February 23, 2018
from SpaceWeather Website

Source

Yesterday, a solar wind stream grazed Earth's magnetic field.

Keyword:

graze.

The off-center impact of the solar wind caused something unusual to happen:

Earth's polar magnetic field rang like a bell...

Rob Stammes recorded the phenomenon (above image) from his magnetic observatory in Lofoten, Norway:

"On Feb. 22nd, the magnetic field around our observatory (as measured by ground currents) was swinging back an forth with a 100 second period," says Stammes.

 

"This very stable oscillation went on for more than an hour."

This is quite different from what normally happens when a solar wind stream hits Earth, head-on.

Here is an example of Stammes' recordings during a typical geomagnetic storm. Compared to the cacophany of a normal storm, yesterday's event was a sweet pure tone.

Researchers call these pure ultra-low frequency oscillations "pulsations continuous" (Pc).

Pc waves energize particles in Earth's inner magnetosphere because they resonate with the natural motion of particles around the geomagnetic field. This energy, in turn, can supercharge the aurora borealis.

Indeed, hours after the Pc waves were observed, auroras exploded over Arctic Scandinavia.

In Abisko, Sweden, Oliver Wright recorded three minutes of the display:

"I was guiding for Lights Over Lapland and we were treated to a fantastic geomagnetic storm," says Wright.

 

"The auroras were so bright I just pointed my camera at the sky and recorded the lights in real time, hand-held."

The effect of the solar wind stream may be likened to a person blowing across the top of a soda bottle, the grazing breath producing a nearly monochromatic waveform.

"This is quite rare," says Stammes.

 

"Pulsating continuous signals like these are visible only 2 or 3 times a year."