There was no solar storm or geomagnetic storm to cause the disturbance. So what was it?
Lately, Earth's magnetic field has been quiet. Very quiet. The sun is in the pits of what may turn out to be the deepest Solar Minimum in a century. Geomagnetic storms just aren't happening.
"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."
This chart recording shows a magnetic wave rippling through Preston UK on June 23, 2020. Credit: Stuart Green.
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," he says.
"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."