On April 8, 2024, a total solar eclipse will occur in parts of the United States, and NASA-funded experiments are set to investigate the effects of this celestial event on the ionosphere. While millions of people along the path of totality will experience a temporary darkness and changes in temperature and wind patterns, the impact on the ionosphere is far more significant. The ionosphere, an electrically conductive layer of the atmosphere located 100 to 400 miles above the Earth’s surface, undergoes amplified changes during a solar eclipse.
The ionosphere plays a crucial role in long-distance AM and shortwave radio communication. Radio operators utilize this layer by bouncing signals off it, allowing broadcasts to reach hundreds or even thousands of miles. The ionosphere is sustained by the Sun, as its rays separate negatively charged electrons from atoms, creating positively charged ions. At night, the ionosphere undergoes recombination, causing over 60 miles of it to disappear. When dawn breaks, the electrons are freed again, and the ionosphere expands due to the Sun’s illumination. This daily cycle is known as the “breathing” of the ionosphere.
A total solar eclipse presents a unique opportunity for scientific observation. Three NASA-funded projects are focusing on studying the changes that occur during an eclipse. One of these projects is the Super Dual Auroral Radar Network (SuperDARN), which consists of radars positioned around the world. These radars bounce radio waves off the ionosphere and analyze the returning signal to determine changes in density, temperature, and movement. During the 2024 eclipse, three U.S.-based SuperDARN radars will be observing the ionosphere’s response to the eclipse’s solar radiation changes. Bharat Kunduri, a professor at Virginia Polytechnic Institute and State University, leads a team that will compare SuperDARN’s measurements with computer models to gain insights into how the ionosphere reacts during a solar eclipse.
Another experiment, the Ham Radio Science Citizen Investigation (HamSCI), involves amateur radio operators or “ham” radio operators. These operators will attempt to send and receive signals to one another before, during, and after the eclipse. Nathaniel Frissell, a professor at the University of Scranton, leads the HamSCI project. The goal is to understand how the sudden loss of sunlight during totality affects radio signals. Previous experiments conducted during the 2017 total solar eclipse and the 2023 annular eclipse showed that the ionosphere behaved similarly to nighttime conditions. Signals traveled farther, and frequencies typically used at night became usable. Frissell aims to continue comparing eclipses and the day/night cycle to assess the widespread changes in the ionosphere and compare the results with computer models.
The final experiment, called RadioJOVE, focuses on documenting radio signals from space, particularly those from Jupiter. During the 2024 total solar eclipse, RadioJOVE participants will shift their attention to the Sun. Using self-assembled radio antenna kits, they will record solar radio bursts before, during, and after the eclipse. In the 2017 eclipse, some participants observed a decrease in the intensity of solar radio bursts. However, further observations are needed to draw definitive conclusions. Chuck Higgins, a professor at Middle Tennessee State University and founding member of RadioJOVE, hopes that with better training and more observers, they can gather more data to study radio propagation through the ionosphere.
These NASA-funded experiments provide valuable opportunities to study the effects of a total solar eclipse on the ionosphere. By analyzing data from radars, amateur radio operators, and citizen scientists, researchers aim to understand how the ionosphere responds to changes in solar radiation. The findings will contribute to our understanding of this enigmatic layer of the atmosphere and its impact on long-distance radio communication. As the 2024 eclipse approaches, scientists and enthusiasts eagerly await the chance to witness this natural experiment in action and uncover new insights about our atmosphere.