Solar storm brings aurora borealis to Siouxland

Curtains of vaguely green-ish and sometimes pink-ish auroras could be seen dancing in the skies in rural areas outside Sioux City late Sunday night. Photos captured their beauty, color and intensity better than the naked eye could perceive; still, the lights were quite visible to the unaided eye from the right viewing place. 

Auroras are the result of solar wind interacting with the Earth's magnetosphere and its outer atmosphere. The visual phenomenon is more common at the far northern or far southern latitudes. 

Sunday's geomagnetic solar storm reached a G4 intensity on the National Oceanic and Atmospheric Administration's Geomagnetic Scale -- considered "severe," and only one ranking below the most-powerful storms, which are rated G5. Even G5 storms aren't particularly uncommon, occurring about four times during each 11-year solar cycle, according to the National Weather Service. 

Auroras were reported across parts of Europe and Asia during Sunday's sun storm. In the U.S., skygazers took in the sights from Wisconsin, Washington state, Colorado, California, New Mexico and even Arizona.

Solar activity had settled down by Monday, though auroras remained a possibility in South Dakota and Iowa into late Monday and early Tuesday. 

The sun operates on roughly 11-year cycles, vacillating between periods of high sunspot activity and comparative calm. The most-intense period in the cycle is called the solar maximum; the least-active period is the solar minimum. The most recent solar minimum was in late 2019; solar maximum is expected to occur either in 2024 or 2025. At present the sun is in an increasingly active phase, as it were. 

"Then we reach what we call a solar maximum, where it's producing a lot of sun spots, and those sun spots produce coronal mass ejections, or CMEs. That's this pulse of electromagnetic radiation that comes, hits, the Earth's atmosphere, and we get the aurora," said Matthew Meyers, a meteorologist with the National Weather Service in Sioux Falls. "And again, more sunspots means more coronal mass ejections. Doesn't always they hit Earth." 

Bill Murtagh, program coordinator at the NOAA Space Weather Prediction Center in Boulder, Colorado, told the Associated Press that, with the solar cycle ramping up, there could be more opportunities in the coming years to see auroras. 

“Stay tuned, more to come,” he said.

Intense solar storms can also be quite problematic. In early September, 1859, the most powerful solar flare known in history, referred to as the Carrington Event, caused telegraph lines to malfunction and made compass needles swing erratically, according to the NOAA.

Some telegraph equipment threw off sparks, setting nearby papers on fire, or gave shocks to their operators. The lines and equipment were over-energized by the solar flare. At one point, two telegraph operators, one in Boston and the other in Portland, Maine, were able to send messages to each other with the power supply to their equipment turned off. In other places, messages couldn't be transmitted at all. 

The Carrington Event also produced intense auroras, and contributed significantly to early scientific knowledge of solar flares. 

Such a thing could still happen, in a world far more crisscrossed by wires and dependent on electricity and telecommunications than it was in 1859. Partly because of that risk, the NOAA Space Weather Prediction Center monitors solar activity closely. 

An unusually severe solar flare could bring about problems with everything from pipelines to radio communications to satellite navigation. 

"From an infrastructure standpoint, there's possible widespread voltage-control problems that could mistakenly trip out key assets from the grid," Meyers said.

The Associated Press contributed reporting.