Tsunamis which often cause huge destruction on land also make a surprising impression even 300 km high above the Earth, scientists say.
According to researchers, tsunamis generate mysterious “atmospheric gravity waves” and their better understanding would help gather better data on the potentially devastating ocean-based waves and improve tsunami warning networks.
“The tsunami very effectively generates atmospheric gravity waves, and because they’re fast, those waves can effectively travel to the upper atmosphere,” said Michael Hickey, a physics professor and associate dean at Embry-Riddle Aeronautical University in Florida.
Hickey, who works on computer modelling, has teamed up with researchers who are using GPS to observe these waves in ionosphere, an area in the atmosphere which lies between 50 and 300 miles (80 and 500 km) above the Earth.
Essentially, like an uninvited guest at a party, these tsunami-generated waves go barging into parts of the ionosphere where they’re not generally seen, causing a ruckus among the particles that live there, he said.
The waves, he added, cause anomalies in GPS data, and may allow scientists someday to better pinpoint the origin and magnitude of a tsunami, LiveScience reported.
“We’re not at that stage yet,” Hickey cautioned, but said that eventually, “an early warning system is the goal“.
According to scientists, tsunami sky waves are a grand affair. The waves can travel higher than 300km above the Earth — equivalent to a trip from Chicago to Indianapolis. Their peaks and valleys are sometimes hundreds of meters apart; their horizontal wavelengths — the distance from one peak to the next — can be several hundred kilometres.
But when these waves start off, they are tiny. The force of a tsunami will disturb the air at the ocean’s surface by just 3-4cm, said David Galvan of NASA’s Jet Propulsion Laboratory in Pasadena. As the atmospheric waves travel upward, they get larger.
“Because the atmosphere decreases in density as you go up, the air molecules can move much farther without bumping into each other,” Galvan explained, adding that as the wave travels through thinner and thinner material, the larger its oscillations can get.
The energy produced by an underwater earthquake or sub-sea landslide is immense, but the disturbance is barely perceptible on the surface of the open ocean because of the vast amount of water through which the energy travels.
However, as that energy approaches the shoreline, there’s less and less water to carry the energy, and the wave becomes huge, said Galvan, who is one of the scientists carrying out observational studies with GPS to track the atmospheric waves.
According to him, scientists have now established that these waves are indeed produced by tsunamis, there’s much work to be done in interpreting how to use the atmospheric data to track down the dangerous waves in the ocean.
Galvan said: “These atmospheric gravity waves are kind of capricious. They appear in some places and not others, and we don’t understand why at this point.”
Galvan, Hickey and colleagues have just submitted a paper for review that examines this question.