A Warning from History: The Carrington Event Was Not Unique
August 30, 2020 September 1, 2020 / Dr.Tony Phillips	/ 7 Comments
Sept. 1, 2020: On Sept. 1st, 1859, the most ferocious solar storm in recorded history engulfed our planet. It was "the Carrington Event," named after British scientist Richard Carrington, who witnessed the flare that started it. The storm rocked Earth's magnetic field, sparked auroras over Cuba, the Bahamas and Hawaii, set fire to telegraph stations, and wrote itself into history books as the Biggest. Solar. Storm. Ever.
But, sometimes, what you read in history books is wrong.
"The Carrington Event was not unique," says Hisashi Hayakawa of Japan's Nagoya University, whose recent study of solar storms has uncovered other events of comparable intensity. "While the Carrington Event has long been considered a once‐in‐a‐century catastrophe, historical observations warn us that this may be something that occurs much more frequently."
Drawings of the Carrington sunspot by Richard Carrington on Sept. 1, 1859, and (inset) Heinrich Schwabe on Aug. 27, 1859. [Ref]
To generations of space weather forecasters who learned in school that the Carrington Event was one of a kind, these are unsettling thoughts. Modern technology is far more vulnerable to solar storms than 19th-century telegraphs. Think about GPS, the internet, and transcontinental power grids that can carry geomagnetic storm surges from coast to coast in a matter of minutes. A modern-day Carrington Event could cause widespread power outages along with disruptions to navigation, air travel, banking, and all forms of digital communication.
Many previous studies of solar superstorms leaned heavily on Western Hemisphere accounts, omitting data from the Eastern Hemisphere. This skewed perceptions of the Carrington Event, highlighting its importance while causing other superstorms to be overlooked.
A good example is the great storm of mid-September 1770, when extremely bright red auroras blanketed Japan and parts of China. Captain Cook himself saw the display from near Timor Island, south of Indonesia. Hayakawa and colleagues recently found drawings of the instigating sunspot, and it is twice the size of the Carrington sunspot group. Paintings, dairy entries, and other newfound records, especially from China, depict some of the lowest-latitude auroras ever, spread over a period of 9 days.
An eyewitness sketch of red auroras over Japan in mid-September 1770. [Ref]
"We conclude that the 1770 magnetic storm was comparable to the Carrington Event, at least in terms of auroral visibility," wrote Hayakawa and colleagues in a 2017 Astrophysical Journal Letter. Moreover, "the duration of the storm activity was much longer than usual."
Hayakawa's team has delved into the history of other storms as well, examining Japanese diaries, Chinese and Korean government records, archives of the Russian Central Observatory, and log-books from ships at sea–all helping to form a more complete picture of events.
They found that superstorms in February 1872 and May 1921 were also comparable to the Carrington Event, with similar magnetic amplitudes and widespread auroras. Two more storms are nipping at Carrington's heels: The Quebec Blackout of March 13, 1989, and an unnamed storm on Sept. 25, 1909, were only a factor of ~2 less intense. (Check Table 1 of Hayakawa et al's 2019 paper for details.)
Oriental reports of a giant naked-eye sunspot group (left) and auroras (right) in Feb. 1872. [Ref]
Contextualizing the Carrington Event has become a busy niche in space weather research. One team led by Jeff Love of the USGS recently confirmed the near equality of Carrington to the May 1921 superstorm. And Hayakawa's team has just unearthed new records of extreme auroras in South America.
Are we overdue for another Carrington Event? Maybe. In fact, we might have just missed one.
In July 2012, NASA and European spacecraft watched an extreme solar storm erupt from the sun and narrowly miss Earth. "If it had hit, we would still be picking up the pieces," announced Daniel Baker of the University of Colorado at a NOAA Space Weather Workshop 2 years later. "It might have been stronger than the Carrington Event itself."
History books, let the re-write begin.
Spiral Lights on Mars
August 23, 2020 August 26, 2020 / Dr.Tony Phillips	/ 1 Comment
August 25, 2020: NASA's MAVEN spacecraft has discovered something unexpected on Mars–and researchers are struggling to explain it.
"There is a vast spiral of ultraviolet light over Mars' South Pole," says Nick Schneider of the University of Colorado's Laboratory for Atmospheric and Space Physics. "We understand the origin of the light, but its shape is a mystery."
Shown in false-color (green), a spiral of UV light is swirling around the Martian South Pole.
The light is "nightglow." We have it here on Earth, too, where it's called "airglow." During the day, ultraviolet radiation from the sun breaks apart compounds in the upper atmosphere. At night, the atoms reassemble, glowing as they put themselves back together again. On Earth, airglow looks like the aurora borealis; people can actually see it. On Mars, the emission is ultraviolet, invisible to the human eye.
MAVEN has been monitoring Martian nightglow for years, yet the spiral pattern was only recently recognized. Schneider recalls the 'Eureka moment': "We were preparing a demo on our lab's internal projection sphere (like Science on a Sphere), which turned out to be the first time we had plotted the UV glow in polar coordinates. The spiral 'popped' and we were all quite giddy."
