Solar eclipses don’t just look cool – they can send gravity waves rippling through Earth’s atmosphere like dropping a stone in a pond. An international team of students has measured these gravity waves for the first time.
Gravity waves are a common occurrence in the atmosphere. They can be triggered when pockets of air are pushed upwards, then will naturally sink, but gain heat as they do and start to rise again. This creates a familiar wave pattern that can be seen in radar images and even sometimes from the ground, as clouds gather on the peaks and clear air remains in the troughs.
Side note: these gravity waves aren’t to be confused with gravitational waves. The latter are ripples in the literal fabric of spacetime itself, created by cosmic cataclysms like black holes colliding.
Triggers for gravity waves can be things like mountain ranges, storm cells, and even just the difference in temperature between day and night. As such, it was long predicted that solar eclipses should have a similar effect on the atmosphere. The Nationwide Eclipse Ballooning Project (NEBP) was designed to find out.
Supported by NASA and the National Science Foundation, NEBP involves teams of students from various universities sending weather balloons into the skies during eclipses. Each one carried an instrument package called a radiosonde, which measures temperature, location, humidity, wind direction and wind speed. All of these markers are recorded every second of the flight, with the data transmitted to teams on the ground and eventually uploaded to a central server for analysis.
The NEBP first conducted these experiments during total eclipses in 2019 and 2020, but both events were inconclusive – the first time, because balloons were launched hourly from just one site, while the second was overcome with heavy rains.
So for the 2023 and 2024 eclipses, the project was more prepared. Across the two events, 34 teams launched balloons every 15 minutes for a day before the eclipse, from various sites within the path of totality. Sites were also chosen that had conditions that wouldn’t normally generate gravity waves – so calm weather systems and no nearby mountains.
Among the findings, one team at Fort Wayne, Indiana saw their balloon drop from 85,000 to 65,000 ft (25,900 to 19,800 m) during the eclipse. But this flood of data also revealed the telltale signature of atmospheric gravity waves.
“We put all the data together according to time, and when we plotted that time series, I could already see the stripes in the signal,” said Jie Gong, co-investigator of the research. “I bombarded everybody’s email. We were quite excited.”
The preliminary results, which were presented at the summer meeting of the American Astronomical Society, can be accessed online. A 360-degree video from cameras on one balloon during the eclipse can be seen below.
Sources: NASA, Montana State University