heats the air near the ground and pockets of warmer air start to rise in the atmosphere. When these pockets of air reach a certain level in the atmosphere, cumulus clouds start to form. Continued heating causes these clouds to grow vertically into the atmosphere. These "towering cumulus" clouds may be one of the first signs of a developing thunderstorm. The final stage of development occurs as the top of the cloud becomes anvil-shaped.
As a thunderstorm cloud grows, precipitation forms within the cloud. A well-developed thunderstorm cloud contains mostly small ice crystals in the upper levels of the cloud, a mixture of small ice crystals and small hail in the middle levels of the cloud, and a mixture of rain and melting hail in the lower levels of the cloud. Air movements and collisions between the various types of precipitation in the middle of the cloud cause the precipitation particles to become charged. The lighter ice crystals become positively charged and are carried upward into the upper part of the storm by rising air.
The heavier hail becomes negatively charged and is either suspended by the rising air or falls toward the lower part of the storm. These collisions and air movements cause the top of
the thunderstorm cloud to become positively charged and the middle and lower part of the storm to become negatively charged.
Lightning is a giant spark of electricity in the atmosphere or between the atmosphere and the ground. In the initial stages
of development, air acts as an insulator between the positive and negative charges in the cloud and between the cloud and the ground; however, when the differences in charges becomes too great, this insulating capacity of the air breaks down and there is a rapid discharge of electricity that we know as lightning.