Sept. 23, 2019: Could northern summer 2019 go down in history as “the summer without sunspots”? From June 21st until Sept 22nd, the sun was blank more than 89% of the time. During the entire season only 6 tiny sunspots briefly appeared, often fading so quickly that readers would complain to Spaceweather.com, “you’ve labeled a sunspot that doesn’t exist!” (No, it just disappeared.) Not a single significant solar flare was detected during this period of extreme quiet.

The sun on Sept. 22, 2019–as blank as a billiard ball. Credit: NASA/SDO

This is a sign that Solar Minimum is underway and probably near its deepest point. For 2019 overall (January through September), the sun has been blank 72% of the time, comparable to annual averages during the century-class Solar Minimum of 2008 (73%) and 2009 (71%). The current Solar Minimum appears to be century-class as well, meaning you have to go back to the beginning of the 20th century to find lulls in solar activity this deep.

Contrary to the sound of it, “Solar Minimum” is not boring. During this phase of the solar cycle, the sun’s magnetic field weakens, allowing cosmic rays to enter the solar system. This doses astronauts and possibly air travelers with extra radiation. The sun also dims, especially at extreme ultraviolet wavelengths, causing the upper atmosphere to cool and collapse. Space junk accumulates in Earth orbit as a result. Finally, streams of solar wind punch through the sun’s weakening magnetic field, lashing Earth with gaseous material that can cause geomagnetic storms. (One such stream is due later this week on Sept. 27-28.)

Interestingly, the summer of 2019 also brought us a sign that Solar Minimum is coming to an end. One of the numbered sunspots that briefly appeared on July 7th had a reversed magnetic polarity:

Above: A magnetic map of the sun’s surface (AR2744 inset) on July 7, 2019, from NASA’s Solar Dynamics Observatory

According to Hale’s Law, sunspots switch polarities from one solar cycle to the next. This small summertime sunspot was +/- instead of the usual -/+, marking it as a member of the next solar cycle, Solar Cycle 25. Solar Minimum won’t last forever!

Solar cycles always mix together at their boundaries. We can expect to see more new-cycle sunspots in the months ahead as Solar Cycle 24 dies out and Solar Cycle 25 slowly comes to life. If forecasters are correct, the next Solar Maximum will be in full swing by 2023.

Sept. 11, 2019: Scott Tilley has an unusual hobby. He scans the skies for satellites where they shouldn’t be. Using an S-band receiver, the amateur radio operator has tracked many classified spacecraft orbiting Earth and famously found NASA’s IMAGE satellite when it woke up from the dead last year. This past weekend he bagged another one: GOES-13.

“This was quite a surprise,” says Tilley. “I thought GOES-13 was in a graveyard orbit–yet I found it quite active and wandering on Sept. 8th.”

GOES-13 is a NOAA weather satellite. It was retired in January 2018 after a storied 12-year career during which it monitored some of the most notorious weather events in recent U.S. history – including Hurricane Sandy in 2012 and the triple disaster of Hurricanes Harvey, Irma and Maria in 2018. The satellite also experienced significant space weather: In December 2006, GOES-13 observed a solar flare so intense it damaged its onboard Solar X-ray Imager.

When weather satellites are retired, they are typically steered into a high parking orbit for storage. GOES-13 was reportedly “parked” over longitude 60W. But that’s not where Tilley found it.

Above: GOES-13 S-band signals received by Scott Tilley on Sept. 8, 2019.

“It was drifting westward through longitude 135W,” he says. “As it was emitting strong radio signals it seemed to me it was going somewhere and with no public statements I could find about this it encouraged me to start an observing campaign.”

Tilley quickly focused his attention on the night of Sept. 9th when the satellite would drift through Earth’s shadow–essentially experiencing a solar eclipse. Would the solar powered satellite survive the blackout?

“Indeed it did,” reports Tilley. “Strong radio transmissions continued before, during and after the eclipse. GOES-13 still has a working battery.”

Above: GOES-13’s response to a solar eclipse, indicating what appears to be nominal battery operation.

This is significant, Tilley explains, because “satellite batteries are sometimes intentionally disconnected as part of their retirement process.  The idea is to ensure the battery doesn’t explode or do something else unwelcome after the system is shutdown and create unintentional space debris. In my mind, a good battery seals the notion that GOES-13 is operational.”

But what is the operation? Tilley suspects that GOES-13 may have been drafted by the US military. News reports earlier this year suggested that the US Air Force is interested in using retired weather satellites as observing platforms. Before GOES-13 was “retired,” its visual imaging system was still fully functioning.

“Only time will tell where GOES-13 ends up,” says Tilley. “But given the nature of these observations there is no doubt in my mind the spacecraft is alive and under intelligent control. The question is, who is the intelligence?”

For a fuller discussion of Tilley’s observations, check out his blog post.

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Sept. 5, 2019: Sky watchers are still sorting out all the things they saw during last weekend’s Labor Day geomagnetic storm.  Upon further review, not every light in the sky was the aurora borealis. There was also STEVE:

“Look at the mauve-colored plume. That’s STEVE,” says Alan Dyer, who took the picture at the Saskatchewan Summer Star Party on Aug. 31st. “We saw STEVE two nights in a row from our area in western Canada.”

