"That's why I was so surprised on June 23rd when my instruments picked up a magnetic anomaly," reports Stuart Green, who operates a research-grade magnetometer in his backyard in Preston UK. "For more than 30 minutes, the local magnetic field oscillated like a sine wave."
Green quickly checked solar wind data from NOAA's DSCOVR satellite. "There was nothing-no uptick in the solar wind speed or other factors that might explain the disturbance," he says.
He wasn't the only one who noticed. In the Lofoten islands of Norway, Rob Stammes detected a similar anomaly on his magnetometer. "It was remarkable," says Stammes. "Our magnetic field swung back and forth by about 1/3rd of a degree. I also detected ground currents with the same 10 minute period."
What happened? Space physicists call this phenomenon a "pulsation continuous" or "Pc" for short. Imagine blowing across a piece of paper, making it flutter with your breath. Solar wind can have a similar effect on magnetic fields. Pc waves are essentially flutters propagating down the flanks of Earth's magnetosphere excited by the breath of the sun. During more active phases of the solar cycle, these flutters are easily lost in the noise of rambunctious geomagnetic activity. But during the extreme quiet of Solar Minimum, such waves can make themselves "heard" like a pin dropping in an silent room.
Comment: Earth's magnetic field is weakening for unexplained reason says ESA