Earth’s Magnetic Song Recorded for the First Time During a Solar Storm

In quiet times, when no solar storm is striking the Earth, the song is lower in pitch and less complex, with one single frequency dominating the oscillation. When a solar storm hits, the frequency of the wave is roughly doubled, with the precise frequency of the resulting waves being dependent on the strength of the magnetic field in the storm.

“It’s like the storm is changing the tuning of the foreshock,” Turc said.

And it doesn’t stop there. Not only does the frequency of the wave change but it also becomes much more complicated than the single frequency present in quiet times. Once the storm hits the foreshock, the wave breaks into a complex network of different, higher frequencies.

Computer simulations of the foreshock, performed using a model called Vlasiator, which is being developed at the University of Helsinki, demonstrate the intricate wave pattern that appears during solar storms.

The changes in the foreshock have the power to affect the way the solar storm is propagated down to the Earth’s surface. Although it is still an open question exactly how this process works, it is clear that the energy generated by waves in the foreshock cannot escape back into space, as the waves are pushed towards Earth by the incoming solar storm.

Before they reach our atmosphere, however, the waves encounter another barrier, the bow shock, which is the magnetic region of space that slows down solar wind particles before they collide with Earth’s magnetic field. The collision of the magnetic waves modifies the behavior of the bow shock, possibly changing the way it processes the energy of the incoming solar storm.

Behind the bow shock, the magnetic fields of Earth start to resonate at the frequency of the waves and this contributes to the transmission of the magnetic disturbance all the way to the ground. It is a fast process, taking around 10 minutes from the wave being generated at the foreshock to its energy reaching the ground.

Turc and her colleagues are now working to understand exactly how these complex waves are generated. “We always expected a change in frequency but not the level of complexity in the wave,” she added.

Solar storms are a part of space weather. While the solar wind is always blowing, explosive releases of energy close to the Sun’s surface generate turbulence and gusts that eventually give rise to solar storms.

Understanding space weather has become increasingly important to society because of the damaging effects solar storms can have on sensitive electronics and technology on ground and in space. It is now more important than ever that we understand how space weather disturbances such as solar storms propagate through the Solar System and down to Earth, and ESA’s upcoming Solar Orbiter mission, scheduled for launch in February 2020, will contribute to these investigations.

This new scientific study based on the long-lived Cluster mission provides another detail in that knowledge but it also has a larger role to play in our understanding of the Universe. Magnetic fields are ubiquitous and so the kind of complex interaction seen in Earth’s foreshock may take place in a variety of cosmic environments, including exoplanets orbiting close to their parent star, as they would be immersed in intense magnetic fields.

“This is an excellent example of how Cluster continues to extend our knowledge of the Sun-Earth connection, even years after the original data was obtained,” said Philippe Escoubet, ESA Project Scientist for Cluster. “The results take us deeper into the details of fundamental magnetic interactions that take place across the Universe.”

Contacts and sources:
Nanci Bompey. American Geophysical Union
Claudia Mignone, European Space Agency
Lucile Turc, University of Helsinki, Finland
Philippe Escoubet, European Space Agency

Citation: “First observations of the disruption of the Earth’s foreshock wave field during magnetic clouds”

L. Turc: Department of Physics, University of Helsinki, Finland;

O. W. Roberts: Space Research Institute, Austrian Academy of Sciences, Austria; and Directorate of Science, European Space Research and Technology Centre (ESA/ESTEC), The Netherlands;

M. O. Archer: School of Physics and Astronomy, Queen Mary University of London, United Kingdom;

M. Palmroth: Department of Physics, University of Helsinki, Finland; and Finnish Meteorological Institute, Helsinki, Finland;

M. Battarbee, T. Brito, U. Ganse, M. Grandin, Y. Pfau-Kempf: Department of Physics, University of Helsinki, Finland;

C. P. Escoubet: Directorate of Science, European Space Research and Technology Centre (ESA/ESTEC), The Netherlands;

I. Dandouras: IRAP, Universit´e de Toulouse / CNRS / UPS / CNES, France.