The discovery of a new type of electromagnetic wave called a “specularly reflected whistler” by University of Alaska Fairbanks scientists Vikas Sonwalkar and Amani Reddy has significant implications for our understanding of energy transfer from lightning to Earth’s magnetosphere. This research, published in Science Advances, reveals that lightning energy entering the ionosphere at low latitudes is reflected upward by the ionosphere’s lower boundary and reaches the magnetosphere, contrary to previous beliefs that this energy remained trapped in the ionosphere. This discovery is important for understanding the radiation belts surrounding Earth, which are crucial for space technology and human operations in space.
Whistler waves, which produce a whistling sound when played through a speaker, play a key role in the transfer of lightning energy to the magnetosphere. Lightning energy entering the ionosphere at higher latitudes reaches the magnetosphere as a different type of whistler known as a magnetospherically reflected whistler, which undergoes multiple reflections within the magnetosphere. The ionosphere, characterized by a high concentration of ions and free electrons, is ionized by solar radiation and cosmic rays, making it essential for radio communication as it reflects and modifies radio waves. Earth’s magnetosphere, created by the planet’s magnetic field, acts as a protective barrier against most of the solar wind’s particles, preventing harm to life and technology.
Sonwalkar and Reddy’s research, based on plasma wave data from NASA’s Van Allen Probes and lightning data from the World Wide Lightning Detection Network, demonstrates the coexistence of both specularly reflected whistlers and magnetospherically reflected whistlers in the magnetosphere. By developing a wave propagation model that considers specularly reflected whistlers, the researchers showed a doubling of lightning energy reaching the magnetosphere, highlighting the significance of this newly discovered type of whistler wave. The review of plasma wave data from the Van Allen Probes revealed that specularly reflected whistlers are a common magnetospheric phenomenon, indicating their importance in energy transfer from lightning to the magnetosphere.
Given that a majority of lightning occurs at low latitudes, which are prone to thunderstorm development, it is likely that specularly reflected whistlers carry a greater proportion of lightning energy to the magnetosphere compared to magnetospherically reflected whistlers. The impact of lightning-generated whistler waves on radiation belt physics and their potential use in remote sensing of magnetospheric plasma has been the subject of research since the 1950s. This new discovery adds to our understanding of how electromagnetic waves originating from terrestrial lightning play a critical role in the dynamics of Earth’s magnetosphere, with implications for space technology and human operations in space.
