Forbush Decrease: A Sudden Drop in Atmospheric Radiation

Dec. 3, 2021: Last month, a “Cannibal CME” hit Earth, sparking a strong G3-class geomagnetic storm and auroras as far south as California and New Mexico. You might think such a storm would boost radiation in Earth’s atmosphere. Think again. High-altitude balloons hurriedly launched by Earth to Sky Calculus during the storm on Nov. 3rd and 4th found just the opposite. Radiation in the stratosphere plummeted:

This is called a “Forbush decrease,” named after American physicist Scott Forbush who studied cosmic rays in the early 20th century.  It happens when a coronal mass ejection (CME) sweeps past Earth and pushes galactic cosmic rays away from our planet. Radiation from deep space that would normally pepper Earth’s upper atmosphere is briefly wiped out.

We have measured Forbush decreases before. For example, here’s one from Sept. 2014. The Forbush decrease of Nov. 3-4, 2021, was the deepest in the history of our 7-year atmospheric monitoring program. Radiation levels in the stratosphere over California dropped nearly 20%, more than doubling the previous record from our entire dataset.


Above: This is the CME that caused the Forbush decrease

This event illustrates the yin-yang relationship between solar activity and cosmic rays. As solar activity increases, more and more CMEs billow away from the sun, pushing cosmic rays out of the inner solar system. This is one reason we expect cosmic radiation to subside in the years ahead as young Solar Cycle 25 intensifies. Click here to learn more.

Andromedid Meteor Outburst

Nov. 29, 2021: The Andromedids are back. Over the weekend astronomers reported an outburst of more than 100 faint meteors per hour. “[It was] the strongest outburst of Andromedid meteors ever detected by the Canadian Meteor Orbit Radar (CMOR),” says Peter Brown of the University of Western Ontario. This radar sky map shows a hot spot of meteor activity on Nov. 28th:

The shower’s not over yet. “The current outburst is ongoing and it may be another few days or even a week before the activity ramps down,” says Brown. “These meteors are too faint to see with the naked eye, but they are easy targets for the radar.”

Andromedids are debris from Biela’s Comet, known to historians as “the comet that split in two.” 3D/Biela started to fall apart not long after it was discovered in 1772. It was a double comet when it swung by Earth in 1852, and was never seen again. In 1872 and 1885, thousands of meteors shot out of the constellation Andromeda as Earth passed through Biela’s remains. Chinese records described “stars that fell like rain.”

Above: Andromedids as seen on the night of November 27, 1872 by Amédée Guillemin (Le Ciel, notions d’astronomie, à l’usage des gens du monde et de la jeunesse, 1864 and 1877) [ref]

After that the Andromedids vanished, too. The shower has been weak or absent entirely since the late 19th century. Only a surprise outburst in 2011 signaled that Biela’s debris might still be lurking nearby. This week’s activity is even more promising.

Bill Cooke of NASA’s Meteoroid Environment Office (MEO) is one of several experts who have been modeling Biela’s debris streams, hoping to forecast a return. “Our models generally do not do well in predicting the timing or intensity,” he says. “However, this year our model got the timing roughly correct.” This plot shows current radar data (red dots) vs. predicted debris stream crossings:

According to Cooke’s model, the outburst on Nov. 28th was caused by a stream of dust laid down in 1655–interestingly before the comet fell apart. “We didn’t think the 1655 crossing would produce much of anything,” confesses Cooke. “So the outburst came as a bit of a surprise.”

A team of astronomers led by Paul Wiegert (including Brown) had already predicted a strong naked-eye Andromedid outburst in December 2023. If they are right, the display two years from now could yield as many as 200 bright meteors an hour, surpassing even the Perseids and Geminids. The current outburst is providing new data for their stream models, and could help improve the predictions.

Stay tuned for updates as the shower continues.

Note: The Canadian Meteor Orbit Radar is operated through a cooperative agreement between Western University’s Meteor Physics Group and NASA’s Meteoroid Environment Office.

Surprise: Some Red Auroras are *not* Auroras

Nov. 22, 2021: The biggest geomagnetic storm in years erupted this month when a Cannibal CME slammed into Earth’s magnetic field. Auroras spread as far south as California and New Mexico. Upon closer inspection, however, not all of those lights were auroras. Some were “SARs.”

SARs are pure red arcs of light that ripple across the sky during strong geomagnetic storms. Here’s an example from Finland in 2018:

“The SAR was visible to the naked eye for nearly 30 minutes and, after fading a bit, remained visible to my camera for another hour and a half,” recalls photographer Matti Helin.

