Lightning. Most of us have seen or felt the often dramatic and sometimes terrifying gigantic bolts of electricity streaking through the sky during a thunderstorm.
It may surprise people to know that for as long as scientists have studied lightning, it's still a bit of a mystery how, exactly, lightning forms.
In May, researchers at the Florida Institute of Technology filmed the video below. They're using a high-speed camera to capture amazing lightning flashes -- downward ones from thunder clouds, as well as rare upward lightning discharges.
These striking videos -- with their real-time speed slowed down -- show multi-bursts of lightning seeming to crawl down (or up!) and opening out into menacing, claw-like appendages, culminating with huge bursts of electrical, bomb-like images. Yet each of the lightning events in the videos lasted less than one second.
"We know lightning exists, but it seems that the electric field is not large enough for lightning to get initiated," according to physicist and principal investigator Ningyu Liu, of FIT's Geospace Physics Laboratory in Melbourne, Florida.
"Lightning is an electrical discharge process and we know, to start lightning, we need a very large electric field, which can accelerate free electrons inside the cloud. But so far, from measurements, it seems the electric field inside the thunder clouds is actually not that large. Certainly it doesn't exceed the threshold value to start electrical breakdown," Liu told The Huffington Post.
Liu explains why it's still a mystery how lightning begins.
"It's a very complex process because it's difficult to send electric field sensors in the right region at the right moment," Liu said. "Ideally, we want to put a sensor right before the lightning is initiated to measure the field inside the thunder cloud. But it's very difficult to do that. We can't predict when lightning will begin, where it will propagate and which object on the ground it will strike."
The National Severe Storms Laboratory, located in Norman, Oklahoma, confirms the ongoing mystery over lightning formation:
"Lightning is a giant spark of electricity in the atmosphere between clouds, the air, or the ground. In the early stages of development, air acts as an insulator between the positive and negative charges in the cloud and between the cloud and the ground. When the opposite charges build up enough, this insulating capacity of the air breaks down and there is a rapid discharge of electricity that we know as lightning.
"The creation of lightning is a complicated process. We generally know what conditions are needed to produce lightning, but there is still debate about exactly how a cloud builds up electrical charges and how lightning forms."
Adding to the unknown factor of lightning is the occasional rare moment when nature's electrical outburst moves up instead of down.
The following video shows some of the scarce upward lightning videotaped by Liu and his team:
"Sometimes lightning can propagate upward from the thunder cloud tops. It can reach 60 to 70 kilometers [about 40 miles] into the low ionosphere," said Liu, referring to a conducting layer of the upper atmosphere that helps transmit radio signals around the world.
"For some communication systems, we use this layer to propagate signals from point A to point B. If this ionosphere is modified by upward lightning, then it can produce some disturbances in the communications signals."
Here are more examples of upward lightning from a previous Discovery Channel program, "Raging Planet":
As fascinated as Liu is researching the mystery of lightning, he cautions everybody not to put themselves in harm's way as a storm approaches.
"Lightning, of course, carries a lot of current, charge and voltage," he says. "When current flows through an object, it can produce a lot of heat, which can really cause serious damage.
"So, I don't want to be nearby any strike recorded on the video."