Dear MEL Topic Readers,
'It sounded kind of crazy': How ripples in the high atmosphere warned
scientists of a tsunami in real time
GPS satellites orbit at an altitude of approximately 20,000 km above the
Earth’s surface. Below them, there is a layer of atmosphere that extends from
about 80 to 1,000 km above the Earth’s surface, called the ionosphere, which
contains ions and free electrons. When a significant shock wave occurs caused
by a mega earthquake, volcanic eruption, rocket launch, or underground nuclear weapon
test, it displaces a large amount of air, sending low-frequency sound and
gravity waves upward into the atmosphere. This interacts with the particles in
the ionosphere and causes slight distortions in the radio signals transmitted
from GPS satellites to ground stations. Such distortions were recorded by the 2011
massive earthquake in Japan and the 2022 volcanic eruption in Tonga. NASA’s real-time
disaster information and alert system, GUARDIAN, analyzes such distortions, identifies
the causes, and then issues an alert accordingly. Along with the DART tsunami
detection system that uses buoys moored to the ocean floor, NASA’s GUARDIAN
could warn people in coastal communities of a tsunami before its arrival.
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