On Nov 4, 2021, Earth experienced a veritable SAR storm. “We photographed SARs as far south as the McDonald Observatory in Texas,” reports Jeff Baumgardner of Boston University’s Center for Space Physics. “The bands of light swept over our cameras near Boston, then headed south. We knew something special was going on.”

SARs may look like auroras, but they not the same. Auroras appear when charged particles rain down from space, hitting the atmosphere and causing it to glow like the picture tube of an old color TV.  SARs form differently. They are a sign of heat energy leaking into the upper atmosphere from Earth’s ring current system.

During the storm on Nov. 4th, an all-sky camera in Capital Reef, Utah, caught a really bright one. Play the movie and watch what happens at the 18-second mark:

“It is pretty unusual to see an SAR at this low latitude,” says Asti Bhatt of SRI International. Bhatt operates MANGO, a continent-spanning network of cameras that monitors the sky for unusual phenomena like SARs.

SARs were discovered in 1956 at the beginning of the Space Age. Researchers didn’t know what they were and unwittingly gave them a misleading name: “Stable Auroral Red arcs” or SARs. In fact, SARs are neither stable nor auroras.

“Our group has observed  scores of SARs over the last three solar cycles,” says Baumgardner.  “In 2015 we published a paper describing them.  We found that SARs are ‘stable’ only when compared to very active auroras. When you watch an SAR for an hour or so, it can be quite dynamic.”

Space physicists are keen on SARs because they are linked to Earth’s ring current–a donut-shaped circuit carrying millions of amps around our planet. The ring current skims the orbits of geosynchronous satellites and plays a huge role in determining the severity of geomagnetic storms. Earth is the only rocky planet that has one.

Above: SARs photographed by the Dynamics Explorer-1 satellite in 1982. More

SARs are among the reddest things in the sky, with a monochromatic glow at 6300 Å that comes from atomic oxygen in the upper atmosphere. Unfortunately, the human eye is relatively insensitive to light at this wavelength. SARs are usually so faint that no one notices when they pass overhead. Cameras catch them easily, though. Pro tip for photographers: Use a 6300 Å filter.

“At the peak of a solar cycle we typically see 30 SARs per year near Boston,” says Baumgardner. “We hope this is a start of an active solar cycle with lots more SAR arcs!”

Space Weather and the Russian ASAT Strike

Nov. 16, 2021: Russia just destroyed one of its own satellites. On Nov. 15, 2021, a missile launched from the Plesetsk Cosmodrome struck Kosmos 1408, shattering the old satellite into thousands of pieces. Debris came so close to the ISS that astronauts took shelter in their crew capsules, just in case they had to abandon ship.

Littering Earth orbit with debris is never a good idea. Space weather could make it much worse. To understand why, turn back the clock 18 years to the Halloween Storms of October 2003, when our planet “lost” half its satellites.

Above: Northern Lights over Houston, Texas, on Oct. 29, 2003. Credit: Christie Ponder [photo gallery]

Solar Cycle 23 was winding down. Space weather forecasters were talking about how quiet things would soon become when, suddenly, the sun unleashed two of the strongest solar flares of the Space Age: An X17 flare on Oct. 28th followed by an X10 flare on Oct. 29th. Powerful CMEs struck Earth’s magnetic field only 19 hours later, sparking 3 days of severe to extreme geomagnetic storms.

An after action report from NOAA lists some of the storm’s side effects: Commercial airlines scrambled to redirect flights from the poles, where radiation levels were suddenly high. Each detour cost as much as $100,000. Many Earth-orbiting satellites experienced reboots and even unwanted thruster firings. Some operators simply gave up and turned their instruments off. Goddard’s Space Science Mission Operations Team estimates that 59% of NASA’s Earth and space science satellites were affected.

There’s a dawning awareness that something else important happened, too. Many of Earth’s satellites were misplaced.

In a 2020 paper entitled “Flying Through Uncertainty,” a team of researchers led by Thomas Berger at the University of Colorado’s Space Weather Technology, Research, and Education Center report a little-known anecdote from USAF satellite operators. During the Halloween storms, they recalled, “the majority of [low Earth orbiting] satellites were temporarily lost, requiring several days of around-the-clock work to reestablish [their positions].”