STEVE (Strong Thermal Emission Velocity Enhancement) looks like an aurora, but it is not. The phenomenon is caused by hot (3000°C) ribbons of gas flowing through Earth’s magnetosphere at speeds exceeding 6 km/s (13,000 mph). These ribbons appear during some geomagnetic storms, revealing themselves by their soft purple glow.

Earlier this year, researchers led by Toshi Nishimura of Boston University published an important paper about STEVE. Using data from NASA’s THEMIS spacecraft, they located STEVE’s power source: Magnetic explosions called ‘substorms‘ more than 22,000 km above Earth’s surface hurl streams of hot plasma toward Earth. When the material reaches an altitude ~250 km above Earth’s surface, it begins to emit a mauve light.

There’s more. THEMIS data showed that the same explosions can spray energetic electrons toward Earth. These electrons move even deeper into the atmosphere, all the way down to 100 km, where they ignite a form of green auroras called “the picket fence.” Indeed, many sky watchers saw the picket fence beneath STEVE over Labor Day weekend:

“STEVE and the green pickets were quite strong underneath the handle of the Big Dipper,” says Philip Granrud, who took the picture from Kalispell, Montana, on Sept. 1st. “It was beautiful!”

Nishimura’s study showed that STEVE and the green pickets are inextricably connected. “They are two different manifestations of a single magnetic explosion high above Earth,” explains Nishimura. “The picket fence is an aurora. STEVE is not. Nevertheless, they are linked.”

The colors of the display are only partially understood. Picket fences are green because of oxygen, which emits green photons when it is pummeled by energetic electrons. The purple color of STEVE … is still a mystery. “We are looking at this more closely in a follow-up study,” says Nishimura. “We suspect that nitrogen is involved, but we are not yet certain.”

Ready for more? Good news. The season for STEVE is now. Studies show that STEVE tends to occur more frequently during spring and fall than summer and winter. The onset of northern autumn, only weeks away, seems to lure the arc out of summer hiding. Stay tuned.  Aurora alerts: SMS Text

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Sept. 3, 2019: It happened just as predicted. On August 31st, a stream of solar wind hit Earth’s magnetic field, sparking the strongest geomagnetic storm of 2019. Episodes of G2-class storming ignited bright auroras over both poles visible even in Arctic twilight. Dmitry Rak photographed the display from  the Barents Sea coast near Teriberka, Russia:

“The aurora borealis mixed with the colors of sunset and dawn as the storm lasted the whole night of Aug. 31st to Sept. 1st,” reports Rak. “The most delicious auroras floated over us and headed south, so we were able to capture only part of this celestial extravaganza. Nevertheless, we were very satisfied with what we saw.”

Thousands of miles away in Wyoming, the sky and the ground both exploded:

“I got several images of the auroras over the geysers in Yellowstone National Park,” says photographer Jean Clark. “What a great night!”

At the peak of the storm, which lasted throughout the Labor Day weekend, auroras spilled across the Canadian border into multiple US states including Wisconsin, Michigan, Montana, Wyoming, Idaho, Maine and even Midwestern airspace.

Did you miss the show? The same stream of solar wind will return on Sept. 27th when the sun has spun once on its axis, directing the gaseous firehose at Earth again. Mark your calendar! Aurora alerts: SMS Text

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August 30, 2019: You never know what you might see in the wake of a big storm. On Aug. 25th, Chinese astrophotographer Chao Shen of Shaoxing City went outside to photograph the Milky Way. A typhoon named “White Deer” had passed through the day before, and the storm clouds were parting. “I saw the stars–but that’s not all,” says Shen. “A Gigantic Jet leaped up right before my eyes!”

Gigantic Jets are lightning-like discharges that spring from the tops of thunderstorms, reaching all the way to the edge of space. They’re related to sprites, but larger and more powerful.

“Shen definitely caught a Gigantic Jet,” confirms Oscar van der Velde of the Lightning Research Group at the Universitat Politècnica de Catalunya. “It looks like it may have reached as high as 90 km above the ground.”

“Gigantic Jets are much more rare than sprites,” says van der Velde. “While sprites were discovered in 1989 and have since been photographed by the thousands, it was not until 2001-2002 that Gigantic Jets were first recorded from Puerto Rico and Taiwan.” Only dozens of Gigantic Jets have ever been photographed.

Shen says that “the Jet came from a storm about 100 km southwest of me. It was so huge, I was able to see it clearly despite the distance.”

Above: The arrow in this weather map points from Chao Shen’s camera toward the jet-producing storm.

Observers of sprites may be wondering if Shen really saw this jet. The answer is “yes.” Unlike sprites, which flicker so rapidly that they are difficult to see with the unaided eye. Gigantic Jets can lasts for hundreds of milliseconds, long enough for human eyes to register their purple glow.

Gigantic jets are part of a growing menagerie of strange forms that appear above intense thunderstorms, including sprites, elves, trolls, and blue jets. Some researchers believe that cosmic rays help trigger these “transient luminous events” by ionizing the air in and around thunderheads. If so, now is a good time to look for Gigantic Jets, because cosmic rays are nearing a Space Age high. Thank you, Solar Minimum!

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