May 31, 2019: A huge blue cloud of frosted meteor smoke is pinwheeling around the Arctic Circle. NASA’s AIM spacecraft spotted its formation on May 20th, and it has since circled the North Pole one and a half times, expanding in size more than 200-fold.

“These are noctilucent clouds,” says Cora Randall of the AIM science team at the University of Colorado. “And they are going strong.”

Noctilucent clouds (NLCs) in May are nothing unusual. They form every year around this time when the first wisps of summertime water vapor rise to the top of Earth’s atmosphere. Molecules of H₂O adhere to specks of meteor smoke, forming ice crystals 80 km above Earth’s surface. When sunbeams hit those crystals, they glow electric-blue.

But these NLCs are different. They’re unusually strong and congregated in a coherent spinning mass, instead of spreading as usual all across the polar cap.

“This is most likely a sign of planetary wave activity,” says Randall.

Planetary waves are enormous ripples of temperature and pressure that form in Earth’s atmosphere in response to Coriolis forces. They are responsible in part for undulations in the jet stream and can have a major influence on global weather. All rotating planets with atmospheres have these kind of waves.

Data from NASA’s Microwave Limb Sounder (MLS)  instruments show that, indeed, a planetary wave is circling the North Pole:

“The region of coldest temperatures migrates clockwise around the hemisphere, making one complete lap in about 5 days,” notes Lynn Harvey of the AIM science team who processed the data. “This is where the NLCs are forming.”

Because of planetary wave activity, the 2019 season is shaping up to be unusually good. The clouds have already made an appearance in the USA–something that usually doesn’t happen until late June or July.

“Last night, I took my dog out an hour and twenty minutes after sunset and was happily surprised to see these noctilucent clouds,” reports Shelley Johnson of Anacortes, Washington, who took this picture  on May 30th:

NLCs have also been sighted in Europe–highlighted by a bright display in Germany. “This is my earliest observation of noctilucent clouds and, considering the fact that it’s only May, they were exceptionally bright and well structured,” reports Laura Kranich of Kiel, Germany. “Seems like this is going to become a great season!”

If the 2019 NLC season continues to develop this quickly, even mid-latitude observers may soon be seeing this polar phenomenon. Observing tips: Look west 30 to 60 minutes after sunset when the sun has dipped below the horizon. If you see luminous blue-white tendrils spreading across the sky, you may have spotted a noctilucent cloud.

Realtime Noctilucent Cloud Photo Gallery

 

May 24, 2019: In November 2032, Earth will pass through the Taurid Swarm, a cloud of debris from Comet 2P/Encke that makes brilliant fireballs when its gravelly particles occasionally hit Earth’s atmosphere. Previous encounters with the Swarm in 2005 and 2015 produced showers of bright meteors observed around the world; in 1975 the Swarm contacted the Moon, making Apollo seismic sensors ring with evidence of objects hitting the lunar surface. If forecasters are correct, we’re in for similar activity 13 years from now.

Some researchers are beginning to wonder if there might be more to the Taurid Swarm than the pebble-sized particles that make fireballs–something, say, that could level a forest. On June 30, 1908, a forest in Siberia did fall down when a 100-meter object fell out of the sky and exploded just above the Tunguska River. Back-tracking the trajectory of the impactor suggests it may have come from the Taurid Swarm.

Above: Trees felled by the Tunguska explosion. Credit: the Leonid Kulik Expedition

Why would the Swarm contain such big rocks? After all, comet debris is normally no bigger than specks of dust. The most popular theory holds that 10 or 20 thousand years ago, a giant 100-km wide comet fragmented in the inner solar system. The breakup produced a mixture of dust and asteroid-sized bodies that are still present today. Comet 2P/Encke itself may be just one of the fragments.

If the Taurid Swarm does indeed contain Tunguska-class impactors, the people of Earth need to know. A team of astronomers from the University of Western Ontario (UWO) suggests that this summer is a great time to find out.

“In June 2019 the Earth will approach within [0.06 AU or 9 million km] of the center of the Taurid swarm, its closest post-perihelion encounter with Earth since 1975,” write UWO astronomers David Clark, Paul Wiegert and Peter Brown in a paper just accepted for publication in the Monthly Notices of the Royal Astronomical Society. “This will be the best viewing geometry to detect and place limits on the number of Near-Earth Objects proposed to reside at the swarm center until the early 2030s.”