“The Halloween storms pumped an extra 3 Terrawatts of power into Earth’s upper atmosphere,” explains Martin Mlynczak, principal investigator of NASA’s SABER spacecraft, which measured the energy dump. “We didn’t feel it down on the planet’s surface, but it was a big event for Earth orbiting satellites. The extra power puffed up the atmosphere, sharply increasing aerodynamic drag.”

Above: A simulation of orbital position errors caused by a moderate geomagnetic storm for 2,653 objects in the USAF catalog. From “Flying Through Uncertainty.” [full caption]

Simulations show that even moderate geomagnetic storms can shift the position of a satellite by 10 km or more. The Halloween Storms created far larger uncertainties. This is a problem because, when you’re in a shooting gallery, you can’t dodge the bullets unless you know where they are.

“Fortunately, the Halloween storm did not cause any major collisions that we know of,” write Berger and his co-authors. “But if a geomagnetic storm on the level of the 2003 event were to occur today, the situation could be very different. Most satellite operators today have never experienced anything like the Halloween 2003 storm.”

Right now radars and telescopes in the United States Space Surveillance Network are surely working to pinpoint the debris of Kosmos 1408. Orbital solutions will allow collision warnings to be issued; satellites can dodge. However, a strong geomagnetic storm could wipe out their findings in an instant.

Intensifying geomagnetic activity is almost certain as young Solar Cycle 25 gains steam in the years ahead. It’s something to think about the next time you launch an ASAT weapon…

A Symphony of Magnetic Waves

Nov. 9, 2021: On Nov. 8th, for only a few hours, Earth’s magnetic field became very quiet. In the silence, a symphony ensued. Citizen scientist Rob Stammes recorded the performance using his magnetometer in Lofoten, Norway. “At first, the line on the digital chart recorder seemed flat,” he says, “but when I zoomed in I saw an almost musical superposition of sine waves.”

“This is very striking,” says Stammes, who has spent years observing and cataloging magnetic disturbances inside the Arctic Circle. “Note how the high-frequency Pc1 and Pc2 waves are superimposed on the slower Pc3. In musical terms, it’s a form of vibrato modulation.”

“Pc” stands for “pulsation continuous.” This is research jargon meaning, essentially, sine waves in the magnetosphere. They are present at all times, usually as a noisy cacophany of competing frequencies. Only during moments of extreme quiet can a few individual frequencies pop out and make music together.

Over the years, researchers have identified 5 types of Pc waves; Stammes recorded 3 of them. Fast Pc1 and Pc2 waves are associated with protons spiralling around Earth’s magnetic field. These waves scatter so-called “killer electrons” out of the Van Allen radiation belts, making space safer for satellites. Slower Pc3 waves are a gentle flutter caused by solar wind blowing down the flanks of the magnetosphere. (Imagine blowing across a piece of paper, making it flutter with your breath. Same idea.)

“Magnetic storms are great,” says Stammes, “but sometimes the ‘quiet’ can be just as interesting.”

Cannibal CME Sparks Low Latitude Auroras

Nov. 4, 2021: Auroras in California? Believe it. On Nov. 4th, the glow of a strong (G3) geomagnetic storm spread almost to Los Angeles. Aurora chaser Hongming Zheng took this picture just outside Lincoln CA at latitude +39N:

“This was my southernmost aurora sighting yet!” says Zheng. “A red glow and occasional pillars were visible to the naked eye. I was very pleasantly surprised with this unexpectedly strong geomagnetic storm.”

More reds appeared in Joshua Tree, California (+34N). “I could not see them with my naked eye,” says veteran observer Don Davis, “but my camera recorded these rare SoCal auroras.”

The CME that sparked the display was a special “Cannibal CME“–that is, a mashup of multiple solar storm clouds striking Earth all at once. Cannibal CMEs contain tangled magnetic fields and compressed plasmas that often do a good job sparking auroras.

At the apex of the storm, auroras appeared in New Mexico and Colorado as well–far below the latitudes where they usually appear.

