An image of the sun on Tuesday. (NASA, labels by CWG)

A large, previously active sunspot has rotated toward Earth over the past week, elevating our solar flare and geomagnetic storm chances in an otherwise quiet period of space weather.

Sunspot AR2339 is the largest sunspot on the Earth-visible side, and has been been grumbling out some low-level, C-class flare activity with minor radio impacts over the past couple of days. It hasn’t produced any large flares since one week ago when it whipped out an X-class flare just after coming into view on the Sun’s horizon. The X2 flare did have an associated coronal mass ejection, but since it was pointed out into space, Earth did not get a geomagnetic storm (or aurora) from the event.

[Sunspot AR2339 ejects intense X-class flare]

Given AR2339’s size — much larger than the planet Earth itself — and its recently active history, the Space Weather Prediction Center is forecasting a 30 percent chance of at least an M-class solar flare over the next two days, and a five percent chance of an X-class flare.


A telescope view of sunspot AR2339, with an image of the Earth to-scale. (Tosi philippe via spaceweather.com )

High-latitude skywatchers will likely continue to see some active aurora nights over the next couple of days. “An interplanetary shock wave hit Earth’s magnetic field during the early hours of May 12th,” says spaceweather.com, “setting the stage for auroras. NOAA forecasters estimate a 60% chance of geomagnetic storms.”

The increase in geomagnetic storming — and associated auroras for the high-latitudes — is mostly due to the solar wind activity from coronal holes.


An intense green and purple aurora seen over Edmonton in Alberta, Canada on Tuesday morning. (Zoltan Kenwell via spaceweather.com )

“Coronal holes are basically large ‘nozzles’ on the Sun for high-speed solar wind,” says Joe Kunches, our space weather expert. “They don’t erupt suddenly like solar flares, but rather emit a constant and fast solar wind. Solar wind typically flows at about one million miles per hour, but through coronal holes it can be twice as fast.”

[Coronal hole season is just heating up]

The Space Weather Prediction Center says the solar wind environment is forecast to become more active “due to the onset of a co-rotating interaction region.” Spaceweather.com describes these regions as “transition zones between fast- and slow-moving solar wind streams. Solar wind plasma piles up in these regions, producing density gradients and shock waves that do a good job of sparking auroras.”