Solar Tsunami and CME

Aug. 27, 2021: Sunspot AR2859 erupted on Aug. 26th, producing a C3-class solar flare: movie. The flare, however, was not the main attraction. The eruption also caused a massive “solar tsunami.” Watch the shadowy wave ripple across the sun in this false-color ultraviolet movie from NASA’s Solar Dynamics Observatory:

The expanding circular shadow is a wave of hot plasma and magnetism. Based on the time it took to reach the next sunspot, halfway around the sun, the tsunami was traveling faster than 110,000 mph.

Solar tsumanis always herald a CME, and this one was no exception. Soon after the tsunami broke, SOHO coronagraphs detected a plasma cloud leaving the sun: movie.

Update: NOAA analysts have modeled the CME’s trajectory. They predict an Earth impact during the late hours of Aug. 29th, possibly sparking G1-class geomagnetic storms through midday on Aug. 30th.   Aurora alerts: SMS Text.

SOLAR RADIO BURST: When sunspot AR2659 exploded on Aug. 26th, shortwave loudspeakers on the dayside of Earth erupted with static. “It was a solar radio burst,” reports Thomas Ashcraft, who recorded the sounds from his observatory in rural New Mexico. Click to listen:

Take another look at the “solar tsunami,” above. Much of the static Ashcraft recorded is caused by that shock wave rippling through the sun’s atmosphere. Plasma waves in the ionized corona naturally emit radio noise. Ham radio operators, military radar installations, and radio astronomers have been picking up these sounds since the 1940s. You can do it yourself from your own backyard.

“As I write, the sun just produced another very strong radio burst, which really packed a punch on my spectrograph!” says Ashcraft. In other words, stay tuned for more…

Perseid Meteor Outburst

Aug. 18, 2021: 28 years ago, the Perseid meteor shower killed a satellite. On Aug. 11, 1993, a Perseid meteoroid hit the Olympus-1 telecommunications satellite, making it spin. The $850 million spacecraft was lost after it ran out of fuel trying to regain control.  Many researchers blame a dense ribbon of comet dust now known as “the Perseid Filament.”

This week, the Perseid Filament came back. Probably.

Above: The Perseid outburst of Aug. 14, 2021, captured by Carl Bracken of the Cedar Amateur Astronomers in Iowa using his AMS42 camera. More images.

On Aug. 14, 2021, night skies over North America filled with meteors. P.  Martin of Ottawa, Canada, reported “multiple Perseids per minute with many bursts, sometimes 3-4 in a second.” In San Diego, Robert Lunsford of the International Meteor Organization also witnessed rapidfire streaks, 2 to 3 at a time. “It made me realize something unusual was going on,” Lunsford says, “especially so far from the predicted maximum.”

To say that astronomers were surprised would be an understatement. The Perseid’s annual peak had occurred the night before. Most observers had already given up watching. Fortunately, a network of automated cameras operated by the Cedar Amateur Astronomers in Iowa captured the display. Overnight they recorded almost 3000 meteors.

Above: Meteor rates during the 2021 outburst. More.

Peter Jenniskens, an astronomer at the SETI Institute and NASA/Ames, believes it may have been the Perseid Filament. “I think so,” he says. “The width of the outburst is similar to that of past Perseid Filament returns.”

The Perseid Filament is a ribbon of dust inside the broader Perseid debris zone. Comet 109P/Swift-Tuttle supplies the raw material. The comet loops around the sun every 133 years, shedding dust as it goes. Over time, much of Swift-Tuttle’s dust is perturbed by the gravity of Jupiter, helping scatter it into the diffuse cloud that we experience every year as the Perseid meteor shower. But there is a part of the comet’s orbit in a “mean motion resonance” with Jupiter where dust can accumulate instead of dispersing. This is the Perseid Filament.

Forecasters still can’t predict when the Perseid Filament will return. It came for many years in a row around 1993, and it may have grazed Earth again, slightly, in 2018, 2019 and 2020. No one predicted a direct hit in 2021.

This uncertainty naturally raises the question: Was it really the Filament? The jury’s still out. Observers may have stumbled upon an entirely new ribbon of Perseid dust. Either way, researchers are looking forward to next year to see if it comes back again. And they probably won’t stop watching when the peak is “done.”

Blue Lightning in the Stratosphere

Aug. 15, 2021: Rain. Clouds. Thunder. The stratosphere has none of those things. Weather up there is pretty dull. Except when the lightning starts….

