Two scientists at the University of Alaska Fairbanks have discovered a new type of “whistle,” an electromagnetic wave that carries significant amounts of lightning energy into the Earth’s magnetosphere. The study was published on: Science Developments. Professor Emeritus Vikas Sonwalkar and Associate Professor Amani Reddy discovered a new type of wave. The wave carries the energy of lightning entering the ionosphere from lower latitudes to the magnetosphere. The energy is reflected upwards by the lower boundary of the ionosphere at an altitude of about 55 miles in the opposite hemisphere.

The authors previously believed that lightning energy entering the ionosphere at low latitudes was trapped in the ionosphere and therefore did not reach the radiation belts. The belts are two layers of charged particles that surround the planet and are held in place by the Earth’s magnetic field.

“As a society, we are dependent on space technology,” Sonwalkar said. “Modern communication and navigation systems, satellites and spacecraft carrying astronauts come into contact with harmful energetic particles from the radiation belts, which can damage electronics and cause cancer. “A better understanding of the radiation belts and the various electromagnetic waves that affect them, including Earth’s lightning, is vital to human space activities,” he said.

Sonwalkar and Reddy’s discovery is a type of hiss wave they call “reflected hiss.” Whistlers make a whistling sound when played through a loudspeaker.

Lightning energy entering the ionosphere at higher latitudes reaches the magnetosphere as another type of whistle, called a magnetospherically reflected whistle, which undergoes one or more reflections in the magnetosphere.

The ionosphere is a layer of the Earth’s upper atmosphere characterized by a high concentration of ions and free electrons. It is ionized by solar radiation and cosmic rays, making it conductive and important for radio communications as it reflects and modifies radio waves.

Earth’s magnetosphere is the region of space surrounding the planet and created by Earth’s magnetic field. It forms a protective barrier that prevents most solar wind particles from entering the atmosphere and harming life and technology.

Sonwalkar and Reddy’s work shows that both types of whistles (specularly reflected whistles and magnetospherically reflected whistles) coexist in the magnetosphere.

In their study, the authors used plasma wave data from NASA’s Van Allen Probes, which were launched in 2012 and operated until 2019, and lightning data from the Worldwide Lightning Detection Network.

They developed a wave propagation model that showed that by looking at specular whistles, the lightning energy reaching the magnetosphere doubles. Analysis of plasma wave data from the Van Allen Probes revealed that specular whistles are a common phenomenon in the magnetosphere. Most lightning occurs at low latitudes, in tropical and subtropical regions where thunderstorms tend to develop.

“This means that specularly reflected whistles likely transport more lightning energy into the magnetosphere compared to magnetospherically reflected whistles,” Sonwalkar said.

The effects of lightning-generated whistler waves on the physics of the radiation belt and their use in remote sensing of magnetospheric plasma have been studied since the 1950s. Sonwalkar and Reddy are in the Department of Electrical and Computer Engineering in the UAF College of Mining Engineering. Reddy is also affiliated with the UAF Geophysical Institute. Sonwalkar and Reddy’s research is supported by grants from the National Science Foundation and NASA’s EPSCoR, a well-established competitive research incentive program.