In Abisko, Sweden, the auroras were so bright they could be seen at sunrise:

“I almost slept through the storm,” confesses photographer Oliver Wright. “I woke up just after 5am and I could see auroras through my bedroom window. So quick coffee and headed down to the bridge over the Abisko canyon. I was watching purple auroras getting washed out by the nautical sunrise. I’ve only ever seen that once before during the Saint Patrick Day geomagnetic storm of 2015.”

more aurora images:from Marianne Bergli of Tromsø, Norway; from Marybeth Kiczenski of Bayfield, Wisconsin; from Markus Varik of Tromsø, Norway; from Chris Cook of Cape Cod, Massachusetts; from Greg Ash of Duluth Minnesota; from Genevieve of Greenwood, Maine; from Thomas Spence of Tofte, Minnnesota; from Shelley Johnson of Anacortes, Washington

A CANNIBAL CME

Nov. 2, 2021: The CME heading for Earth is a cannibal. SOHO coronagraphs caught the storm cloud leaving the sun on Nov. 2nd following a slow-motion solar flare (M1.7) in the magnetic canopy of sunspot AR2891:

This CME is a cannibal because it ate others of its own kind. Cannibal CMEs are fast coronal mass ejections that sweep up slower CMEs in front of them. The mish-mash contains tangled magnetic fields and compressed plasmas that can do a good job sparking geomagnetic storms.

The slower CMEs, in this case, were hurled into space on Nov. 1st and 2nd by departing sunspot AR2887. The cannibal caught up with them almost immediately after leaving the sun. This NOAA computer model shows what happened:

The cannibal cloud swept up one whole CME and a portion of another. If NOAA’s model is correct, the combined CME will make first contact with our planet around 0600 UT on Nov. 4th. The model also predicts a +250 km/s increase in solar wind speed and a 6-fold jump in solar wind density in the CME’s wake. These conditions, if they materialize, would set the stage for geomagnetic storms as strong as category G2.

Subscribers to our Space Weather Alert Service will receive a text message when the CME arrives.

The Day Earth Lost Half Its Satellites (Halloween Storms 2003)

Oct. 29, 2021: Imagine waking up to this headline: “Half of Earth’s Satellites Lost!” Impossible?  It actually happened on an October day in 2003.

Turn back the clock 18 years. Solar Cycle 23 was winding down, and space weather forecasters were talking about how quiet things would soon become when, suddenly, the sun unleashed two of the strongest solar flares of the Space Age. The first, an X17-category blast on Oct. 28, 2003, hurled this CME directly toward Earth:

Above: A CME heading straight for Earth on Oct. 28, 2003. The source was an X17-flare in the magnetic canopy of giant sunspot 486. Image credit: SOHO. Movie

Traveling 2125 km/s (almost 5 million mph), the cloud slammed into Earth’s magnetic field only 19 hours later, sparking an extreme (G5) geomagnetic storm. The storm had barely begun when the sun erupted again. An X10-flare on Oct. 29th created another CME traveling almost as fast, 1948 km/s. It also arrived in 19 hours. The one-two punch kept the geomagnetic storms going for almost three full days–Oct. 29, 30, and 31, 2003.

Researchers named them “the Halloween Storms.” Modern accounts of the event tend to focus on auroras. Northern Lights descended as far south as Georgia, California, New Mexico, Arizona, Texas, and Oklahoma: photo gallery.

Above: Northern Lights over Houston, Texas, on Oct. 29, 2003. Credit: Christie Ponder [gallery]

But auroras were just the tip of the iceberg. High energy particles accelerated by the CMEs rifled toward Earth, peppering our planet’s atmosphere with protons and electrons. Onboard the International Space Station, astronauts took shelter in the hardened Zvezda service module. Hundreds of miles below, airline pilots were changing course. Almost every flight over Earth’s poles detoured to lower latitudes to avoid radiation, costing as much as $100,000 per flight. Many Earth-orbiting satellites experienced data outages, reboots and even unwanted thruster firings. Some operators simply gave up and turned their instruments off. Goddard’s Space Science Mission Operations Team estimates that 59% of NASA’s Earth and space science satellites were affected in one way or another.

There’s a dawning awareness that something else important happened, too. Many of Earth’s satellites were “lost.”

In a 2020 paper entitled “Flying Through Uncertainty,” a team of researchers led by Thomas Berger at the University of Colorado’s Space Weather Technology, Research, and Education Center report some little-known recollections from USAF satellite operators. During the Halloween storms, they recalled, “the majority of [low Earth orbiting] satellites were temporarily lost, requiring several days of around-the-clock work to reestablish [their positions].”

Above: Simulation of the effect of moderate geomagnetic storming on orbital position error as a function of altitude for 2,653 objects in the USAF catalog. From “Flying Through Uncertainty.” [full caption]

Satellites often go course during geomagnetic storms, but this was extreme.

