Atmospheric Airglow Helps Detect Tsunamis

An airglow layer observed in the upper atmosphere that preceded the Japanese tsunami by about one hour has led researchers to consider developing early-warning technology for future tsunamis.

Airglow is a faint greenish radiation layer in the upper atmosphere that results when molecules recombine after being split by sunlight.

The airglow signature was recorded on March 11, located in the ionosphere, 250 kilometers above the Earth’s surface, by researchers at the University of Illinois using a wide-angle camera system located at the top of the Haleakala Volcano in Maui, Hawaii.

As a tsunami travels across the ocean surface, it can create atmospheric gravity waves with the potential to reach several kilometers into the atmosphere, causing oscillations that can be imaged in the airglow layer due to the decrease in air density at that altitude.

“Imaging the response using the airglow is much more difficult because the window of opportunity for making the observations is so narrow, and had never been achieved before,” said researcher Jonathan Makela, at the Coordinated Science Laboratory (CSL), in a press release.

“Our camera happened to be in the right place at the right time.”

The University of Illinois scientists analyzed the images to reveal specific wave periods and orientations, and then researchers in France, Brazil, and the United States cross-checked the results with the tsunami measurements, models, and GPS and satellite data.

“This is a reminder of how interconnected our environment is,” Makela said. “This technique provides a powerful new tool to study the coupling of the ocean and atmosphere and how tsunamis propagate across the open ocean.”

Using this method, the team believes a satellite-based camera system could predict tsunamis in combination with ground-based cameras, GPS receivers, and algorithms to analyze the data.

These findings vindicate a theory from the 1970s, which hypothesized that a tsunami’s signature could be observed in the atmosphere. However, previously this has only been detected using radio signals from satellites.

The study was published in Geophysical Research Letters on July 7.