Noctilucent Clouds over Argentina

Jan. 8, 2021: They’re back. Noctilucent clouds (NLCs), recently missing, are once again circling the South Pole. And, in an unexpected twist, they’ve just appeared over Argentina as well.

“This is a very rare event,” reports Gerd Baumgarten of Germany’s Leibniz-Institute of Atmospheric Physics, whose automated cameras caught the meteoritic clouds rippling over Rio Grande, Argentina (53.8S) on Jan. 3rd:

A second camera recorded the clouds at even higher latitude: Rio Gallegos (51.6S). At this time of year, noctilucent clouds are supposed to be confined to the Antarctic–not Argentina. In the whole history of atmospheric research, NLCs have been sighted at mid-southern latitudes only a handful of times.

“Personally, I am thrilled to see NLCs in Argentina, as I had not expected them to occur so far north,” says Natalie Kaifler of the German Aerospace Center (DLR), who operates a lidar (laser radar) alongside one of Baumgarten’s cameras.

Kaifler’s lidar “pinged” the clouds during the display and confirmed that they are genuine NLCs. Echoes pinpointed their altitude more than 80 km above Earth’s surface:

Above: The ~hour-long oscillations in these lidar echoes may be caused by gravity waves propagating upward from the Andes 82 km below.

NLCs are Earth’s highest clouds. They form when summertime wisps of water vapor rise up from the poles to the edge of space. Water crystallizing around specks of meteor dust ~83 km above Earth’s surface create beautiful electric-blue structures, typically visible from November to February in the south, and May to August in the north.

This season has been unusual, though. The normal onset of NLCs over the South Pole has been delayed for more than a month as strange weather patterns played out above Antarctica. Now, suddenly, they’re back, and showing up in unexpected places.

Baumgarten has set up two cameras in southern Argentina to catch unexpected NLCs. “If it happens again,” he says, “we’ll let you know.” Stay tuned!

Noctilucent Clouds are Missing

Dec. 28, 2020: Something strange is happening 50 miles above Antarctica. Or rather, not happening. Noctilucent clouds (NLCs), which normally blanket the frozen continent in December, are almost completely missing. These images from NASA’s AIM spacecraft compare Christmas Eve 2019 with Christmas Eve 2020:

“The comparison really is astounding,” says Cora Randall of the University of Colorado’s Laboratory for Atmospheric and Space Physics. “Noctilucent cloud frequencies are close to zero this year.”

NLCs are Earth’s highest clouds. They form when summertime wisps of water vapor rise up from the poles to the edge of space. Water crystallizing around specks of meteor dust 83 km (~50 miles) above Earth’s surface creates beautiful electric-blue structures, typically visible from November to February in the south, and May to August in the north.

A crucial point: Noctilucent clouds form during summer. And that’s the problem. Although summer officially started in Antarctica one week ago, the southern stratosphere still seems to think it’s winter. In particular, the stratospheric polar vortex, which should be breaking up around now, is stubbornly hanging on. The polar vortex chokes off gravity waves, which would normally carry water vapor into the upper atmosphere. Without water vapor, NLCs cannot form.

Above: These plots of ozone hole size and zonal wind speed highlight unusual conditions in the southern stratosphere in Dec. 2020.

“The southern hemisphere stratosphere is very unusual this year,” says Randall. “The ozone hole is exceptionally large, until recently zonal winds have been blowing in the wrong direction, and overall the stratosphere is much more ‘winter-like’ than it should be in December.”

Eventually, the stratosphere will shift into its summer-like state, and NLCs can begin to blossom. But when? Researchers don’t know. If the clouds remain suppressed only one more week, it will break previous records of low NLC activity in the southern hemisphere. Stay tuned for updates right here on

UPDATE: How do you make noctilucent clouds appear? Publish a story called “Noctilucent Clouds are Missing.” Hours after publication of this news item, NASA’s AIM satellite reported an uptick of NLC activity over Antarctica. “It’s still nowhere as many clouds as last year, but it makes sense given the recent steep drop in zonal wind speed and ozone hole area,” notes Randall. “The atmosphere definitely has a mind of its own this season!”

