Two researchers have made a groundbreaking discovery related to a new form of ‘whistler,’ which is an electromagnetic wave that transports a significant amount of energy from lightning into the Earth’s magnetosphere.
Researchers at the University of Alaska Fairbanks have identified a novel type of “whistler,” an electromagnetic wave capable of transferring considerable lightning energy into the magnetosphere of Earth.
The findings are detailed in the journal Science Advances.
Vikas Sonwalkar, an emeritus professor, and Amani Reddy, an assistant professor, made this discovery. This new wave transfers lightning energy, which enters the ionosphere at lower latitudes, up to the magnetosphere. The ionosphere reflects this energy upward from its lower boundary, located roughly 55 miles above the ground, into the opposite hemisphere.
Prior to this study, the researchers noted, it was generally assumed that lightning energy entering the ionosphere at lower latitudes was confined there and did not reach the radiation belts. These radiation belts are two regions filled with charged particles that envelop the earth, stabilized by the planet’s magnetic field.
“Our technology now heavily relies on space-based systems,” Sonwalkar explained. “Modern communication tools, navigation systems, satellites, and manned spacecraft interact with harmful energetic particles from the radiation belts, which can potentially harm electronics and increase cancer risks.
“Gaining a deeper insight into these radiation belts and understanding the various electromagnetic waves, particularly those produced by terrestrial lightning, is crucial for human activities beyond our planet,” he continued.
The newly identified wave is termed “specularly reflected whistler.” When played through a speaker, whistlers generate a whistling sound.
In contrast, lightning energy entering at higher latitudes creates a different kind known as magnetospherically reflected whistler, which reflects one or more times inside the magnetosphere.
The ionosphere, a section of Earth’s upper atmosphere, is distinguished by a high presence of ions and free electrons. It becomes ionized due to solar radiation and cosmic rays, making it conductive and essential for radio communication, as it helps reflect and alter radio signals.
Earth’s magnetosphere is an area surrounding the planet formed by its magnetic field. It acts as a protective shield, safeguarding the atmosphere and all forms of life by stopping most solar wind particles from penetrating.
The research by Sonwalkar and Reddy illustrates that both specularly reflected whistlers and magnetospherically reflected whistlers exist simultaneously within the magnetosphere.
To conduct their study, the authors utilized plasma wave data from NASA’s Van Allen Probes, which were active from 2012 to 2019, along with lightning data from the World Wide Lightning Detection Network.
They created a wave propagation model that indicated the presence of specularly reflected whistlers leads to a doubling of the lightning energy that manages to reach the magnetosphere.
Analysis of plasma wave data from the Van Allen Probes confirmed that specularly reflected whistlers are frequently observed phenomena within the magnetosphere.
Most lightning strikes occur in low latitude regions, which include tropical and subtropical areas that are particularly likely to experience thunderstorms.
“This suggests that specularly reflected whistlers likely transport a larger share of lightning energy into the magnetosphere compared to magnetospherically reflected whistlers,” Sonwalkar noted.
The influence of lightning-induced whistler waves on the dynamics of radiation belts and their potential application in the remote sensing of magnetospheric plasma has been a topic of study since the 1950s.