“The Halloween storms pumped an extra 3 Terrawatts of power into Earth’s upper atmosphere1,” explains Martin Mlynczak, principal investigator of NASA’s SABER spacecraft, which measured the energy dump. “We didn’t feel it down on the planet’s surface, but it was a big event for Earth orbiting satellites. The extra power puffed up the atmosphere, sharply increasing aerodynamic drag.”

Simulations show that even moderate geomagnetic storms can shift the expected position of a satellite by 10 km or more. The Halloween storms created far larger uncertainties with the potential for collisions. United States Space Surveillance Network radars and telescopes worked urgently to find everything again.

Not knowing where satellites are is a problem mainly because of collisions. There are thousands of objects in Earth orbit ranging from billion-dollar active satellites to worthless nuts and bolts. Satellites are routinely maneuvered to avoid predicted collisions–but you can’t avoid a collision when you don’t know where you are.

“Fortunately, the Halloween storm did not cause any major collisions that we know of,” write Berger and his co-authors. “But if a geomagnetic storm on the level of the 2003 event were to occur today, the situation could be very different. Most satellite operators today have never experienced anything like the Halloween 2003 storm, and there are now (in 2020) more than 1,700 operational satellites and at least 19,400 pieces of debris larger than 10 cm in low Earth orbit.”

A number of countries and corporations are planning mega-constellations (Starlink is the most famous), which could ultimately swell the satellite population to 65,000 or more. Losing track of satellites in such a congested environment could theoretically trigger a cascade of collisions, rendering low Earth orbit unusable for years following an extreme geomagnetic storm.

Now that’s scary.

End notes:

  1. Martin Mlynczak provides some context:”While 3 Terawatts sounds like a lot of power (and it is!), averaged over the area of the Earth it is 6 milliwatts per square meter. The global average outgoing infrared radiation from the entire planet and atmosphere below 100 km is 240 watts per square meter.”
  2. For more information about the Halloween Storms, check out this excellent summary from NOAA.

Volcanic Comet 29P Erupts Again

Oct. 24, 2021:

The British Astronomical Association (BAA) is reporting another strong outburst of Comet 29P/Schwassmann-Wachmann. The volcanic comet suddenly brightened 10-fold on Oct. 23.75 UT when a sunlit vent opened, spewing ‘cryomagma’ into space. Dr. Richard Miles of the BAA provided this light curve:

Comet 29P is one of the strangest objects in the solar system. In fact, it strains the definition of “comet.” 29P is a ball of ice 60 km wide (much larger than a typical comet) trapped in a planet-like orbit between Jupiter and Saturn. It appears to be festooned with ice volcanoes which erupt ~20 times a year.

A rapidfire “super-eruption” of 4 volcanoes in late September created an expanding shell of vaporized cryomagma, which astronomers have been monitoring. Yesterday’s eruption propelled a new compact shell into the old larger one:

Above: Comet 29P photographed less than 12 hours after the Oct. 23rd eruption. Credit: Jean-Francois Soulier of France.

29P rotates once every ~58 days. As sunlight sweeps across its frozen surface, cryovolcanoes erupt under the high sun. “The latest eruption has taken place some 59 days after a similar event on August 25th, and may be an example of an outburst from the same cryovolcano erupting a second time on the next rotation of the nucleus,” says Miles.

Amateur astronomers with mid-sized telescopes and astrophotography experience are encouraged to monitor 29P. It changes every night. The comet is located in the constellation Auriga, high in the northern sky at midnight. Point your optics here and check the BAA’s Mission 29P website for updates.

more images: from Eliot Herman using a telescope in Mayhill, New Mexico

The Strange Magnetization of Sunspot AR2887

Oct. 24, 2021: Something does not add up. New sunspot AR2887 has two primary cores, each about the size of Earth. Usually when a sunspot looks like this, the two cores have opposite magnetic polarities, positive (+) and negative (-). In this case, however, they’re the same.

Pictured above is a magnetic map of AR2887 from NASA’s Solar Dynamics Observatory. It shows the primary poles of double sunspot AR2887 are both negative (-). Surrounding patches of positive (+) magnetic flux provide balance.

Perhaps AR2887 is not one but actually two sunspots jammed together in close proximity. We’ll get a better view of its magnetic architecture as AR2887 turns toward Earth in the days ahead. Stay tuned. Solar flare alerts: SMS Text.

more images: from Cai-Uso Wohler of Bispingen, Lueneburg Heath, Germany; from Francois Rouviere of Cannes, France; from Richard Jaworski of Carlingford, NSW, Australia; from Maximilian Teodorescu of Magurele, Romania;