Noctilucent Clouds are Missing

Dec. 28, 2020: Something strange is happening 50 miles above Antarctica. Or rather, not happening.┬áNoctilucent 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 Spaceweather.com.

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 1.5┬║ 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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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!