For skywatchers in the United States as far south as Northern Virginia and Illinois, last Saturday night was slated to be memorable.
Except… it wasn’t.
For days, local and national media outlets had been heralding an anticipated display of the ethereal aurora borealis – more commonly known as the northern lights.
A blast of plasma launched from sunspot region AR2736 – a bruise on the sun throbbing with pulses of magnetic energy – appeared to be targeting earth. The high-energy particles were seen by the National Oceanic and Atmospheric Administration’s Space Weather Prediction Center, which hoisted a watch the prior Wednesday outlining potential for a moderate geomagnetic storm on earth.
The blast, known as a coronal mass ejection, hurled a burst of protons and electrons into space in the direction of earth. When these charged particles bombard the earth’s upper atmosphere, the planet’s magnetic field can convert potentially harmful energy to visible light. That’s the aurora. The more intense the solar blast, the farther south the northern lights dip. On rare occasions, the Lower 48 is treated to its mystical emerald dance.
USA Today advertised the “rare chance to see the northern lights,” while Insider asserted they could shimmer as low as Chicago and New York. NBC News announced the aurora borealis had odds of reaching “far south."
But the sky never delivered. Who knows how many people shivered beneath a bright moon staring upward until the frigid weather trumped their patience. The solar blast didn’t hit Earth until Sunday evening and, even then, did not spark a geomagnetic storm that triggered northern lights.
Why the busted forecast? It was a combination of scientific uncertainty and ill-based media hype.
“Space weather forecasting is where terrestrial weather forecasting was back in the 1960s,” wrote Tamitha Skov, an expert in space weather, in an email. She explained the challenges in observing solar storms, and why it makes predicting their impacts so difficult.
“We essentially have something akin to a ‘tornado siren’ when forecasting these events,” she wrote. “We see them launch off of the Sun and can estimate their initial speed for a very small window of time as they are launched. Why such a small time window? Sadly, it’s the only time we really see them well enough to make measurements.”
The next data we get isn’t until a solar storm reaches earth-orbiting satellites like DSCOVR. These platforms can offer live monitoring of a number of parameters. But their proximity to earth limits usefulness, offering no more than an hour’s warning before the solar storm hits. It’s like having a buoy at the end of a dock to measure an incoming tsunami.
“After [they launch], solar storms aren’t truly visible to us forecasters again until days later, when they pass by our upstream satellite monitors very close to Earth,” explained Skov. “This means the intervening 92 million miles between the Sun and the Earth are an observational ‘dead zone’ when it comes to real-time forecasting. We simply cannot see how far the solar storm has traveled, or what it’s encountered along the way.”
Skov illustrates how difficult it is to fill in the gap. “Imagine trying to predict [the ETA of] someone traveling cross-country from L.A. to Washington DC,” she said. “They’re dealing with freeways, back roads, rush-hour traffic, collisions, bad weather… you name it. All you have to estimate their arrival time is the speed at which they backed their car out of the driveway.”
It comes as no surprise that accurate predictions of space weather and auroral activity are hard to come by. But Skov, creator of the popular site SpaceWeatherWoman.com, is trying to change that. She’s built a following of 50,000 followers, whom she taps for current observations from all around the globe. She stressed the importance of citizen scientists in the endeavor, whose help she has enlisted to make better short-term aurora forecasts during big events.
But forecasting hurdles weren’t the only thing that led to Saturday’s letdown. Media hype also brewed hope in regions that wouldn’t have seen the lights even had the forecast come to full fruition.
The Space Weather Prediction Center called for a G2 storm. What’s that mean? An index used to measure geomagnetic activity should peak at a 6 on a 0-9+ scale. For reference, this happens an average of 360 days every 11 years. Do we see the northern lights every week and a half in the contiguous United States? Nope.
But the media ran with it, likely due in part to how quiet the sun has been lately. It’s just like how the first snow of a season is noteworthy. Snow isn’t special, but any disruption to a quiet spell becomes news.
“I think the reason the media so often overstates the likelihood of aurora is that, when they do get it right, their readers are just wildly impressed,” wrote Joe Kunches, space weather expert for Capital Weather Gang. “The phenomenon is so striking, so brilliant — kind of like seeing Elvis. Unforgettable.”
Theoretically, a G2 storm – one of the level that was forecast last weekend – would spill the lights to around the U.S./Canada border. But the operative word is visible, and seldom is seeing them as easy as it may seem.
“You need a dark sky with little background lighting, a dull moon, few clouds, and have to be watching a the right time,” Kunches emphasized.
And more often than not, the flashy images you see from U.S. locations get a little help from the camera. Longtime exposures can capture faint auroral glows that would be imperceptible to the naked eye.
Once and a while, though, those of us at the mid-latitudes can get lucky.
“I don’t want people to think they will never see aurora if they live in the U.S.,” wrote Skov. “That would be just as false as the hype we had over this latest storm.”
On June 22, 2015, a geomagnetic storm climbed to a G4, with geomagnetic KP indexes ranging between 8 and 9 out of 9. Visible northern lights dipped as far south as southern New England, making for an hour of white and green shimmering curtains.
One solar storm in 1859, known as the Carrington event, brought the northern lights as far south as Hawaii and Florida! In Washington, D.C., it was reportedly possible to read a newspaper at midnight, illuminated by the green waves above. If a storm of similar magnitude happened again today, the results could be disastrous, crippling earth’s power grid.