How ripples in the high atmosphere warned scientists of a tsunami in real time

The reason why navigation satellite signals can register a tsunami is because of the up-and-down motion of the sea. When a tsunami begins to form in the open ocean, its waves may not be very high – perhaps between 10-50cm (4-20 inches). “It’s almost invisible while it’s travelling in the open ocean,” says Yue Cynthia Wu, a researcher in marine engineering at the University of Michigan who specialises in ocean wave dynamics.

This undulation, however, occurs on a gigantic scale, moving extremely large amounts of water at once. This movement displaces the air above it, which disturbs the atmosphere higher up, creating ripples in the layer of charged particles that form the ionosphere some 30 to 190 miles above the Earth’s surface. The ripples alter the number of electrons present in parts of the ionosphere.

“You have ionic reactions, you change the temperatures, it gets out of whack,” says Michael Hickey, professor emeritus of physics at Embry-Riddle Aeronautical University, in Daytona Beach, Florida, who has studied these atmospheric waves.

Navigation satellites use dual frequencies to communicate with ground stations on Earth, so increases in the number of electrons in the ionosphere can cause unusual delays in the time it takes for these two signals to arrive. By measuring those delays, systems such as Guardian can detect whether something weird is going on in the ionosphere.