The off-center impact of the solar wind caused something unusual to happen:
Rob Stammes recorded the phenomenon (above image) from his magnetic observatory in Lofoten, Norway:
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:
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.