Weak Impact: The CME That Failed

Dec. 10, 2020: As predicted, a CME (pictured below) hit Earth’s magnetic field during the early hours of Dec. 10th (1:30 UT), but the impact did not cause a geomagnetic storm. Why not? Scroll down for the answer:

Why didn’t the CME cause a storm? Every CME brings with it some magnetic field from the sun. If that magnetic field points south, it opens cracks in Earth’s magnetic field, allowing solar wind to flow inside and fuel auroras. On the other hand, if the CME’s magnetic field points north, it seals cracks in Earth’s magnetic field, blocking the solar wind and quenching storms.

This CME brought a storm-killing north magnetic field. So, even though the velocity of the solar wind in the CME’s wake flirted with a high value of 600 km/s, it was ineffective at causing geomagnetic storms and auroras.

Maybe next time. Solar activity is picking up with the onset of new Solar Cycle 25. This is just the first of many CMEs likely to head our way in the months ahead. Aurora alerts: SMS Text.

Great Conjunction of Jupiter and Saturn

Dec. 7, 2020: Something special is happening in the sunset sky. It’s a Great Conjunction of Jupiter and Saturn. The two giant planets are converging for a close encounter the likes of which have not been seen since the Middle Ages. Shahrin Ahmad of Kuala Lumpur, Malaysia, photographed the pair on Dec. 7th:

“Jupiter and Saturn are about 1.5º apart this evening, ” says Ahmad. “Even under a light polluted sky, both can easily be seen.”

They’re about to get much closer. On Dec. 21st, the two planets will lie just 0.1 degrees apart. That’s so close, some people will perceive them as a single brilliant star. Viewed through binoculars or a small telescope, ringed Saturn will appear as close to Jupiter as some of Jupiter’s moons:

Although Great Conjunctions between Jupiter and Saturn occur every 20 years, they’re not all easy to see. Often the two planets are hidden in the glare of the sun. This year is special because the conjunction happens comfortably away from the sun. In fact, the last time the two worlds were so close together *and* so easy to see was the year 1226, astronomer Michael Brown told the Washington Post.

The show is underway. Jupiter and Saturn are already a tight pair in the evening sky, and they will grow rapidly and noticeably closer together every night for the next two weeks. Dates of special interest include Dec. 16th and 17th, when the crescent Moon joins the planets, and, of course, Dec. 21st when they are almost touching. Sky maps: Dec. 16, 17; Dec. 21.

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The Lopsided Solar Cycle

Dec. 5, 2020: Solar physicists have long known that the two hemispheres of the sun don’t always operate in sync.  While one hemisphere is active, the other may be utterly quiet; Solar Max in the North can be offset from Solar Max in the South by as much as two years. The sun’s lopsided behavior is on display right now, as shown in this Dec. 4th photo from NASA’s Solar Dynamics Observatory:

In the southern hemisphere, there are 4 times more active regions than in the north. Since the big sunspots of Solar Cycle 25 started appearing in October 2020, approximately 82% of all ‘spots have been in the south. The vast majority of all solar activity is coming from just one half of the sun.

An excellent historical review of sunspot activity penned by retired NASA scientist David Hathaway shows that solar cycles often tilt one way or the other. The great Solar Cycle 19 of the 1960s, for instance, was mostly southern, an asymmetry which spilled over into Solar Cycle 20 as well:

Above: Smoothed monthly sunspot areas for northern and southern hemispheres separately. The difference between the curves is filled in red if north dominates or blue if south dominates.

Smoothed monthly sunspot areas for northern and southern hemispheres separately. The difference between the curves is filled in red if north dominates or blue if south dominates.

Other solar cycles have been more balanced, with only razor-thin margins separating one hemisphere from the other.

How will Solar Cycle 25 shape up? If history is any guide, the northern hemisphere of the sun will eventually catch up. For now, though, Solar Cycle 25 has a distinctly southern personality. Solar flares, y’all?

Strange Antarctic Weather Extends to the Edge of Space

Dec. 2, 2020: Consider it the tip of the iceberg. Noctilucent clouds (NLCs) over the south pole are AWOL.

“Normally we see the first NLCs of the southern season around Nov. 21st,” says Cora Randall of the University of Colorado’s Laboratory for Atmospheric and Space Physics (LASP). “But this year, it’s already December and we’re still waiting.”

Above: What a different one year makes. NASA’s AIM spacecraft took these pictures of NLCs over Antarctica on Nov. 29, 2019 (left) and Nov. 29, 2020 (right)

Missing NLCs is just one of the curious weather patterns currently underway at the southern end of our planet.

