Discovery of electromagnetic wave reveals new phenomenon affecting Earth’s radiation belts

Researchers at the University of Alaska Fairbanks identified a new electromagnetic wave called the “specularly reflected whistler.” This wave, caused by low-latitude lightning, challenged earlier notions by revealing that lightning energy can escape the ionosphere and enter the magnetosphere, impacting space weather dynamics.

• The study found specularly reflected whistlers as an important mechanism for delivering lightning energy from the ionosphere to the magnetosphere, changing our knowledge of lightning’s effect on the Earth’s magnetic field.
• The study, done by Vikas Sonwalkar and Amani Reddy at the University of Alaska Fairbanks, was published in August 2024 and focused on low-latitude regions such as Brazil and India, using data collected from 2021 to 2023.

The discovery of the “specularly reflected whistler” which is an electromagnetic wave was made by Vikas Sonwalkar, professor emeritus, and Amani Reddy, assistant professor at the University of Alaska Fairbanks (UAF). Their research was supported by the National Science Foundation and NASA EPSCoR. Researchers from NASA and the World Wide Lightning Detection Network also made significant contributions, providing critical data for the study.

“We report the discovery of specularly reflected (SR) whistler in which the lightning energy injected into the ionosphere at low latitudes reaches the magnetosphere after undergoing a specular reflection in the conjugate ionosphere, contradicting previous claims that lightning energy injected at low latitudes cannot escape the ionosphere. SR whistlers provide a low-latitude channel to transport lightning energy to the magnetosphere,” the researchers stated.

Identifying the SR Whistler is important for understanding how lightning energy moves from the ionosphere to the magnetosphere. Unlike previously reported waves, specularly reflected whistlers originate at low latitudes and reflect off the ionosphere’s lower boundary, transporting lightning energy to the magnetosphere.

This study called into question the long-held belief that lightning energy is limited to the ionosphere and revealed a more intricate interplay between lightning energy and the Earth’s magnetic field.

The study focused on low-latitude locations, particularly those around the Earth’s equator, where lightning and the magnetosphere interact the most. Data for this study were collected from a variety of tropical sites, including Brazil and India, using satellite observations and ground-based sensors.

The findings were published in August 2024, after years of data collection and analysis from 2021 to 2023. This extended timescale enabled researchers to collect substantial data on whistler waves and their interactions with the magnetosphere under a variety of geomagnetic conditions.

Identifying specularly reflected whistlers is important for advancing our understanding of space weather and its effects on technology. Lightning discharges emit significant energy into the magnetosphere, disrupting satellite communications, GPS systems, and power grids. This study attempted to improve space weather forecasting and protect technological infrastructure from disturbances caused by lightning energy entering the magnetosphere.

The researchers used historical plasma wave data from NASA’s Van Allen Probes and lightning data from the World Wide Lightning Detection Network. Researchers created a wave propagation model that included specularly reflected whistlers, demonstrating a doubling of lightning energy reaching the magnetosphere above previously known processes. This model explained how specularly reflected whistlers, which reflect upward from the ionosphere’s lower limit, carry a considerable amount of lightning energy to the magnetosphere.

“We conclude that SR whistler is a common magnetospheric phenomenon that carries a substantial portion of the lightning energy reaching the magnetosphere and arguably plays an important role in the physics of the radiation belts. The dispersion of SR and MR whistlers coupled with ray tracing simulations provide a method for obtaining 2D images of magnetospheric plasma density and composition. The intensities of SR and MR whistlers coupled with the whistler propagation model provide new methods of measuring E-I waveguide and transionospheric losses and remote sensing of lightning flash location and intensity,” the researchers concluded.

References: 

¹ Specularly reflected whistler: A low-latitude channel to couple lightning energy to the magnetosphere – Vikas S. Sonwalkar, Amani Reddy – Sci. Adv.10,eado2657(2024) – August 16, 2024 – https://doi.org/10.1126/sciadv.ado2657 – OPEN ACCESS

Harsha Borah

Harsha Borah is an experienced content writer with a proven track record in the industry. Harsha has worked with LitSpark Solutions and Whateveryourdose, honing skills in creating engaging content across various platforms. A gold medalist in a state-level writing competition organized by Assam Tourism, Harsha’s travelogue on Tezpur was widely appreciated. Harsha’s article, "The Dark Tale of the Only Judge in India to Be Hanged," ranks second on Google and has garnered over 11 000 views and 8 900 reads on Medium. Outside of writing, Harsha enjoys reading books and solving jigsaw puzzles.

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