Scientists Discovered Phenomenon Impacting Earth's Radiation Belts

Two scientists from the University of Alaska Fairbanks, Vikas Sonwalkar and Amani Reddy, uncovered a new form of "whistler." This electromagnetic wave carries significant lightning energy to Earth's magnetosphere. Their findings appear in Science Advances.

Sonwalkar, a professor emeritus, and Reddy, an assistant professor, identified this wave type. It transports lightning energy, entering the ionosphere at low latitudes, then reflects upward at approximately 55 miles altitude into the opposite hemisphere.

Previously, it was thought that lightning energy entering low latitudes remained in the ionosphere and did not reach the radiation belts. These belts consist of two layers of charged particles surrounding Earth, maintained by its magnetic field.

Sonwalkar emphasized society's dependence on space technology. "Modern communication and navigation systems, satellites, and astronauts are at risk from harmful energetic particles in the radiation belts," he noted. These particles can damage electronics and pose health risks, including cancer.

Understanding radiation belts and the electromagnetic waves affecting them, especially from terrestrial lightning, is essential for safe human operations in space. Sonwalkar and Reddy describe the newly discovered wave as a "specularly reflected whistler." Whistlers produce a whistling sound when played through speakers. In contrast, lightning energy entering at higher latitudes creates a different type known as magnetospherically reflected whistlers, reflecting multiple times within the magnetosphere.

The ionosphere is a part of Earth's upper atmosphere, containing high concentrations of ions and free electrons. It is ionized by solar radiation and cosmic rays, crucial for radio communication as it modifies and reflects radio waves.

Earth's magnetosphere, created by the planet's magnetic field, surrounds it and serves as a protective barrier. This area prevents most particles from the solar wind from damaging the atmosphere and life. Sonwalkar and Reddy's research establishes that both types of whistlers—specularly and magnetospherically reflected—coexist in the magnetosphere.

Their study utilized plasma wave data from NASA's Van Allen Probes, which operated from 2012 until 2019, along with lightning information from the World Wide Lightning Detection Network. They created a wave propagation model. This model revealed the doubled energy of lightning reaching the magnetosphere when accounting for specularly reflected whistlers.

Analysis of Van Allen Probes data demonstrated that specularly reflected whistlers are prevalent in the magnetosphere. Most lightning strikes occur in low latitudes, particularly in tropical and subtropical areas that experience regular thunderstorms.

Sonwalkar stated, "This suggests that specularly reflected whistlers likely convey a greater portion of lightning energy to the magnetosphere than their magnetospherically reflected counterparts." Since the 1950s, researchers have explored the effects of lightning-generated whistler waves on radiation belt physics and their potential for remote sensing of magnetospheric plasma.

Both Sonwalkar and Reddy are part of the Department of Electrical and Computer Engineering in UAF's College of Engineering and Mines. Reddy also has ties with the UAF Geophysical Institute. Their research is made possible through grants from the National Science Foundation and NASA EPSCoR, which stands for the Established Program to Stimulate Competitive Research.

Earlier SSP wrote about the new insights into the aging immune system.