Blue jets are a unique type of lightning that appear to move in reverse, shooting up from thunderclouds and into the stratosphere at speeds of up to 50 kilometers per second. Unlike regular lightning, blue jets are known for their striking blue hue, which is created when they excite mostly stratospheric nitrogen gases.
Although blue jets have been observed from the ground and from aircraft for some time, understanding their formation requires a closer look from high above the clouds. In recent years, instruments on the International Space Station have provided scientists with the opportunity to study blue jets in more detail.
In a report published in Nature on January 20, researchers announced that they had finally captured a clear view of the spark that triggers a blue jet. Using cameras and light-sensing photometers, scientists were able to observe a blue jet emerging from a bright burst of electricity at the top of a thundercloud.
These upper-atmosphere phenomena, including blue jets, as well as sprites and elves, are significant because they can affect how radio waves travel through the air. This can have an impact on communication technologies, according to Penn State space physicist Victor Pasko.
During a storm over the Pacific Ocean near the island of Nauru in February 2019, the space station’s cameras and photometers captured a blue jet in action. The event began with a 10-microsecond flash of bright blue light near the top of the cloud, approximately 16 kilometers high. From that point, a blue jet shot up into the stratosphere, reaching altitudes as high as 52 kilometers over several hundred milliseconds.
Researchers believe that the spark that generated the blue jet may have been a special kind of short-range electric discharge inside the thundercloud. While normal lightning bolts are formed by discharges between oppositely charged regions of a cloud, the high-energy, short-range discharges that create blue jets occur when oppositely charged regions are brought within a kilometer of each other due to turbulent mixing high in the cloud. Evidence of these discharges has been seen in pulses of radio waves from thunderstorms detected by ground-based antennas.
The new observations of blue jets provide valuable insights into the dynamics of thunderstorms and the upper atmosphere, as well as the impact of these events on communication technologies.
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