April 30, 2021: Imagine living in Florida. You’ll never see the Northern Lights … right? Actually, the odds may be better than you think. A new historical study just published in the Journal of Space Climate and Space Weather shows that great aurora storms occur every 40 to 60 years.

“They’re happening more often than we thought,” says Delores Knipp of the University of Colorado, the paper’s lead author. “Surveying the past 500 years, we found many extreme storms producing auroras in places like Florida, Cuba and Samoa.”

This kind of historical research is not easy. Hundreds of years ago, most people had never even heard of the aurora borealis. When the lights appeared, they were described as “fog,” “vapors”, “spirits”–almost anything other than “auroras.” Making a timeline 500 years long requires digging through unconventional records such as personal diaries, ship’s logs, local weather reports–often in languages that are foreign to the researchers.

“We defined a ‘Great Storm’ simply as one in which auroras were visible to the unaided eye at or below 30 degrees magnetic latitude,” says Knipp. 

Visual sightings were key. The human eye is a sensor we’ve had in common with observers since the beginning of recorded history. Pre-modern scientists didn’t have satellites or magnetometers to measure solar storms, but they could look up at the night sky. In all, Knipp’s team tallied 14 examples of storms where many people saw auroras within 30 degrees of the equator.

“There may be more,” she notes. “For example, I am aware of a low latitude event that occurred between February and April 1648. It’s not on the timeline, though, because we haven’t yet been able to pin down the date.”

Look at the timeline again; there’s a whole cluster of sightings in Sept. 1770. “The Great Storm of 1770 appears to be a 500-year event,” says Knipp. “There were low-latitude auroras for 9 nights in a row.”

During the 1770 storm, extremely bright red auroras blanketed Japan and parts of China. Captain James Cook himself saw the display from the HMS Endeavour near Timor Island, south of Indonesia. Knipp’s colleague Hisashi Hayakawa (Nagoya University) has found drawings of the instigating sunspot; it is twice the size of the sunspot that caused the infamous Carrington Event of 1859. Knipp’s timeline suggests that this was not “just another Great Storm”; something exceptional happened in 1770 that researchers still don’t fully understand.

Today’s senior space weather researchers were taught in school that Great Storms are rare. The Carrington Event was long thought to be a singular event, alone in the historical record. Recent studies are finding otherwise. Just last month Jeffrey Love of the US Geological Survey published a paper in the research journal Space Weather showing that extreme geomagnetic storms recur every ~45 years or so–a result in accord with Knipp’s. He used completely different techniques (extreme value statistics and magnetometer records) to reach a similar conclusion. 

The last Great Storm in Knipp’s timeline occurred 32 years ago. Soon, it will be time for another. Stay tuned.

April 20, 2021: Sunspot AR2816 erupted during the late hours of April 19th (2342 UT), producing a strong M1-class solar flare. NASA’s Solar Dynamics Observatory recorded the extreme ultraviolet flash:

This is one of the strongest flares of young Solar Cycle 25. A pulse of X-rays and ultraviolet radiation from the flare ionized the top of Earth’s atmosphere, causing a shortwave radio blackout over the Pacific Ocean: blackout map. Mariners and ham radio operators in the area might have noticed unusual propagation at frequencies below ~20 MHz.

Interestingly, during the radio blackout the sun generated its own burst of radio noise. Shock waves from the solar flare rippled through the sun’s atmosphere, creating plasma instabilities and natural radio emissions; NOAA reports the detection of Type II and Type IV bursts. These radio bursts may have penetrated the blackout, causing roars of static in the loudspeakers of shortwave radios at the same time that normal terrestrial signals were suppressed. Research shows that solar radio bursts can interfere with the navigation of whales.

The explosion also hurled a coronal mass ejection (CME) into space. In this SOHO coronagraph movie, watch Mercury emerge from behind the occulting disk at about the same time as the CME:

UPDATE: Using these images, NOAA analysts have modeled the CME and determined that it will not hit Earth. Auroraphiles may be disappointed, but here’s some good news: With the increasing pace of solar activity, it’s only a matter of time before the sun sends a CME in our direction. Stay tuned. Aurora alerts: SMS Text.

April 16, 2021: You probably think Solar Cycle 25 is a dud. Think again. Despite long stretches of spotless quiet, the new solar cycle is actually running ahead of schedule. In this plot, the red curve shows NOAA’s predicted sunspot counts for Solar Cycle 25; the orange curve shows the new best fit:

“The sun is performing as we expected–maybe even a little better,” says Lisa Upton of Space Systems Research Corporation. She’s a co-chair of the NOAA/NASA Solar Cycle 25 Prediction Panel. “In 2019, the panel predicted that Solar Cycle 25 would peak in July 2025 (± 8 months) with a maximum sunspot count of 115 ± 10. The current behavior of the sun is consistent with an early onset near the beginning of our predicted range.”

