In recent times the Earth’s magnetic field has been quiet. Actually, 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 are not happening.
That’s why Stuart Green, who operates a research-grade magnetometer at his house in Preston, UK, was so surprised on 23 June when his instruments picked up a magnetic anomaly. “For more than 30 minutes, the local magnetic field oscillated like a sine wave.”
Dr Pieter Kotze, researcher at SANSA Space Science, confirmed that all four observatories at Hermanus, Hartebeesthoek, Keetmanshoop and Tsumed observed these pulsations on 23 June 2020. He said it was particularly evident in the X-component. Indications are that this was a global phenomenon.
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.”
Magnetic observatories around the world detected the wave on June 23, 2020.
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 a silent room.
Solar wind, incoming: Minor geomagnetic unrest is possible on 30 June and 1 July when a stream of solar wind gently buffets Earth’s magnetic field. The gaseous material is flowing from a small hole in the sun’s atmosphere. Antarctic sky watchers should be alert for auroras in austral winter darkness.