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Tokyo academics develop tsunami-predicting system using airborne electron density

TOKYO -- University academics here have developed a system that can predict the scale and arrival time of a tsunami based on electron density changes in the sky.

Under the system, associate professor Masashi Kamogawa of Tokyo Gakugei University expects to make predictions based on a phenomenon known as "ionospheric holes" -- whereby electron density roughly 300 kilometers in the air becomes lower upon the occurrence of a tsunami.

The new method, combined with observations using seismometers and tsunami gauges, is expected to enable more precise tsunami predictions, according to a research team led by Kamogawa.

Analyzing archived GPS radio wave data, the team noticed ionospheric holes directly above the epicenter of tsunami generated by the Great East Japan Earthquake in March 2011.

The reason behind the phenomenon relates to air vibrations caused by a surge on the ocean surface.

During the analysis, the team worked with the phenomenon of the GPS radio wave frequency being disrupted when the signals passed through ionospheric holes.

They examined data from seven GPS satellites as well as about 1,000 receivers in Japan on seven Pacific Ocean tsunamis over the past 20 years. The seven tsunamis include one triggered by an earthquake in 2004 off the coast of Sumatra.

The team then developed a program that can calculate the scale of tsunami by estimating the size of ionospheric holes based on the extent of GPS radio wave frequency disruptions, among other data.

Moreover, to enhance the accuracy of the system, as early as next month the team is set to conduct a simulation based on tsunami expected to be generated by a powerful Nankai Trough earthquake. The simulation will be derived from a tsunami impact model for Chubu Electric Power Co.'s Hamaoka Nuclear Power plant.

It takes at least eight minutes for an ionospheric hole to form after the onset of a tsunami. However, if all goes well, Kamogawa says his method will be more precise, and quicker at predicting imminent tsunami than using seismometers or tsunami gauges on the ocean floor, depending on their scale or distance from land.

Kamogawa explains that the GPS method will allow developing countries that do not have enough tsunami gauges to easily predict the scale and arrival time of tsunami.

Tohoku University tsunami engineering professor Fumihiko Imamura told the Mainichi Shimbun, "If the new system can be established, it will possible to see the full picture concerning an approaching tsunami, and hence make more precise predictions."

(Japanese original by Suzuko Araki, Science and Environment News Department)

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