Astrophotographers help crack mystery of ‘sprite fireworks’

On May 19, 2022, two astrophotographers set up near the sacred lake of Pumoyongcuo on the southern Tibetan Plateau captured a vibrant display streaking across the Himalayan sky. Over a single night, Angel An and Shuchang Dong recorded over 100 red sprites, bursts of brilliantly colorful electrical discharges known for both their color and ethereal patterns. Rarely seen secondary jets also joined the atmospheric phenomena, as well as the first-known images in Asia of ghost sprites—greenish glowing that is sometimes seen near the base of an evening’s ionosphere. One of the photos was so striking that it even went on to win the “Skyscapes” category of the Royal Observatory Greenwich’s 2023 Astronomy Photographer of the Year competition.

While these dramatic “sprite fireworks” displays are well-known, little is understood about how and why they form. However, researchers at China’s University of Science and Technology are beginning to unravel red sprite behavior thanks in part to the astrophotographers’ work. Their results, published in Advances in Atmospheric Sciences, illustrate the complex celestial interactions that can occur far above us.

Before they began to study the Himalayan red sprites, Gaopeng Lu and his colleagues encountered a problem: While visually arresting, An and Dong’s recordings of the 2022 outbreak weren’t timestamped. Without these reference points, Lu’s team could not match the sprites to their parent lightning discharges. They came up with a creative workaround: While they didn’t know exactly when the sprites occurred, they could figure out where they formed in the night sky. By matching the coordinates of 95 of the sprites with multiple orbital satellite trajectories and star chart positions, researchers managed to pinpoint each electrical event’s time to within a one second margin of error. From there, they could link around 70 percent of the red sprites to their parent lightning events, then examine those discharges.

“This event was truly remarkable,” said Gaopeng Lu in an accompanying statement. “By analyzing the parent lightning discharges, we discovered that the sprites were triggered by high-peak current positive cloud-to-ground lightning strikes within a massive mesoscale convective system.”

A mesoscale event is a large complex of thunderstorms that include weather systems like lake-effect snow, squall lines, and tropical cyclones, depending on their location. In the case of the May 2022 event, the sprites formed inside an area stretching over 77,220 square miles from the Ganges Plain of northeast India to the Tibetan Plateau’s southern foothills. It also featured the highest number of sprites ever recorded in South Asia, most of which featured a positive polarity with peak currents topping +50 kiloamperes (kA).

Lu and his team now believe thunderstorms in the Himalayas may produce some of Earth’s “most complex and intense upper-atmospheric electrical discharges” that are likely on par to those documented in the US Great Plains and off European coasts. The team’s findings also have important implications for how experts can better characterize regional thunderstorms in the future, including how their physical and chemical attributes affect adjacent areas. 

Their novel timestamping approach isn’t limited to red sprite revelations, either. Any citizen scientist with the right know-how can now also use the study’s methodology for their own meteorological work.

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