Solar flare on Friday. (NASA Solar Dynamics Observatory via SpaceWeather.com)

Early Friday, a sunspot region unleashed a sizable solar flare as well as a wave of charged particles, known as a coronal mass ejection. It could spur aurora in parts of the northern United States late this weekend.

The originating solar flare’s intensity was minor, rated 1 out of 5 on the R-scale, which indicates the amount of disruption such flares have on high-frequency radio communications. Though not particularly energetic, this flare is noteworthy as the sun has been exceedingly quiet this year. It is near the least-active part of its roughly 11-year cycle.

The sunspot region, known as NOAA Region 2665, which triggered this activity had been largely quiet throughout its transit across the solar disk. Apparently an instability arose that triggered Friday’s eruption.

What’s important here is the location of the solar eruption as we look back from earth. The site was near the best-connected interplanetary magnetic field line, so protons from the eruption made their way to earth. They have spurred a minor solar radiation storm, rated 1 out of 5 on the S-scale, an indicator of the storm’s energy in space. This is not a big response, but enough to impede high-frequency radio communications, used by some airlines as they fly polar routes Friday.

The coronal mass ejection, still en route, originated near enough to the center of the sun’s disk so that it is on a path to fly by earth. It is expected to arrive July 16 and 17. The National Oceanic and Atmospheric Administration’s Space Weather Prediction Center has issued a geomagnetic storm watch and predicts a moderate storm, rated 2 out of 5 on the G-scale, which indicates the intensity of the magnetic disturbance.


Animation of coronal mass ejection, July 14, 2017. (NASA via SpaceWeather.com)

When the geomagnetic storm arrives, it may incite aurora in the mid- to high latitudes — most likely Sunday night.


(Space Weather Prediction Center)

So have a look for auroras if you’re in the northern United States and in a dark spot (the moon is in its last quarter, so that helps).

Had these solar pyrotechnics occurred last week, the effects would have missed Earth and been negligible; as the real estate agents say, it’s “location, location, location.”

This flurry of activity occurs on Bastille Day, July 14. It harks back to an earlier Bastille Day eruption in 2000, nearer the maximum of the last solar cycle, when the sun erupted with an incredible R-3, S-3, G-5 trifecta — many times more powerful than this year’s event.

But now, as we’re near the solar minimum, such events are rare. Bastille Day fireworks, you bet!