To be clear, the team won’t be looking for fireballs disintegrating in Earth’s atmosphere. Instead, they want to point powerful telescopes at the Swarm, peering deep inside it to see if they can find big, dangerous pieces of rock gliding among the pebbles.

“Seeing anything in the Taurid Swarm will be tough,” says Wiegert. “It’s faint, it’s spread across a lot of sky, and it’s moving fast. A fair dash of serendipity will be needed to catch a glimpse of it. But we have to try to strike when the iron is hot, and that’s now.”

“We’ve applied for 10 hours of time on the Canada-France-Hawaii Telescope atop Mauna Kea,” he adds. “And we’re hoping other big telescopes will join the search as well.”

To learn more about this year’s close encounter with the Taurid Swarm, read the original research at https://arxiv.org/pdf/1905.01260.pdf

May 24, 2019: NASA’s AIM spacecraft has spotted wispy patches of electric-blue drifting over the Arctic Ocean. This marks the beginning of the 2019 season for noctilucent clouds (NLCs). The clouds are boxed in this polar image recorded by AIM’s CIPS instrument:

These first detections from space are mostly small and faint. They won’t remain faint for long, however. Previous data from AIM have shown that NLCs are like a great “geophysical light bulb.” They turn on every year in late spring, reaching almost full intensity over a period of 10 days. This means observers on the ground should soon begin to see them.

NLCs are Earth’s highest clouds. Seeded by meteoroids, they float at the edge of space more than 80 km above the planet’s surface. The clouds are very cold and filled with tiny ice crystals. When sunbeams hit those crystals, they glow electric-blue.

This is what a fully-realized noctilucent cloud looks like, photographed over the Lille Vildmose Wild Life Park in Denmark by Pernille Fjeldgaard Jensen on July 6, 2018:

Early-season NLCs are always found at high-latitudes–e.g., Canada, the British isles, Siberia and Scandinavia. To people in those areas, we offer the following observing tips: Look west 30 to 60 minutes after sunset when the sun has dipped below the horizon. If you see luminous blue-white tendrils spreading across the sky, you may have spotted a noctilucent cloud.

Realtime Noctilucent Cloud Photo Gallery

May 21, 2019: Every summer since the late 1970s, radars probing Earth’s upper atmosphere have detected strong echoes from altitudes between 80 km and 90 km. What’s up there? Noctilucent clouds (NLCs). NASA’s AIM spacecraft is still waiting to spot the first NLCs of the 2019 season, but the echoes have already begun. Rob Stammes of the Polarlightcenter in Lofoten, Norway, detected them on May 19th and 20th:

“I detected these VHF signals coming from transmitters in Eastern Europe,” he explains. “Before they reached my receiver in Norway, they bounced off something in the mesosphere. The patterns were recognizable and very strong.”

Researchers call them “Polar Mesospheric Summer Echoes” or “PMSEs.” They occur over the Arctic during the months of May through August, and over the Antarctic during the months of November through February. These are the same months that NLCs appear.

The underlying physics of these echoes is still uncertain. A leading theory holds that the ice particles in noctilucent clouds are electrically charged, and this makes them good reflectors of radio waves. However, NLCs are not always visible when the radar echoes are observed and vice versa.

The echoes Stammes detected suggest that the season for NLCs is about to begin.

“It certainly should be starting soon!” says Cora Randall of the AIM science team at the University of Colorado. “We’ve been looking at MLS temperature and water vapor data. As of last week, the north polar mesopause was colder and wetter than in any other years of the AIM record at this time.” In other words, conditions are ripe for water vapor to crystallize around meteor smoke, forming icy tendrils of electric-blue at the edge of space.

High-latitude sky watchers should be alert for their return. Observing tips: Look west 30 to 60 minutes after sunset when the sun has dipped 6^o to 16^o below the horizon. If you see luminous blue-white tendrils spreading across the sky, you may have spotted a noctilucent cloud.

Realtime Noctilucent Cloud Photo Gallery

 

May 20, 2019: Around the world, amateur astronomers are monitoring a strange phenomenon on the verge of Jupiter’s Great Red Spot (GRS). The giant storm appears to be unraveling. “I haven’t seen this before in my 17-or-so years of imaging Jupiter,” reports veteran observer Anthony Wesley of Australia, who photographed a streamer of gas detaching itself from the GRS on May 19th:

The plume of gas is enormous, stretching more than 10,000 km from the central storm to a nearby jet stream that appears to be carrying it away. Wesley says that such a streamer is peeling off every week or so.

