New Florida Tech Research is Investigating Gamma Ray Flashes

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When lightning flashes across the sky in one of Mother Nature’s most thrilling performances, there is in fact much more to these bright bolts than meets the eye, researchers at Florida Tech are learning.

In an article recently published in Nature Scientific Reports, Florida Tech’s Amitabh Nag, an associate professor in aerospace, physics and space sciences, along with first author, Bagrat Mailyan, a former post-doctoral research associate at Florida Tech, and Hamid Rassoul, a Distinguished University Professor at Florida Tech, reported on their analysis of a massive dataset of 2,188 terrestrial gamma ray flashes (TGFs) emitted from thunderstorms. The signatures of these flashes were measured simultaneously using the space-based Fermi Gamma-ray Burst Monitor and the ground-based Global Lightning Dataset (GLD360) over a five-year period.

TGFs are bursts of gamma-ray photons (akin to energy bundles) that generally last for less than one-thousandth of a second and are the most energy-packed natural emissions on Earth. In addition to studying this energetic radiation, Nag and his team is looking at the high-amplitude electromagnetic pulses (EMPs) that are also emitted by these TGFs.

High-amplitude EMPs could affect a variety of both ground-based and airborne infrastructure, such as power lines and aircrafts.

Maps showing (a) locations of TGF-associated EMPs reported from ground, (b) TGFs density detected from space, and (c) lightning flash density reported by the GLD360 for 2013-2017.

Their research has shown the existence of two categories of TGFs − those accompanied by nearly simultaneous EMPs that last for roughly a ten-thousandth of one second, and those without simultaneous EMPs. The team researched the dependence of the TGF-associated EMP-peak-amplitude on the horizontal distance between the Fermi spacecraft and the TGF source. They found independent evidence that the EMPs and TGFs are produced by the same phenomenon, rather than the EMPs being from “regular” lightning in TGF-producing thunderstorms.

“We are confirming that these electromagnetic pulses are actually the signatures of the TGFs themselves, which is important for further understanding the physics of these discharges. The ongoing modeling work in this area will be tested by its ability to reproduce the measured TGF-signatures in different frequency ranges,” Nag said.

During the research, the team also discovered that the EMPs produced by TGFs have an average peak value that is two to three times larger than “regular” cloud-to-ground lightning discharges. Initial data suggest that TGFs don’t happen with every thunderstorm, though advancements in detection technology may provide new information on their occurrence characteristics in the future.

While the energetic radiation from TGFs can reach the ground, previous research has shown that these flashes are more often detected by space-based detectors. It is currently unknown how the radiation doses and EMPs from gamma ray flashes can affect aviation activities, tall ground-based structures such as cell towers, and places at high elevation. However, the team is looking to analyze these impacts further.

Future research includes looking at deploying an array of ground-based energetic-radiation detectors and field measurements in order to get more information on the physics and effects of TGFs.

“In the paper, we call them ‘enigmatic’ because they have these unique facets we are learning more about,” Nag said. “In order to gain a better understanding of this phenomenon, observations are key, followed by analysis and modeling.”

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