Making a list: (1) Earth’s southern ozone hole is not only open, but also the biggest it’s ever been in December. (2)  The air above Antarctica is currently at record cold levels for this time of year–the result of an icy polar vortex that refuses to break up. (3) In the stratosphere, east-west winds at 60 degrees South are blowing at record speed. From top to bottom, the Antarctic atmosphere is in a quirky state.

Lynn Harvey, also at LASP, gathered these plots from the Goddard Space Flight Center showing some of the unusual meteorology:

Current conditions are circled in yellow. The ozone hole (left) and stratospheric winds (right) are both setting records for this time of year.

“Based on the trends, I would say noctilucent clouds might not appear until mid-December, which is pretty unusual,” says Harvey.

NLCs are Earth’s highest clouds. They form when summertime wisps of water vapor rise up from the poles to the edge of space. Water crystallizing around specks of meteor dust 83 km above Earth’s surface creates beautiful electric-blue structures, typically visible from November to February in the south, and May to August in the north. Their appearance over Antarctica in 2020 is now seriously overdue.

What’s causing the delay? “I would guess it’s ocean/atmosphere coupling,” speculates Randall. “La Nina strengthened in October, and this is known to affect large-scale circulation in the atmosphere (e.g., Butler et al., 2011; Lin & Qian, 2019).”

“It’s blowing the scale away this year,” says Hampton University professor James Russell, principal investigator for NASA’s AIM spacecraft, which monitors noctilucent clouds. “I can’t wait to see what happens next.”

Stay tuned!

Major Solar Flare and CME

Nov. 30, 2020: Yesterday (Nov. 29th at 1311UT), Earth-orbiting satellites detected the biggest solar flare in more than 3 years. NASA’s Solar Dynamics Observatory recorded this extreme-ultraviolet movie of the M4.4 category blast:

X-rays and UV radiation from the flare ionized the top of Earth’s atmosphere, producing a shortwave radio blackout over the South Atlantic: map. Ham radio operators and mariners may have noticed strange propagation effects at frequencies below 20 MHz, with some transmissions below 10 MHz completely extinquished.

Remarkably, this flare was even bigger than it seems. The blast site is located just behind the sun’s southeastern limb. As a result, the explosion was partially eclipsed by the body of the sun. It might have been an X-class event.

The flare also hurled a significant coronal mass ejection (CME) into space, shown here in a coronagraph movie from the Solar and Heliospheric Observatory (SOHO):

Update: At first it appeared that the CME would completely miss Earth. However, NOAA analysts believe that the outskirts of the cloud might deliver a glancing blow to Earth’s magnetic field on Dec. 1-2. If so, the impact could spark a minor G1-class geomagnetic storm with auroras over northern countries such as Canada, Iceland, Norway and Sweden.

It would be a different story if the main body of the CME hit. Then we would be anticipating a strong geomagnetic storm. Maybe next time!

“Next time” could be just days away. The hidden sunspot that produced this major event will rotate onto the Earthside of the sun during the next 24 hours or so. Then its ability to spark geomagnetic storms will be greatly increased. Instant solar flare alerts: SMS Text.

Little Green Cannonballs of Light

Nov. 22, 2020: Just when you thought STEVE couldn’t get any weirder. A new paper published in the journal AGU Advances reveals that the luminous purple ribbon we call “STEVE” is often accompanied by green cannonballs of light that streak through the atmosphere at 1000 mph.

“Citizen scientists have been photographing these green streaks for years,” says Joshua Semeter of Boston University, lead author of the study. “Now we’re beginning to understand what they are.”

STEVE is a recent discovery. It looks like an aurora, but it is not. The purple glow is caused by hot (3000 °C) rivers of gas flowing through Earth’s magnetosphere faster than 13,000 mph. This distinguishes it from auroras, which are ignited by energetic particles raining down from space. Canadian aurora watchers first called attention to the phenomenon about 10 years ago, whimsically naming it STEVE; researchers have been studying it ever since.

There’s a dawning realization that STEVE is more than just a purple ribbon. Photographers often catch it flowing over a sequence of vertical pillars known as the “picket fence.” They’re not auroras either. And, now, Semeter’s team has identified yet another curiosity in their paper, entitled “The Mysterious Green Streaks Below STEVE.”

“Beneath the picket fence, photographers often catch little horizontal streaks of green light,” explains Semeter. “This is what we studied in our paper.”