The chemistry of Martian nightglow. Nitric oxide (NO) also produces airglow on Earth.
The spiral is just the tip of the iceberg; the whole planet is surrounded by pulsating patterns of nightglow. High above the North Pole of Mars there is a luminous blob that pulses exactly twice a day. And around the equator there are three more blobs, evenly spaced, pulsing three times a day. Only the South Pole has a spiral, and it pulses once a day.
"It's pretty complicated," says Schneider.
To make sense of it all, Schneider and colleagues "spun up" a general circulation model (GCM) of the Martian atmosphere. (This part of the work was led by Francisco González-Galindo at the Instituto Astrofísica Andalucía.) GCMs are computer programs that model planetary atmospheres. They're used all the time by weather forecasters on Earth, and planetary scientists have Martian versions as well, complete with accurate values for solar heating, winds, chemistry, cloud formation, and so on.
According to the GCM, nightglow on Mars is shaped by atmospheric tides. The gravity of the sun pulls on the Martian atmosphere, and the atmosphere has a natural response: It essentially rings like a bell three times a day. This accounts for the pulsating blobs around the equator.
Figure 6 of Schneider et al's recent paper compares MAVEN data (panels a and b) to a GCM model of Martian nightglow (panel c).
"We were really impressed that the Mars General Circulation Model reproduced the equatorial patterns so well," says Schneider. "The brightest spot hovers above the Martian prime meridian for months at a time, with two fainter spots placed on either side. Pulsating downdrafts at those locations boost the chemical reactions which give rise to nightglow."
The model did not, however, account for the spiral. "We've really struggled to explain it," he admits. "And however we might explain why a spiral should exist at the South Pole, we also need to explain why it should not exist at the North Pole!"
More data from MAVEN and updates to the Mars General Circulation Model might eventually provide an answer. For now, it remains a dizzying mystery.
Schneider et al's original research was just published in the August 6, 2020, edition of JGR Space Physics. Read it here.
Approaching Mars
August 22, 2020 / Dr.Tony Phillips	/ Leave a comment
Aug. 21, 2020: By the time you finish reading this sentence, you'll be 40 km closer to Mars.
Earth and Mars are converging for a close encounter this Fall, one of the best since 2003, and their separation is rapidly shrinking–negative 8 km/s as of Aug. 21st. You are literally approaching the Red Planet. Just this week the brightness of Mars surpassed that of Sirius, the brightest star in the sky. Suddenly, Mars is almost bright enough to see in daylight and an easy target for backyard telescopes.
"Here is one hour of Mars rotating," says amateur astronomer Maximilian Teodorescu of Magurele, Romania, who animated a sequence of photos taken Aug 18th using his 14-inch Newtonian:
"Lots of features are visible," he says. "Note how the southern polar ice cap has contracted and broken–a result of it being late springtime on that side of Mars."
The best is yet to come. By the night of closest approach on Oct. 6th (0.4149 AU), Mars will more than double in brightness again, outshining everything in the night sky except Venus and the Moon. Throughout this apparition, the south pole will remain tilted toward Earth, giving observers a good view of the breakup of the ice cap as Martian spring turns into summer.
Can't wait? Right now, a good time to look is just before daybreak when Mars is high in the southern sky. Keep watching as twilight creeps up the sky. The planet's burnt orange hue looks beautiful when surrounded by the day's first hint of morning blue: sky map.
Congratulations, you're now almost 500 km closer to the planet Mars.
Realtime Mars Photo Gallery
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A Slow-Motion Solar Flare and CME
August 17, 2020: You know an explosion is powerful when it lasts for two hours. Yesterday, Aug. 16th (1726 UT), a B1-class solar flare took even longer to unfold. The 2.5 hr blast sent a powerful shock wave rippling through the sun's atmosphere, shown here in a time-lapse movie from NASA's Solar Dynamics Observatory:
No sunspot was involved. The explosion occured in a spotless region of the sun's southern hemisphere. A magnetic filament snapped, hurling debris far and wide. Some of that debris formed the core of a coronal mass ejection (CME), which has escaped the sun and is now billowing into the Solar System.
Coronagraphs onboard the Solar and Heliospheric Observatory (SOHO) are tracking the CME:
Clearly, the storm cloud is not heading directly for Earth. However, NOAA models of the CME's trajectory suggest it could deliver a glancing blow to Earth's magnetic field on August 20th. Minor geomagnetic storms and high-latitude auroras are possible when the CME arrives. Stay tuned. Aurora alerts: SMS Text.
Realtime Space Weather Photo Gallery
Cosmic Rays and the Weakening Solar Cycle
August 18, 2020: Cosmic rays are bad–and they're going to get worse. That's the conclusion of a new study entitled "Galactic Cosmic Radiation in Interplanetary Space Through a Modern Secular Minimum" just published in the journal Space Weather.
