As a tsunami travels through the ocean, it scoops up a curtain of air known as an internal gravity wave. The wave of air travels upward, eventually reaching the boundary between Earth’s upper atmosphere and the vacuum of space.
Here, in a region called the ionosphere, the gravity wave bumps into free electrons. By analyzing the effects of the motion of these electrons using GPS receiver networks and specially designed ionospheric imaging systems, researchers can track the progress of tsunamis.
Research in this field won graduate student Matt Grawe (BSEE ’15) the National Science Foundation-sponsored CEDAR (Coupling, Energetics, and Dynamics of Atmospheric Regions) poster workshop in Seattle. He conducted the research as an undergraduate.
Grawe’s research focused on understanding how measurements of the ionosphere made by GPS receiver networks and ionospheric imaging systems change when the ionosphere is perturbed by a gravity wave launched by a tsunami.
By understanding the relationship between the properties of the tsunami and its ionospheric signature, scientists may one day be able to augment the current tsunami warning system, which is based on ocean buoys and seismographs, with upper atmospheric remote sensing techniques.
The method is still far from perfect, however, and Grawe’s contributions were to clarify the technique for further use. One flaw in the method is that, for various reasons, the strength of the tsunami doesn’t always line up with how much it affects the ionosphere.
“There are two tsunamis we used to compare the method: the 2011 Tohoku tsunami from Japan, and the 2012 Haida Gwaii tsunami from British Columbia,” Grawe said. “The Tohoku earthquake resulted in a much stronger tsunami, so one might expect stronger perturbations in the ionosphere. But our measurements indicated that the weaker Haida Gwaii tsunami from Canada actually produced a stronger signature in the ionosphere. My research was based on trying to find out why these didn’t match up.”
An uninformed researcher looking at the data might expect a stronger tsunami to disturb more electrons. To make the method more useful, Grawe needed to account for why the weaker tsunami had a greater effect on the ionosphere.
One effect: the direction the tsunami travels relative to the Earth’s magnetic field changes how hard it is for the internal gravity wave to move electrons in the ionosphere. The stronger Tohoku earthquake generated a powerful tsunami, but the weaker Haida Gwaii tsunami was more closely aligned with the Earth’s magnetic field as it propagated, which made it easier for its internal gravity wave to move more electrons.
“The main benefit of looking into this is that it opens up avenues for tsunami detection and warning,” Grawe said. “If we can better understand the physical process, starting from the sea surface variation and ending with our measurements of total electron content and airglow, it may be possible to track tsunamis with a single geostationary satellite that covers an entire ocean.”
This work constituted the basis for Grawe’s senior thesis, which he condensed into a poster for CEDAR.
“At the actual poster competition, judges come up and look at your poster, ask you questions about it, trying to find caveats and things you can improve,” Grawe said. “I was surprised afterward to find out I’d won.”
Since then, Grawe has first-authored a paper on the research. The paper was recently accepted to Earth and Space Science, a journal published by the American Geophysical Union (AGU).
Grawe credits his performance with great fascination and dedication to the work with which he’s involved. His interest in the subject area combined with its life-saving potential motivated him to give his best efforts, both in doing research and in presenting his work.
Grawe’s adviser, Professor Jonathan Makela, was full of praise for his efforts, and his performance as an undergraduate student.
“Matt was taking my GPS course two years ago, and came to talk to me about getting involved in some research,” Makela said. “Matt is driven and bright, and after we first sat down and discussed a few things he was immediately able to get started on the work. I could tell he was interested in this not just from a science standpoint, but also for its potential for augmenting the tsunami warning system and making a positive social impact.”