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An M-class (medium to large) coronal mass ejection erupting from the sun on 31 August 2012.

An M-class (medium to large) coronal mass ejection erupting from the sun on 31 August 2012.


A geomagnetic storm is coming—should I worry?

The National Oceanic and Atmospheric Administration’s (NOAA’s) Space Weather Prediction Center (SWPC) is forecasting a moderate to strong geomagnetic storm to occur sometime later today or tonight, U.S. Eastern time. What does that mean? Will it knock out power grids? Will there be a lot of radiation? Your questions, answered.

Q: What causes a geomagnetic storm?

A: The sun is now just about at the peak of its 11-year solar cycle, meaning that there are a significant number of sunspots visible. Sunspots look like dark freckles on the sun, but they’re actually regions of intense magnetic activity. Clusters of these sunspots can be sources of solar flares and coronal mass ejections (CMEs), sudden bursts of energized particles that swiftly stream out from the surface of the sun. The largest type of these is called an X-class flare. If an X-class flare is powerful enough and aimed directly at Earth, it can cause radiation storms in Earth’s ionosphere and wreak havoc with radio communications.

Q: So what’s happening today?

A: According to Thomas Berger, the director of SWPC in Boulder, Colorado, there were two back-to-back CMEs from the sun earlier this week, the second of which produced an X-class flare yesterday at about 1:45 p.m. It’s expected to reach Earth later this morning or early afternoon.

Berger noted yesterday at a NOAA press conference that this X-class flare is not expected to produce a particularly large event, as these things go; there are perhaps 100 to 200 of this size of geomagnetic storm in a given solar cycle. (This one’s rated a G3, on a scale of 1 to 5.) “It’s expected to be manageable and not cause any major interruptions to power transmission,” he said. But he added that space weather scientists are paying closer attention to this event than might otherwise be warranted because two back-to-back CME events, both directed at Earth, is a bit more unusual, and because it’s possible that the two could interact on their way to Earth. The second, more powerful event is also traveling faster than the first and could overtake it (although current models suggest it won’t).

Q: Should people flying in planes today worry about radiation?

A: No. There are different types of space weather—geomagnetic storms, which affect communications, and solar radiation storms. Although this is expected to be a G3-level geomagnetic storm, it’ll only be an S1 solar radiation storm. Airlines (and astronauts) have procedures in place for storms level S3 and above. 

Q: What about aurorae? Will we see pretty lights?

A: Maybe! You need clear skies, but it’s possible that if you’re far north enough you’ll see aurorae tonight. For example, in the United States, Berger said, for a storm this size, it could be visible at night along the northern tier states bordering Canada, but it’s unlikely to be visible farther south.