This summer's Great American Eclipse was a historic moment for those who were lucky enough to witness it, but for scientists, it also marked the moment when the almost five-decade-old "bow-wave theory" was proven.
In a study published earlier this week in the journal Geophysical Research Letters, scientists from the Massachusetts Institute of Technology's Haystack Observatory and Norway's University of Tromso presented the "first unambiguous evidence" of bow waves in Earth's upper atmosphere, or ionosphere, in the aftermath of an eclipse. According to Science Alert, the researchers made use of sensors from about 2,000 sites across the United States to conclude that the waves were seen in the August 2017 total solar eclipse, close to 50 years after it was first theorized that solar eclipses could create rippling waves in the ionosphere.
The bow-wave theory was first proposed in 1970, as researchers hypothesized that when solar eclipses take place, the moon's shadow drops onto the atmosphere and quickly moves across our planet, with temperatures dropping at a similarly rapid rate. As Science Alert explained, this phenomenon results in gravity waves appearing in the upper atmosphere, with their rippling nature similar to how ships create waves as they sail across the ocean.
Several studies followed the original paper from 1970, all hoping to prove the bow-wave theory correct. These included studies from 1973, 1976, and 1987 that detailed findings which suggested the creation of bow waves in the wake of a solar eclipse, but ultimately failed to provide any solid form of corroboration.
A 2011 study from Taiwan showed more promise, as researchers announced that they used ground-based GPS satellite receivers to monitor an eclipse from two years prior and search for changes in electron content. As gravity waves are distinguished by higher plasma concentration in the ionosphere, higher electron counts were thought of as a sign that the bow-wave theory would have been playing out at the time of the eclipse.
When analyzing this year's Great American Eclipse, the MIT and Tromso researchers used the same technique, but had the advantage of having much more land that they could track the shadow with. Together with the greater concentration of sensors, this meant the researchers had substantially more data to work with, and a better chance of proving the bow-wave theory to be correct."We were looking at some phenomena that were expected but never had the chance to be observed," said study author and MIT Haystack Observatory researcher Shun-Rong Zhang in an interview with Gizmodo.
"That was the surprise we found... we had a large coverage and our system is sensitive enough to be able to see these smaller variations. That was really very interesting to us."Zhang further explained that the atmospheric changes brought about by bow waves are nothing to worry about, unlike the solar storms that could wreak havoc on communications systems and electrical grids. As the atmosphere has regions with neutral particles just as it has regions with charged particles, scientists are constantly studying the ways in which these regions interact with each other, with the newly-established proof of the bow-wave theory "[furthering] our understanding of that interconnectedness," according to Gizmodo.