A Symphony of Magnetic Waves

Nov. 9, 2021: On Nov. 8th, for only a few hours, Earth’s magnetic field became very quiet. In the silence, a symphony ensued. Citizen scientist Rob Stammes recorded the performance using his magnetometer in Lofoten, Norway. “At first, the line on the digital chart recorder seemed flat,” he says, “but when I zoomed in I saw an almost musical superposition of sine waves.”

“This is very striking,” says Stammes, who has spent years observing and cataloging magnetic disturbances inside the Arctic Circle. “Note how the high-frequency Pc1 and Pc2 waves are superimposed on the slower Pc3. In musical terms, it’s a form of vibrato modulation.”

“Pc” stands for “pulsation continuous.” This is research jargon meaning, essentially, sine waves in the magnetosphere. They are present at all times, usually as a noisy cacophany of competing frequencies. Only during moments of extreme quiet can a few individual frequencies pop out and make music together.

Over the years, researchers have identified 5 types of Pc waves; Stammes recorded 3 of them. Fast Pc1 and Pc2 waves are associated with protons spiralling around Earth’s magnetic field. These waves scatter so-called “killer electrons” out of the Van Allen radiation belts, making space safer for satellites. Slower Pc3 waves are a gentle flutter caused by solar wind blowing down the flanks of the magnetosphere. (Imagine blowing across a piece of paper, making it flutter with your breath. Same idea.)

“Magnetic storms are great,” says Stammes, “but sometimes the ‘quiet’ can be just as interesting.”

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