Semeter’s team gathered pictures of the streaks taken by citizen scientists in Canada, the United States and New Zealand. In some cases, the same streaks were photographed by widely-separated photographers, allowing a triangulation of their position. Analyzing dozens of high-quality images, the researchers came to these conclusions:

1. The streaks are not streaks. They are actually point-like balls of gas moving horizontally through the sky. In photos, the ‘green cannonballs’ are smeared into streaks by the exposure time of the cameras.

2. The cannonballs are typically 350 meters wide, and located about 105 km above Earth’s surface.

3. The color of the cannonballs is pure green–much moreso than ordinary green auroras, reinforcing the conclusion that they are different phenomena.

Above: The pure green of STEVE’s cannonballs (upper left) is compared to the blue-green and other mixed colors of auroras. Credit: Joshua Semeter, Boston University

So, what are the cannonballs? Semeter believes they are a sign of turbulence. “During strong geomagnetic storms, the plasma river that gives rise to STEVE flows at extreme supersonic velocities. Turbulent eddies and whirls dump some of their energy into the green cannonballs.”

This idea may explain their pure color. Auroras tend to be a mixture of hues caused by energetic particles raining down through the upper atmosphere. The ‘rain’ strikes atoms, ions, and molecules of oxygen and nitrogen over a wide range of altitudes. A hodge-podge of color naturally results from this chaotic process. STEVE’s cannonballs, on the other hand, are monochromatic. Local turbulence excites only oxygen atoms in a relatively small volume of space, producing a pure green at 557.7 nm; there is no mixture.

“It all seems to fit together, but we still have a lot to learn,” says Semeter. “Advancing this physics will benefit greatly from the continued involvement of citizen scientists.”

If you’re an aurora photographer looking to contribute, be sure to read Semeter et al’s original research at

Bright Comet Erasmus

Nov. 21, 2020: Every 2000 years, Comet Erasmus (C/2020 S3) visits the inner Solar System. News Flash: It’s back. Discovered on Sept. 17, 2020, by South African astronomer Nicolas Erasmus, the dirty snowball is plunging toward the sun for a close encounter inside the orbit of Mercury on Dec. 12th. This is what it looks like:

Gerald Rhemann took the picture Friday morning, Nov. 20th, using a 12-inch telescope in Farm Tivoli, Namibia. “The tail is magnificent,” he says. “In fact, I couldn’t fit it in a single field of view. This two-panel composite shows the first 3 degrees–and it keeps going well past the edge of the photo.”

Comet Erasmus is brightening as it approaches the sun. Right now it is 7th magnitude–an easy target for backyard telescopes. Forecasters believe it will more than triple in brightness to 5th magnitude by the time it dips inside the orbit of Mercury next month. Only the glare of the nearby sun will prevent it from being visible to the naked eye.

Where should you look? If you can find Venus, you can find the comet. Look low and southeast before sunrise. Comet Erasmus is in the constellation Hydra just to the right of Venus in neighboring Virgo. The bright star Spica is nearby, too, providing another useful reference point. Sky maps: Nov. 22, 23, 24, 25, 26.

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Suddenly, A Dark Streak Appears on Mars

Oct. 25, 2020: On Friday night, Oct. 22nd, longtime Mars photographer Maximilian Teodorescu of Magurele, Romania, looked at the Red Planet and noticed something he hadn’t seen before. “There is a dark streak in the Tharsis volcanic plateau,” he says. The mystery smudge is circled in these two images separated by about 40 minutes:

“The feature was not visible just a few nights ago when I photographed the same region,” says Teodorescu, who offers an Oct. 19th image for comparison. “Now, I have seen it two nights in a row (Oct. 22nd and 23rd), and other observers have seen it, too.”

What is it? Teodorescu’s first thought was “it must be some kind of cloud or streamer of dust.” Indeed, it is located in the same general area where a long icy cloud sometimes forms when wind whips around the summit of Arsia Mons, an extinct volcano.

To investigate further, Teodorescu projected the streak down onto a Mars Orbiter image of the region:

“The streak is about 600 km long,” he says. “It is close to Arsia Mons, but not a perfect match. Perhaps it is a shadow of the volcano’s ice cloud projected down onto lower Tharsis clouds.”

Mars photographers everywhere are encouraged to keep an eye out for this dark feature whenever the Tharsis volcanoes are facing Earth. Report your observations here, and we will share them.

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