Sensors from 2,000 sites across the US have enabled scientists to prove the often hypothesized phenomenon of "bow waves." Researchers have what they are claiming is the "first unambiguous evidence" of upper atmospheric bow waves in the wake of an eclipse.
The detection was the result of a collaboration between MIT's Haystack Observatory and Norway's University of Tromsø.
The Great American Eclipse afforded an opportunity to conduct scientific research using equipment based in America. The hypothesis that a solar eclipse would produce bow waves in the upper atmosphere was proposed in 1970. According to this idea, as the Moon's shadow is falling onto the atmosphere and moving across the planet with supersonic speed, the temperature dramatically falls.
This rapidly moving shadow causes gravity waves in the upper atmosphere. Since the initial proposal in 1970, several attempts have been made to observe these waves. For starters, a 1973 study was inconclusive.
In a 1976 eclipse in Australia, Microbarographs were used to observe and that study produced findings that were consistent with the eclipse bow wave hypothesis. Then, data consistent with eclipse bow waves were observed in 1987 - but neither of these events produced conclusive results.
The waves were announced to have been observed in 2011 by researchers from Taiwan using ground-based GPS satellite receivers to track a 2009 eclipse over Taiwan and Japan, looking for changes in electron content - a higher electron count means a higher level of ionization as electrons get stripped from atoms, creating a plasma. Gravity waves are essentially a higher concentration of plasma in the ionosphere and can be ascertained by that spike in electron content.
The researchers observed both bow and stern waves, wavelengths between 36 and 120 kilometres (22 and 75 miles), periods of three or five minutes, and travelling through the ionosphere at 100 metres (330 feet) per second.
The waves were observed as electron changes across central and eastern US, with 300-400 kilometre wavelength, periods of around 25 minutes, and traveling at speeds of 280 metres per second - too quickly to be attributed to known gravity wave disturbances we get due to typical ionospheric processes.
"This study reveals complex interconnections between the Sun, Moon, and Earth's neutral atmosphere and ionosphere, and demonstrates persistent coupling processes between different components of the Earth's atmosphere, a topic of significant community interest," the researchers wrote in their paper.