On Monday night, skywatchers were treated to a moderate display of the northern lights. For those who missed out, there’s still a chance they may be visible again tonight, with a stronger geomagnetic storm forecast.
The U.S. National Oceanic and Atmospheric Administration’s (NOAA) Space Weather Prediction Center (SWPC) is forecasting a strong geomagnetic storm. (Monday’s was considered moderate.)
The sun has been quite active, with many sunspots on its surface. Sometimes, those spots unleash a solar flare. These large eruptions of electromagnetic radiation can last minutes to hours, and can disrupt some radio transmissions on Earth.
Quite often, these flares are followed by a coronal mass ejection (CME), a large expulsion of particles from the sun that travel faster than normal on the solar wind. When those particles reach Earth, they interact with our magnetic field and can create beautiful northern lights, or aurora borealis.
In this case, two CMEs were unleashed on the sun on Aug. 30 and headed toward Earth.
According to Tamitha Skov, a space weather physicist and professor at Millersville University in Pennsylvania, neither of the eruptions looked to be of any real significance at first. However, further study shows that the second eruption was more powerful than initially appeared.
“The second and much larger storm has a hidden surprise,” Skov said in a YouTube video. “Its signature during the eruption and later in coronagraph imagery signals that there may be quite a bit of coronal material on its way to us.”
Monday’s geomagnetic storm was a G2 on a storm scale of one to five. The SWPC is forecasting a G3 geomagnetic storm for Tuesday night.
Difficulty forecasting auroras
Now, auroras are notoriously difficult to forecast, so there’s no guarantee that we will get a show tonight. However, several apps can tell you if they are visible in your area, including Aurora Alerts and Aurora Now.
Many people will likely remember the amazing displays of the northern lights on May 10, 2024 and Oct. 10, 2024. Both of those storms reached G5. Initial forecasts for the pair had them reaching G3 or G4, an example of just how difficult it can be to forecast accurately.
On both of those occasions, the northern lights were visible across Canadian and U.S. cities and went as far south as Mexico.
As for this storm forecast, the first one impacted Earth on Monday, but the second is anticipated for Tuesday.
“We are anticipating a one-two punch from those two solar storms that are headed toward Earth,” Skov said. “At high latitudes, NOAA is expecting severe storm conditions. This is starting right around [Sept. 2].”
That bodes well for Canadians, with a few cities at high latitudes. And for the many cities in what are considered mid latitudes, NOAA is also predicting a 50 per cent chance of a strong geomagnetic storm over the next 24 hours. For those in high latitudes, it rises to 85 per cent.
Several factors
A lot of things have to happen for those in mid-latitudes to see the aurora, including how fast that solar wind is moving and whether the auroral oval — along which these particles interact with molecules that produce the colours of the lights — tips south. The further south the hole dips, the further south the aurora are seen.
In order to determine how strong a geomagnetic storm is, NOAA uses the Kp index, which ranges from one to nine. The stronger the storm, the higher the number. For those in mid-latitudes, typically the number needs to be Kp 6 or higher, unless conditions are ideal. You can check the SWPC’s site to see what that number is.
As of writing, the Kp was at four, with the auroral oval dipping into northern Europe.
So, fingers crossed the storm persists for Canadians.
“Aurora photographers could get a great show if the magnetic field of this storm is favourably oriented, even down into mid-latitudes,” Skov said.
