Positive lightning is a rare form of lightning that carries a positive charge to the ground, rather than the negative charge that is typically associated with lightning. This type of lightning can strike across very long distances, and with formidable power, making it extremely dangerous. It is often much more powerful than regular lightning, striking with as much as one billion volts of power.
Lightning is believed to be caused by a separation of electrical charges within a storm cloud. Typically, it emerges from the negatively charged base of a storm cloud in the form of a leader, which meets a positively charged streamer coming up from the ground. When the two connect, the result is a discharge of electricity from the cloud to the ground, causing a characteristic streak of light.
In the case of positive lightning, the charge comes from the positively charged top of a storm cloud, and it connects with a negatively charged streamer. This lightning can travel across 10 miles (16 kilometers) to meet a negatively charged streamer, releasing a burst of positively charged energy to the Earth. It is often associated with human activities, especially rocket launches and the testing of nuclear devices.
Since positive lightning is a unique phenomenon, special precautions must be taken to protect things like aircraft from it, as the protections that are normally effective against lightning are useless. People are also cautioned to beware of this phenomenon, which tends to strike more during heavy thunderstorms and at the end of a storm. As a general rule, it is a good idea for people to stay indoors for 30 minutes or so after a storm, allowing a storm to move away, and reducing the risk of being struck by lightning.
This type of lightning can travel across great distances, so it is not as predictable as other forms of lightning — which makes it more dangerous. It can also travel from cloud to cloud, also across great distances, and it may sometimes make a connection with the ground after traveling this way. The result can be a so-called “bolt from the blue”: a lightning bolt that strikes in seemingly fair weather.