Upside-Down Lightning Shoots Towards Space
Just how giant jet lightning forms has been revealed after detailed analysis of two events by researchers at Duke University.
The scientists examined two giant jet lightning bolts, one in Florida and one in Oklahoma, both of which shot at least 50 miles (80 kilometers) into the sky.
They tracked very high frequency (VHF) radio emissions to understand how the bolts formed in 3-D, and also analyzed their magnetic fields to measure their charge.
The amount of electricity discharged by jets compared with normal lightning is about the same. Both get their electric charge from thunderstorms and are formed from normal lightning between clouds.
However, there are differences: normal lightning travels down to Earth, while jets travel up to the ionosphere; and jets travel further and faster due to lower air resistance between the clouds and ionosphere, following multiple channels compared with a single channel for downward lightning.
Lightning usually occur in tropospheric clouds, the lowest region of the atmosphere, which has an upper positive charged portion and a lower negatively charged portion. The potential difference between the two portions prevents the lightning from escaping up above the cloud.
“Our measurements show that gigantic jets are capable of transferring a substantial electrical charge to the lower ionosphere,” said study leader Steven Cummer in a press release.
“They are essentially upward lightning from thunderclouds that deliver charge just like conventional cloud-to-ground lightning," he added. "What struck us was the size of this event."
Both cases began as normal lightning interactions between clouds. However, when the upper positively charged portion of the clouds was depleted, the lightning shot up into the ionosphere—a positively charged region produced by the sun’s ultraviolet radiation reacting with air molecules.
There are two hypotheses as to how the upper portion dissipates: lightning depletes the upper layers preceding the formation of a giant jet, or the upper region is neutralized by mixing with the uppermost negative screening layer.
The findings were published in Geophysical Research Letters on June 20.