If current trends hold, Solar Cycle 25 could peak as early as 2024, similar in strength to the relatively weak cycle (SC24) that preceded it. Don’t be fooled by the adjective, however. It’s like hurricane season. Even a “weak” season produces hurricanes–and all it takes is one good storm to do a lot of damage.

“I’m not surprised that people are grumbling about SC25 being a dud,” says Upton. “Weak cycles are typically preceded by long stretches of spotless days, and they are slow to ramp up. All of this is consistent with our prediction.”

Now the waiting begins. As sunspot counts increase over the next year, forecasters will be able to tell if Solar Cycle 25 is *really* following the official prediction or doing something completely different. Predicting the solar cycle is still an infant science, and much uncertainty remains.

Stay tuned.

April 7, 2021: Spring is the season for sprites, and Paul Smith just photographed a magnificent display over Kansas. “These were my first big sprites of the season,” says Smith, who took this picture on April 6th:

“They were so bright, I saw a couple of them with my unaided eyes,” he adds.

Sprites are a weird form of lightning that leap up from powerful thunderstorms. The ones Smith saw are “jellyfish sprites”, named for their resemblance to sea creatures. Their red tentacles stretch about 90 km high, almost touching the edge of space. Other forms exist, too.

At this time of year, severe storms set the stage for sprite formation. Mesoscale convective systems sweep across the Great Plains, cracking with intense electric fields that drive electrons up and into sprites. La Niña conditions in the Pacific Ocean may amplify this process.

Although the sprites were in Kansas, Smith saw them from Oklahoma. This weather satellite image shows the observing geometry.

“I was about 200 miles away from the thunderstorm,” says Smith. Turns out, that’s about the right distance. You have to be far away to see sprites over the top of the thunderclouds.

Although sprites have been reported by pilots and storm chasers for more than a century, many scientists were skeptical. Can you blame them? “Doctor, I just saw a giant red jellyfish in the sky!” A turning point came in 1989 when sprites were photographed by researchers at the University of Minnesota and cameras onboard the space shuttle. Now sprites are in the mainstream. See for yourself.

Realtime Sprite Photo Gallery
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March 31, 2021: What a difference 20 years makes. Today the sun is blank and featureless as Solar Cycle 25 struggles pull solar activity from the doldrums of a deep Solar Minimum. In March 2001, however, the solar disk was peppered with sunspots, including a monster named “AR9393.” The biggest sunspot of Solar Cycle 23, AR9393 was a truly impressive sight, visible to the naked eye at sunset and crackling with X-class solar flares.

On March 29, 2001, AR9393 hurled a pair of CMEs directly toward Earth. The first one struck during the early hours of March 31, 2001. The leading edge of the shock front was dense (~150 protons/cc) and strongly magnetized — traits that give rise to powerful geomagnetic disturbances. Within hours, an extreme geomagnetic storm was underway, registering the maximum value of G5 on NOAA storm scales.

“I was fortunate to witness and photograph the event when I was just a teenager,” recalls Lukasz Gornisiewicz, who watched the show from Medicine Hat, Alberta:

In the hours that followed, Northern Lights spread as far south as Mexico. In 20 year old notes, Dr. Tony Phillips of Spaceweather.com describes “red and green auroras dancing for hours” over the Sierra Nevada mountains of California at latitude +37 degrees. Similar displays were seen in Houston, Texas; Denver Colorado; and San Diego, California.

“Here in Payson, Arizona, red curtains and green streamers were pulsating all across the sky,” wrote Dawn Schur when she submitted this picture to Spaceweather.com 20 years ago:

“We have seen some auroras here before, but this display was really special,” she wrote.

A second CME struck at ~2200 UT on March 31th. Instead of firing up the storm, however, the impact quenched it. When the CME passed Earth the interplanetary magnetic field surrounding our planet suddenly turned north — an unfavorable direction for geomagnetic activity.

Indeed, the quenching action of the second CME may have saved power grids and other technological systems from damage. The storm’s intensity (-Dst=367 nT) stopped just short of the famous March 14, 1989, event that caused the Quebec Blackout (-Dst=565 nT) and it was only a fraction of the powerful Carrington Event of 1859 (-Dst=~900 nT).

The whole episode lasted barely 24 hours, brief but intense. Visit Spaceweather.com archives for March 30, 31st and April 1, 2001, to re-live the event. Our photo gallery from 20 years ago is a must-see; almost all the pictures were taken on film!

March 30-31, 2001, Aurora Photo Gallery
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