Researchers call them “blue jets.” The elusive discharges leap into the stratosphere from thunderstorms far below. They are rarely seen, but storm chaser Rob Neep was able to capture some over Sonora, Mexico, on August 3rd:

“I couldn’t believe my eyes,” says Neep, a former TV photojournalist. “I was actually looking for sprites when the jets appeared. They were definitely visible to the naked eye, both my cousin and I observed them.”

Oscar van der Velde of the Lightning Research Group at the Universitat Politècnica de Catalunya watched Neep’s video and says it is “Excellent–perhaps the best example of classic blue jets we’ve seen in a long time!”

First recorded by cameras on the space shuttle in 1989, blue jets are part of a growing menagerie of transient luminous events (TLEs) in the upper atmosphere. They appear alongside sprites, ELVES, and other lightning-like forms. Blue jets, however, seem to be more elusive than the others, often frustrating photographers who try to catch them.

“We’re not sure why ground-based observers see them so rarely,” says van der Velde. “It might have something to do with their blue color. Earth’s atmosphere naturally scatters blue light, which makes them harder to see. Neep’s video was taken from a relatively high altitude site (elevation 3500 ft); thin clear air probably helped.”

“Not all storms have blue jets,” he allows. “Even so, blue jets may be much more common than we think.”

Above: Artist’s concept of a blue jet observed from the ISS. Credit: DTU Space, Daniel Schmelling/Mount Visual

In 2018, SpaceX launched Europe’s Atmosphere-Space Interactions Monitor (ASIM) to the International Space Station to study TLEs from space. Data from ASIM show that blue jets can leap as high as 170,000 feet above the ground. They’re sparked by mysterious “blue bangs“–brilliant blue flashes in the tops of thunderclouds possibly caused by intense turbulence.

It’s important to study blue jets because, according to van der Velde, “there can be considerable production of NOx and ozone by these discharges, potentially affecting the chemistry of the atmosphere.” Also, some blue jets might rise high enough to touch the ionosphere, forming a new and poorly understood branch of the global electrical circuit.

And on top of everything else, “they’re beautiful,” says Neep. “I was lucky to catch some.”

Rare Naked-Eye Nova

August 9, 2021: Every 20 years or so, a thermonuclear explosion occurs on the surface of RS Oph, a white dwarf in the constellation Ophiuchus. Yesterday, it happened again. On Aug. 8th, the brightness of the tiny star increased 600-fold, from magnitude +12 to +5. Keith Geary of Ireland was the first to notice. Hours later, Italian astronomer Ernesto Guido and colleagues photographed the outburst using a remote-controlled telescope in Australia:

This is called a “recurrent nova,” and it is rare. In the whole Milky Way galaxy, only 7 star systems are known to produce such explosions.

RS Oph is actually a binary star–a very lopsided one. On one side is a white dwarf, on the other is a red giant. There’s very little distance between the two, so the gravity of the white dwarf is able to pull gaseous material off the larger star down onto itself. Every couple of decades, enough matter accumulates to trigger an explosion. The last time this happened was back in 2006.

At 5th magnitude, the current outburst is visible to the unaided eye, albeit just barely. Binoculars or a telescope will allow you to see it with ease. Look south after sunset. Ophiuchus hangs high in the sky just above the better known constellations Scorpius and Sagittarius. Sky maps: simple, detailed, really detailed.

Update: Variable star observer Filipp Romanov of Yuzhno-Morskoy, Russia, has just seen RS Oph and estimates that its magnitude has increased further to +4.6.

Solar Max Might Come a Year Early

Aug. 3, 2021: Solar Cycle 25 is heating up faster than expected. The latest sign may be found in sunspot counts from July 2021. Continuing a trend that started last year, they overperform the official forecast:

Issued by the NOAA/NASA Solar Cycle 25 Prediction Panel in 2019, the official forecast calls for Solar Cycle 25 to peak in July 2025. However, a better fit to current data shows Solar Cycle 25 peaking in October 2024. This is just outside the 8-month error bars of the Panel’s forecast.

July 2021 was a remarkable month. Solar Cycle 25 crossed multiple thresholds, including its first X-flare and, at one point, 6 sunspots on the solar disk. The last time so many sunspots were seen at the same time was Sept. 2017 (SWx archive). One farside CME in July was so strong it affected Earth despite being on the “wrong” side of the sun. A handful of other CMEs narrowly missed our planet.

If solar activity increases apace, some of those blows will soon begin to land. Stay tuned.