The Great Red Spot is the biggest storm in the solar system–an anticyclone wider than Earth with winds blowing 350 mph. Astronomers have been observing it for hundreds of years. In recent decades, the Great Red Spot has been shrinking. Once it was wide enough to swallow three Earths; now only one of our planet could fit inside the maelstrom. This has led some researchers to wonder if the GRS could break up or disappear within our lifetimes. Perhaps the streamers are part of this process.

In fact, such unraveling clouds have been seen before. For instance, the Gemini North adaptive optics telescope on Maunakea saw a lesser but similar streamer in May of 2017:

The leader of those observations, Glenn Orton of NASA’s Jet Propulsion Laboratory, noted “a curious hook-like cloud feature on the Great Red Spot’s western side. Events like this show that there’s still much to learn about Jupiter’s atmosphere,” he said in a press release.

Wesley describes how the streamers are behaving now: “Each streamer appears to disconnect from the Great Red Spot and dissipate. Then, after about a week, a new streamer forms and the process repeats. You have to be lucky to catch it happening. Jupiter spins on its axis every 10 hours and the GRS is not always visible. A joint effort between many amateurs is underway to get clear images of the process.”

Indeed, now is a great time to monitor the action. Jupiter is approaching Earth for a close encounter in June 2019. During the weeks around opposition on June 10th, Jupiter will shine 4 times brighter than Sirius, the brightest star in the sky, and even small telescopes will reveal its storms, moons, and cloud belts.

Stay tuned for more unraveling.

May 13, 2019: Three and possibly four CMEs are en route to Earth following a series of explosions near sunspot AR2741. The most potent so far occurred on May 12th when a filament of magnetism surrounding the sunspot became unstable and erupted. The blast zone was more than 220,000 km in diameter:

Similar eruptions on May 10th, 11th and 13th combined with this one to produce a train of faint coronal mass ejections (CMEs) heading in our direction. The incoming CMEs are lightweights compared to the bright massive CMEs typically seen during Solar Maximum. However, their combined effect could rattle Earth’s magnetic field.

NOAA forecasters estimate a 55% to 60% chance of G1-class geomagnetic storms on May 15th and 16th. Isolated periods of even stronger G2-class storms are possible as well. Aurora Alerts: SMS Text.

Realtime Aurora Photo Gallery

May 11, 2019: Northern Lights are usually green, sometimes red. Those are the colors we see when oxygen is hit by electrons raining down from space during a geomagnetic storm. On Friday night, however, Harlan Thomas of Calgary, Alberta, witnessed a different color: deep-blue.

“To see these incredible blue pillars was out of this world,” says Thomas.

In auroras, blue is a sign of nitrogen. Energetic particles striking ionized molecular nitrogen (N2+) at very high altitudes can produce a blue glow rarely seen during auroral displays. In this case, it was the afterglow of a CME impact.

The CME left the sun on May 6th, propelled in our direction by an explosion in the magnetic canopy of sunspot AR2740. When it finally arrived on May 10th, the slow-moving storm cloud rattled Earth’s magnetic field, triggering a minor G1-class geomagnetic storm. Auroras were sighted in parts of Canada as well as US States such as Michigan and Minnesota.

“To top it off, STEVE appeared for several minutes as well,” says Thomas, who captured it in this shot:

STEVE is a hot (3000 degrees C) ribbon of ionized gas slicing through Earth’s upper atmosphere some 300 km above the ground. It appears unpredictably during some, but not all, geomagnetic storms. Originally thought to be a form of aurora borealis, new research shows that it is not an aurora at all.

The soft purple color of STEVE may also be caused by emissions from nitrogen, according to a new study just published in the Geophysical Research Letters. Coincidence? STEVE and blue auroras seem to share a connection to the 7th element on the periodic table.

Blue auroras are most often seen during intense geomagnetic storms–yet this was a relatively minor storm. Why nitrogen-blue overtopped the usual hues of oxygen on May 11th is unclear. It just goes to show, auroras still have the capacity to surprise. Aurora Alerts: SMS Text.

Realtime Aurora Photo Gallery