"During the next solar cycle, we could see cosmic ray dose rates increase by as much as 75%," says lead author Fatemeh Rahmanifard of the University of New Hampshire's Space Science Center. "This will limit the amount of time astronauts can work safely in interplanetary space."
Cosmic rays are the bane of astronauts. They come from deep space, energetic particles hurled in all directions by supernova explosions and other violent events. No amount of spacecraft shielding can stop the most energetic cosmic rays, leaving astronauts exposed whenever they leave the Earth-Moon system.
Back in the 1990s, astronauts could travel through space for as much as 1000 days before they hit NASA safety limits on radiation exposure. Not anymore. According to the new research, cosmic rays could limit trips to as little as 290 days for 45-year old male astronauts, and 204 days for females. (Men and women have different limits because of unequal dangers to reproductive organs.)
Why are cosmic rays growing stronger? Blame the sun. The sun's magnetic field wraps the entire solar system in a protective bubble, normally shielding us from cosmic rays. In recent decades, however, that shield has been growing weaker–a result of the sputtering solar cycle.
The sunspot cycle has been trending weaker since the 1950s. The red curve is a prediction for upcoming Solar Cycle 25. [More]
Solar activity isn't what it used to be. In the 1950s through 1990s, the sun routinely produced intense Solar Maxima with lots of sunspots and strong solar magnetic fields. Now look at the plot, above. Since the heyday of the late 20th century, the 11-year solar cycle has weakened, and the sun's magnetic field has weakened with it.
Rahmanifard and colleagues believe we could be entering a Grand Minimum–a long, slow dampening of the 11-year solar cycle, which can suppress sunspot counts for decades. The most famous example of a Grand Minimum is the Maunder Minimum of the 17th century when sunspots practically vanished for 70 years.
"We are not in a Maunder Minimum," stresses Rahmanifard. "The current situation more closely resembles the Dalton minimum of 1790-1830 or the Gleissberg minimum of 1890-1920." During those lesser Grand Minima, the solar cycle became weak, but didn't completely go away.
In these plots, Rahmanifard et al compare the Dalton and Gleissberg minima (top panels) to recent solar cycles (bottom panels).
For years, researchers have been monitoring cosmic rays using CRaTER, a sensor orbiting the Moon on board NASA's Lunar Reconnaissance Orbiter (LRO). Recent data show that cosmic rays are at very high levels–the highest since LRO was launched in 2009. (See Figure 1 in their paper.)
"We took the latest readings from CRaTER and extrapolated them forward into Solar Cycle 25 (the next solar cycle)," says Rahmanifard. "We found that radiation doses will probably exceed already-high values by 34% for a Gleissberg-like minimum to 75% for a Dalton-like minimum."
Study co-author Nathan Schwadron, also of the University of New Hampshire, wonders if NASA should rethink its safety limits to allow longer voyages. "Or," he suggests, "maybe we should wait, and only conduct long-duration missions during Solar Maximum when galactic cosmic radiation falls to lower levels."
For astronauts, it begs the question — How much can you get done in 200 days? Barring improvements in shielding technology, future space missions may be limited to only 6 or 7 months, probably too short for a Mars voyage. Lunar exploration could be safer because the body of the Moon itself blocks radiation. But in interplanetary space, the researchers caution, "the next decade or two may be more dangerous than previously realized."
Stay tuned for updates as Solar Cycle 25 unfolds.
Solar Cycle 25 is Coming to Life
August 4, 2020 / Dr.Tony Phillips	/ 3 Comments
August 3, 2020: There's no longer any doubt. New Solar Cycle 25 is coming to life. The latest sign came today with the emergence of a new sunspot group, AR2770, inset in this magnetic map of the sun's surface from NASA's Solar Dynamics Observatory (SDO):
In this false-color image of the sun, intense magnetic fields are denoted by yellow (- polarity) and green (+ polarity).
AR2770 has two dark cores (each about the size of Mars) and is crackling with minor B-class solar flares. Its potential for even stronger flares will become clear in the days ahead as the sunspot turns toward Earth, more fully revealing its magnetic complexity.
Active regions from Solar Cycle 25 are now strewn across the sun's northern hemisphere. These are places where magnetic fields are intensifying, creating islands of magnetism on the sun's surface.
The -/+ magnetic polarities of these northern active regions mark them as members of Solar Cycle 25, per Hale's Law.
In the cases of AR2769 and AR2770, the fields have intensified enough to form dark cores–that is, sunspots. A few days ago, AR2768 also had visible sunspots. It's a target–rich environment for amateur astronomers with safe solar telescopes.
The appearance of so many active regions at once is a clear sign that Solar Cycle 25 is gaining steam. However, that doesn't mean Solar Minimum is finished. These are just "starter sunspots," pipsqueaks compared to the behemoths expected when Solar Cycle 25 reaches its peak a few years from now. Solar activity should remain generally low despite this uptick in sunspot counts.
On the other hand, even a starter sunspot can occasionally cause a very big storm–so stay tuned. Solar flare alerts: SMS Text.