Scientists have now captured a clear image of the spark that causes an unusual sort of lightning known as a blue jet.
Blue jets shoot up from thunderclouds into the stratosphere in less than a second, reaching altitudes of up to 50 kilometers. Unlike conventional lightning, which excites a variety of gases in the lower atmosphere to produce a white glow, blue jets excite primarily stratospheric nitrogen to produce their trademark blue tint.
For years, blue jets have been witnessed from the ground and from aircraft, but it’s difficult to discern how they arise without flying high above the clouds. The International Space Station’s detectors have now detected a blue jet emerging from an incredibly brief, dazzling blast of electricity near the top of a thundercloud.
Understanding blue jets and other upper-atmosphere thunderstorm phenomena like sprites (SN: 6/14/02) and elves (SN: 12/23/95) is important because these events can affect how radio waves travel through the air, potentially affecting communication technologies, according to Penn State space physicist Victor Pasko, who was not involved in the work.
Amid February 2019, space station cameras and light-sensing sensors known as photometers witnessed the blue jet in a storm over the Pacific Ocean near the island of Nauru. “I think of it as a blue bang,” says Torsten Neubert, an atmospheric scientist at the Technical University of Denmark in Kongens Lyngby. That “blue explosion” was a 10-microsecond flash of intense blue light near the cloud’s apex, some 16 kilometers above the ground. A blue jet surged up into the stratosphere from that position, reaching a height of around 52 kilometers in a few hundred milliseconds.
According to Neubert, the spark that formed the blue jet could have been a specific type of short-range electric discharge within the thundercloud. Normal lightning bolts are created by discharges between oppositely charged parts of a cloud — or between a cloud and the earth — that are thousands of kilometers away. However, chaotic mixing high in a cloud can put oppositely charged regions within a kilometer of each other, resulting in very short but intense bursts of electric current, according to Neubert. Researchers have discovered evidence of such high-energy, short-range discharges in radio wave pulses intercepted by ground-based antennas from thunderstorms
