When a solar storm hits the Earth not only do we see aurora, but the planet hums an eerie tune. The unusual song resembles the chipping of birds mixed with a the swirling, burbling sounds of electrons dancing in magnetic fields. New data from European Space Agency’s Cluster mission reveals that the song comes from waves generated in Earth’s magnetic field when a storm of electrically-charge particles from the sun slams into it.
Cluster consists of four spacecraft that orbit Earth in formation and investigate our planet’s magnetic environment and its interaction with the solar wind, a constant supersonic flow of electrons and protons from the sun. Picture steam rising from a hot potato after plucking it from boiling water except that the “steam” is moving at hundreds of miles a second and directed outward toward the planets.
The Earth’s magnetic field is an obstacle to the sun’s exhalations. The material piles in front of it to form a bow shock, similar to the way a moving boat piles water ahead of itself into a bow wave. Just ahead of the bow shock is the foreshock region. During part of their orbit the four Cluster spacecraft repeatedly fly through the foreshock just ahead of the bow shock. From 2001 to 2005, the spacecraft flew through six collisions between solar storms and Earth’s magnetic field and recorded the waves that were generated.
Hear Earth’s magnetic field sing! The first sound file was made during quiet times, the second when a solar storm hit. The difference is amazing.
During collisions, the foreshock encounters release magnetic waves that can be transformed into audible sound that resemble a special effect straight out of a sci-fi movie. In quiet times, when the solar winds are relatively calm, the song is lower in pitch and less complex, with one single frequency dominating. When a solar storm hits, the frequency of the waves is roughly doubled and much more complicated. In a word — lively! Click on the video or the individual links to hear it.
Energy generated by waves in the foreshock don’t escape back into space but are pushed towards Earth by the incoming solar storm. Before they reach the atmosphere they plow into the bow shock which slows the particles down before they collide directly with Earth’s magnetic field. Meanwhile, behind the bow shock, the magnetic fields of Earth start to resonate at the frequency of the waves and conduct the magnetic disturbance all the way to the ground. It’s a fast process, taking around ten minutes from the time the wave forms at the foreshock to its energy reaching the ground. I wish I had the ears to hear it!
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. These effect Earth in many ways from producing auroral eye-candy to damaging satellite electronics. They also work in concert with our planet’s own magnetic field to compose an Earth-song that expands our sense of cosmic wonder.
For more information, you have free access to the scientific paper on the topic.