First Observations of Terrestrial Gamma-Ray Flashes Made by Researchers

Ground-breaking research from a team in Japan has revealed that gamma-ray flashes, previously thought to only occur in space, can also happen on Earth. This discovery is particularly significant as it marks the first time scientists have captured the formation of such flashes during thunderstorms.

Gamma-ray bursts typically originate in space, often resulting from cataclysmic events such as stellar explosions. These cosmic phenomena release an astonishing amount of energy in a matter of seconds, surpassing the total energy output of the Sun throughout its lifespan. However, a less intense variant known as terrestrial gamma-ray flashes (TGFs) has been identified on Earth since the mid-1990s when they were first detected by a satellite.

The latest observations were conducted by researchers at Osaka University, who detailed their findings in the journal Science Advances. Led by Yuuki Wada, the team established a monitoring system equipped with various sensors on two television towers in Kanazawa, Japan. This setup was designed to detect a wide range of radiation, from radio waves to visible light and gamma radiation.

On January 30, the sensors recorded a lightning strike hitting one of the towers. During this event, two discharge paths were created: one negatively charged path moving from the cloud to the ground and a positively charged path from the ground upward. When these paths converged, a discharge occurred.

In this specific case, the discharge, which reached a current of 56 kiloamperes, took place at an altitude of just under one kilometer. Remarkably, the gamma-ray flash occurred mere fractions of a second before the discharge paths met, with the sensors detecting gamma radiation 31 microseconds prior to the discharge. The entire TGF event lasted approximately 20 microseconds.

According to Harufumi Tsuchiya, a senior author of the study, this multi-sensor observation is a world-first achievement. While several mysteries remain, this innovative technique has brought researchers closer to understanding the mechanisms behind these intriguing radiation bursts. The findings provide critical insights into how lightning generates enough energy to produce gamma rays.

Previous observations of TGFs were conducted from space, where satellites could cover vast areas without interference from atmospheric absorption of gamma radiation. However, those observations lacked precision. In the past year, two studies published in Nature described TGFs occurring in tropical storms, based on data collected from modified surveillance aircraft that flew into the storm systems.

Wada noted that while these aerial observations are fascinating, ground-based monitoring offers a more cost-effective approach to studying these phenomena.