Evolution of a Coronal Hole

Dec. 26, 2016: Christmas 2016 was special for sky watchers around the Arctic Circle.  The skies filled with some of the best Northern Lights of the year, including rare outbursts of white and pink. The source of the display: A giant “coronal hole” in the sun’s atmosphere sprayed our planet with solar wind. The hole opened up in July 2016 and it has been strobing Earth with solar wind every ~28 days ever since as the hole pirouettes with the slowly rotating sun.

Spaceweather.com reader Stuart Green has prepared a plot showing the evolution of the coronal hole and the effect it has had on the magnetic field at his private observatory in Preston, England.  Click on the image to inspect the full 6 months:

Inset images come from NASA’s Solar Dynamics Observatory. The coronal hole is the giant dark region, starting small in July, then growing and shape-shifting as the year unfolds.

The background strip chart recording shows the instability of the magnetic field around Green’s private observatory. When the coronal hole is facing Earth, big changes are measured.

“I’ve been recording geomagnetic activity over the past three years using a home built/ home designed magnetometer,” says Green. “The sensor is buried in my garden about 0.5m below the surface in an East/West orientation to allow very sensitive (sub nanotesla) measurements of magnetic declination during geomagnetic storms. The plots show the change in magnetic flux density in nanotesla occurring between readings every 2.5 minutes.”

Green’s presentation suggests that this yawning hole is a long-lived feature on the sun, and it will probably be back as potent as ever 28 days from now.  Stay tuned for magnetic unrest–and more Arctic auroras–in January.