The Earth’s magnetic field has been quiet lately. Very quiet. The sun is in a deep minimum of activity, which may be the deepest solar minimum in a century.
Geomagnetic storms simply do not exist. But on June 23, something unusual was recorded. The Earth’s magnetic field swung back and forth by about 1/3 of a degree.
“That’s why I was so surprised on June 23 when my instruments detected a magnetic anomaly,” said Stuart Green, who works with a research-class magnetometer in his home in Preston, UK.
“For more than 30 minutes, the local magnetic field oscillated like a sine wave.”
Green quickly checked the solar wind data from the NOAA DSCOVR satellite.
“There was nothing – no surge in solar wind speed or other factors that could explain this disturbance,” he says.
He was not the only one to notice this. In the Lofoten Islands of Norway, Rob Stams found a similar anomaly on his magnetometer.
“It was amazing,” says Stams. “Our magnetic field swung back and forth by about 1/3 of a degree.” I also discovered ground currents with the same 10 minute period.”
Space physicists call this phenomenon “pulsation.” Imagine that you are blowing on a piece of paper, making it flutter from your breath. Solar wind can have a similar effect on magnetic fields. During the extreme silence of the solar minimum, such waves can be “heard” like a pin falling in a quiet room.
The Earth’s magnetic field was so quiet on June 23 that this ripple was heard all over the world. The INTERMAGNET global network of magnetic observatories recorded wave activity simultaneously from Hawaii to China and the Arctic Circle and even in Antarctica.
PC waves are classified into 5 types depending on their period. The 10-minute wave June 23 falls into the Pc5 category. Slow Pc5 waves were associated with the loss of particles from Van Allen’s radiation belts. Energy electrons beat these waves down into the Earth’s atmosphere, where they scatter.