Astro Bob: Earth sidesteps a powerful solar flare — for now
A large flare on the far side of the sun reminds us of the inevitable.
DULUTH — Late Tuesday afternoon Feb. 15, one of the cameras on the orbiting Solar and Heliospheric Observatory (SOHO) snapped photos of a massive solar eruption in the wake of a powerful flare. The explosion occurred on the sun's far side and was directed away from the Earth. Had it occurred on the near side, I'd be advising you look for the northern lights tonight.
Flares are classified by how much X-ray energy they produce. Since there are no spacecraft observing the sun's far side in X-rays, we have no idea exactly how powerful the flare was. However, we think we know where it happened.
It appears the source was a large sunspot group, possibly AR2936, the same region that gifted us a sweet aurora earlier this month. You'll recall that the material ejected from this group was also responsible for the demise of some 40 Starlink satellites — one of the more spectacular (and expensive) examples of poor launch timing.
Although we can't see the sunspot group, we know it's there because we can hear it through helioseismology . The sun is really noisy. Gobs of hot gas called plasma rise up from its interior and crash into the surface, creating ripples of low-frequency sound. The most common rumblings are spread across two-octaves and repeat every 5 minutes. While the sounds are well below the range of human hearing, we can speed them up into the audible range (example below) and literally hear the sun sing. Or grumble. Give a listen.
By tracking how the waves bounce around the sun astronomers can probe its otherwise invisible interior as well as the surface of the out-of-sight hemisphere. That brings us back to AR2936. If it was the reason for the recent CME, it will rotate back into view about Monday, Feb. 21. And if it's still shooting plasma spitballs, we may see a second bout of aurora in the coming weeks.
Whether or not that particular spot group survives, it's inevitable that a massive solar storm will occur one day and profoundly, if briefly, affect many of us. All because of our need for electricity and the power lines that deliver it.
The good news is that the only significant modern incident, where a solar flare took out a major power grid, occurred on March 13, 1989 . That night, the entire province of Quebec, Canada went dark for some 12 hours shortly after the onset of a powerful geomagnetic storm. At the same time, more than 200 U.S. grids experienced momentarily drops in power. Fortunately, the U.S. had reserves, which prevented blackouts. A few satellites also tumbled out of control for several hours. More happily, auroras lights lit up skies as far south as Florida and Cuba.
Fluctuations in the Earth's magnetic field brought on by solar storms can induce electric currents at the Earth's surface. Power lines make a perfect target, especially long lines that bring electricity to rural areas. Increased voltage flowing through the wires can damage circuits and transformers, and in the worst cases, completely shut down a grid as it did in Quebec Province.
Based on a study led by Greg Lucas, an engineer and scientist at the Laboratory for Atmospheric and Space Physics (LASP), how a power grid responds to big solar storm depends on three primary factors: the intensity and location of the storm, how well the rock beneath the transmission lines conducts electricity and the length and direction of the lines.
The 1989 storm took direct aim at northeastern Canada, stressing the Quebec grid the most while leaving U.S. transmission lines relatively unscathed. Second, sedimentary rock, the kind deposited layer-by-layer through erosion, is a fairly good conductor of electricity and helps to dissipate storm currents. Igneous and metamorphic rock, on the other hand, resist the flow of electricity. They're no help at all.
Finally, voltage adds up over long transmission lines, especially if they happen to be aligned with the direction of the magnetic field above. During a big storm you might get a modest bump of 25 volts per kilometer, but over hundreds of kilometers, that can add up to thousands of volts.
Based on this information, Lucas and colleagues identified a number of regions in the U.S. that are particularly vulnerable to geomagnetic storms. These include the East Coast, along with Wisconsin, Minnesota, and the Dakotas. All are underlain by electrically resistant rock. Lesser populated regions of the Upper Midwest states have lots of long transmission lines (to connect widely-space rural communities), making them potentially susceptible to overloading.
There are ways of dealing with the sun's temper. Stockpiling transformers so they're on hand to quickly replace damaged ones makes sense. Eight utilities created just such an emergency use reserve in 2015. Then in 2019, a presidential executive order instructed utilities to better prepare for magnetic pulses (natural and human-caused) to minimize risk and disruption.
I happen to live in northern Minnesota, home to miles-deep, non-conductive igneous rock. Perhaps it wouldn't be a bad idea to purchase a generator before the solar cycle peaks again!
"Astro" Bob King is a freelance writer for the Duluth News Tribune.