The sun unleashed a powerful eruption early on Oct. 6, launching a coronal mass ejection (CME) toward Earth — and it could give the northern lights a boost later this week.
NOAA's Space Weather Prediction Center (SWPC) has issued a moderate (G2) geomagnetic storm watch for Oct. 9, when the CME is expected to reach Earth.
The eruption accompanied an M1.4-class solar flare from sunspot region AR4549, which is currently positioned close to the center of the Earth-facing side of the sun.
Forecasters at Belgium's Solar Influences Data Analysis Center (SIDC) estimate the CME is travelling at around 560 km/s.
Current models put the CME's arrival in the early hours of Oct. 9 (UTC), although there is still uncertainty over the exact timing.
The U.K. Met Office currently predicts an arrival at around midnight EDT (0400 GMT), give or take 6 hours.
So don't set your alarm quite yet — CME arrival forecasts can shift by several hours as the eruption approaches.
Space weather forecasters are busy analyzing coronagraph observations and models to determine the CME's trajectory and speed, and updating the possible arrival time at Earth. That's when we'll have a much better idea of what this eruption could mean for the northern lights.
If a substantial part of the CME is Earth-directed, it could trigger a geomagnetic storm and send auroras into lower latitudes than usual. Just how impressive the display could be will also depend heavily on the magnetic orientation of the CME when it reaches Earth.
What could this mean for the northern lights?
NOAA's SWPC currently expects minor (G1) to moderate (G2) geomagnetic storm conditions on Oct. 9, with a G2 watch now in effect.
Geomagnetic storms are ranked on a scale 1-5, from G1 (minor) to G5 (extreme). G2 conditions correspond to Kp 6, and auroras have previously been seen as far south as New York and Idaho during storms of this strength.
This doesn't mean the northern lights are guaranteed to reach these states, nor does it mean they won't stretch even farther south. The extent of the show will depend on how the incoming CME interacts with Earth's magnetic field.
Even an Earth-directed CME doesn't guarantee an impressive geomagnetic storm and subsequent aurora shows. Much will depend on the strength and orientation of the magnetic field carried by the CME when it reaches Earth, particularly if it has a southward component that can couple efficiently with Earth's magnetosphere.
For now, aurora chasers should keep a close eye on the forecasts for Oct. 9.
When could the northern lights be visible?
NOAA's latest 3-day forecast shows:
- G1 conditions between 11 p.m. and 2 a.m. EDT on Oct. 8-9) (0300-0600 GMT)
- possible G2 peak between 5 a.m. and 8 a.m. EDT (0900 and 1200 GMT) on Oct. 9.
These timings are estimates and could change as the CME approaches.
Aurora forecast for the Northern Hemisphere courtesy of the U.K. Met Office
More solar activity could be on the way
And this might not be all the sun has in store for us.
At the time of writing AR4549 produced another M-class solar flare, an M1.8, just hours after the eruption we're currently keeping a close eye on.
Two prominent sunspot regions, AR4549 and AR4545, are currently facing Earth and have shown increasing flare activity. Any additional eruptions from these regions over the next few days could affect Earth. Meanwhile, coronal holes rotating across the Earth-facing side of the sun are expected to send further streams of fast solar wind our way, with another enhanced period of geomagnetic activity predicted around Oct. 11.
In other words, make sure those camera batteries are charged, your aurora alerts switched on and the coffee pot is full!
Editor's note: This story was updated at 4 a.m. EDT (0800 GMT) on Oct. 7 to include NOAA's Space Weather Prediction Center's G2 (moderate) geomagnetic storm watch for Oct. 9. We will continue to update this story as new forecasts become available.