Seismographs sensed the polar lights

(ORDO NEWS) — Scientists have discovered a link between seismograph readings and the intensity of the aurora in Alaska. During the 2019 auroras, which were monitored with magnetometers and all-sky cameras, seismographs simultaneously recorded continuous seismic waves. The revealed regularity can make it possible to significantly expand the system for studying the aurora and the dynamics of the Earth’s magnetic field. The article was published in the journal Seismological Research Letters.

The aurora is the effect of the colorful glow of the upper layers of the atmosphere, which occurs when the solar wind collides with the magnetosphere. Charged particles in the solar wind are redirected and accelerated in the Earth’s magnetic field, reaching the dense layers of the atmosphere in areas close to the magnetic poles. There, they collide with atoms and molecules in the atmosphere and transfer them to an excited state, and in the process of relaxation, the light of the aurora is born.

Often, instead of exciting atoms or molecules, the sun’s rays ionize them, which changes the density of charged particles in the atmosphere and leads to a change in its electrical conductivity. Combined with the electric fields that often occur in the magnetosphere during the aurora, this leads to significant currents in the ionosphere. They, in turn, generate magnetic fields, which are detected by the researchers of the aurora borealis as perturbations of the conditionally stable magnetic field of the Earth using magnetometers.

It is to these fluctuations of the magnetic field that mobile seismographs, which were installed throughout Alaska in 2017, turned out to be sensitive. Mobile seismographs, unlike stationary ones, have no magnetic shielding. Without it, the ferromagnetic components of seismographs are too susceptible to magnetic storms, thereby provoking the registration of waves that in fact have nothing to do with seismic activity.

But a flaw in the design of seismographs has played into the hands of scientists who study the aurora borealis. They are interested in just magnetic fields, but for such studies in Alaska, only 13 magnetometers have been installed against more than 200 seismographs sensitive to oscillations of the Earth’s magnetosphere. In addition, to observe the night sky, scientists use all-sky cameras, but there are only 6 of them installed in Alaska.

Carl Tape of the University of Alaska Fairbanks has demonstrated that magnetic field-sensitive seismographs can serve as a tool for observing the aurora. It turned out that since the installation of the new seismographs, many strong auroras are visible in the seismic data as weak vertical oscillations with a long period of 40–800 seconds. Thus, the aurora that has occurred can be judged by the data not only of magnetometers and cameras of the whole sky, but also by the indices of seismographs; however, the authors have yet to obtain the exact dependence of the data of these instruments.

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Scientists argue that the discovered pattern can help to significantly improve the spatial resolution of observations of the magnetosphere in Alaska. Nevertheless, the authors point to the qualitative approach of their study of the revealed correlation and believe that it is too early to talk about the use of such a technique in real observations.

The work also notes the low accuracy of this approach in comparison with the equipment already in use, so scientists hope to expand the network of magnetometers. This will make it possible not only to improve conditions for studying the magnetosphere, but also to cope with the sensitivity of seismographs to magnetic field fluctuations: if the magnetometer is installed close enough to the seismograph, then from its data it is possible to understand which recorded seismic activity is only a consequence of magnetic action.

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