Scientists have finally gotten a clear view of the spark that sets off a weird type of lightning called a blue jet.
Lightning bolts usually are seen zipping from thunderclouds down toward the ground. But blue jets shoot up from clouds. They ascend high into a layer of the atmosphere called the stratosphere. In less than a second, a blue jet can reach about 50 kilometers (31 miles) above the ground. In the stratosphere, this electricity excites mostly nitrogen gas. That nitrogen glows blue, giving these jets their signature color.
Blue jets have been seen from the ground and airplanes for years. But it was hard to tell how this weird lightning formed without seeing it from above. So scientists looked for a blue jet using the International Space Station. And they spotted one in February 2019. It appeared above a storm over the Pacific Ocean near Australia. Using cameras and other sensors on the space station, scientists could see how the blue jet formed.
“The whole thing starts with what I think of as a blue bang,” says Torsten Neubert. He studies the physics of the atmosphere at Technical University of Denmark in Kongens Lyngby.
What Neubert calls a “blue bang” was the flash of bright blue light near the top of the storm cloud. That burst of electricity lasted just 10 millionths of a second. But from it the blue jet was born. The jet started at the top of the cloud, about 16 kilometers (10 miles) up. From there it climbed into the stratosphere. It rose as high as 52 kilometers (32 miles) and lasted about half a second. Neubert’s team described the jet’s origins online January 20 in Nature.
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The spark that caused the blue jet may have been a special type of electric event inside the cloud, Neubert says.
Lightning forms when electric current runs between oppositely charged parts of a cloud — or between the cloud and the ground. Those regions of opposite charge are usually many kilometers apart. But chaotic airflow high in a cloud may bring oppositely charged regions close together. Say, within about one kilometer (0.6 mile) of each other. That could create a very short, but powerful surge of electric current, Neubert says. Such a brief, intense burst of electricity could create a blue flash like the one that generated the blue jet.
Understanding blue jets better may have practical use, says Victor Pasko at Pennsylvania State University in University Park. He was not involved in the study. But as a space physicist, he studies such atmospheric phenomena. Storms can trigger a number of these, including sprites and elves. These atmospheric events can affect how radio signals travel through the air, he notes. Such signals connect satellites with devices on the ground. Among other things, satellites provide the GPS coordinates for navigation on smartphones and other electronics.