atmosphere
A musical note from our atmosphere. Around 05.30 UTC or 06.30 local time magnetic and ground current pulsations on my instruments. Approximately 2 hours long and with a period time of 2 minutes and 14 seconds. Continuous geomagnetic ULF pulsations in the range between Pc4 and Pc5. For the first time this year and sometimes only once a year.It's great to see that our atmosphere can make this happen. This phenomenon can also be seen on other magnetometers for example from Abisco and Kiruna,roughly in the same place of the auroral oval.
High above the Arctic Circle in Lofoten, Norway, citizen scientist Rob Stammes operates a space weather monitoring station. His sensors detect ground currents, auroras, radio bursts, and disturbances in Earth's magnetic field. Yesterday, he says, "I received a musical note from the magnetosphere."

"Around 05.30 UTC on Jan. 18th, our local magnetic field began to swing back and forth in a rhythmic pattern," he says. "Electrical currents in the ground did the same thing. It was a nearly pure sine wave--like a low frequency musical note. The episode lasted for more than 2 hours."

Stammes has received such notes before, but they are rare. "I see a pattern like this only about once a year," he says.

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 does the same thing to magnetic fields. Pc waves are essentially flutters propagating down the flanks of Earth's magnetosphere excited by the breath of the sun.

magnetometer
A magnetometer in Abisko, Sweden, recorded the same waves.
Yesterday's set of waves washed over Norway and Sweden, but almost nowhere else, according to the global INTERMAGNET network of magnetometers. It was a strictly regional phenomenon.

What happens in the sky when such a pure tone emerges from the natural background cacophony of magnetic activity? "I wish I knew," says Stammes. "I was asleep at the time." In fact, it's possible that no one knows. Tones like these are rare, and they all too often occur while skies are cloudy or daylit, blocking any peculiar auroras from view. Stammes says he plans to build an alert system to help him find out. No pun intended: Stay tuned.