When a stream of solar wind hits Earth's magnetic field, magnetometers around the Arctic Circle normally go a bit haywire, with their needles swinging chaotically as the buffeting ensues. Rob Stammes of the Polarlightcenter, a magnetic observatory in Norway, sees such disordered behavior all the time. But on Nov. 18th something quite different happened. The solar wind produced a pure sine wave:
"A very stable ~15 second magnetic oscillation appeared in my recordings, and lasted for several hours," he says. "The magnetic field was swinging back and forth by 0.06 degrees, peak to peak."
Imagine blowing across a piece of paper, making it flutter with your breath. The solar wind can have a similar effect Earth's magnetic field. The waves Stammes recorded are essentially flutters propagating down the flanks of our planet's magnetosphere excited by the breath of the sun. Researchers call them "pulsations continuous" -- or "Pc" for short..
"A sensitive magnetometer is required to record these waves," says Stammes. "I use a mechanical magnetometer with bar magnets suspended from a special wire. LEDs and light detectors in an isolated dark box record the motion of the magnets, while vanes in oil damp out non-magnetic interference."
Pc waves are classified into 5 types depending on their period. The Nov. 18th waves fall into category Pc3. Researchers have found that Pc3 waves sometimes flow around Earth's magnetic field and cause a "tearing instability" in our planet's magnetic tail. This, in turn, sets the stage for an explosion as magnetic fields in the tail reconnect.
Imagine blowing across a piece of paper, making it flutter with your breath. The solar wind can have a similar effect Earth's magnetic field. The waves Stammes recorded are essentially flutters propagating down the flanks of our planet's magnetosphere excited by the breath of the sun. Researchers call them "pulsations continuous" -- or "Pc" for short..
"A sensitive magnetometer is required to record these waves," says Stammes. "I use a mechanical magnetometer with bar magnets suspended from a special wire. LEDs and light detectors in an isolated dark box record the motion of the magnets, while vanes in oil damp out non-magnetic interference."
Pc waves are classified into 5 types depending on their period. The Nov. 18th waves fall into category Pc3. Researchers have found that Pc3 waves sometimes flow around Earth's magnetic field and cause a "tearing instability" in our planet's magnetic tail. This, in turn, sets the stage for an explosion as magnetic fields in the tail reconnect.
A quartet of NASA spacecraft recently flew through just such an explosion. Last week, researchers from the University of New Hampshire reported that four Magnetospheric Multiscale (MMS) spacecraft spent several seconds inside a magnetic reconnection event as they were orbiting through Earth's magnetic tail. Sensors on the spacecraft recorded jets of high energy particles emerging from the blast site. One jet was aimed squarely at Earth and probably sparked auroras when it hit the upper atmosphere.
Stammes has recorded many Pc waves in the past, "but this is the first time I have detected category Pc3," he says. "This was a very rare episode indeed."
www.spaceweather.com
Stammes has recorded many Pc waves in the past, "but this is the first time I have detected category Pc3," he says. "This was a very rare episode indeed."
www.spaceweather.com
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