What if … A Perfect CME Hit Earth?

Jan. 21, 2021: You’ve heard of a “perfect storm.” But what about a perfect solar storm? A new study just published in the research journal Space Weather considers what might happen if a worst-case coronal mass ejection (CME) hit Earth. Spoiler alert: You might need a backup generator.

For years, researchers have been wondering, what’s the worst the sun could do? In 2014, Bruce Tsurutani (JPL) and Gurbax Lakhina (Indian Institute of Geomagnetism) introduced the “Perfect CME.” It would be fast, leaving the sun around 3,000 km/s, and aimed directly at Earth. Moreover, it would follow another CME, which would clear the path in front of it, allowing the storm cloud to hit Earth with maximum force.

None of this is fantasy. The Solar and Heliospheric Observatory (SOHO) has observed CMEs leaving the sun at speeds up to 3,000 km/s. And there are many documented cases of one CME clearing the way for another. Perfect CMEs are real.

Using simple calculations, Tsurutani and Lakhina showed that a Perfect CME would reach Earth in only 12 hours, allowing emergency managers little time to prepare, and slam into our magnetosphere at 45 times the local speed of sound. In response to such a shock, there would be a geomagnetic storm perhaps twice as strong as the Carrington Event of 1859. Power grids, GPS and other high-tech services could experience significant outages.

Sounds bad? Turns out it could be worse.

In 2020, a team of researchers led by physicist Dan Welling of the University of Texas at Arlington took a fresh look at Tsurutani and Lakhina’s Perfect CME. Space weather modeling has come a long way in the intervening 6 years, so they were able to come to new conclusions.

“We used a coupled magnetohydrodynamic(MHD)-ring current-ionosphere computer model,” says Welling. “MHD results contain far more complexity and, hopefully, better reflect the real-world system.”

Above: Sample results from computer modeling a Perfect CME impact. The images show the distortion and compression of Earth’s magnetic field as well as induced currents in the atmosphere. Source: Welling et al, 2020.

The team found that geomagnetic disturbances in response to a Perfect CME could be 10 times stronger than Tsurutani and Lakhina calculated, particularly at latitudes above 45 to 50 degrees. “[Our results] exceed values observed during many past extreme events, including the March 1989 storm that brought down the Hydro-Quebec power grid in eastern Canada; the May 1921 railroad storm; and the Carrington Event itself,” says Welling.

A key result of the new study is how the CME would distort and compress Earth’s magnetosphere. The strike would push the magnetopause down until it is only 2 Earth-radii above our planet’s surface. Satellites in Earth orbit would suddenly find themselves exposed to a hail of energetic charged particles, potentially short-circuiting sensitive electronics. A “superfountain” of oxygen ions rising up from the top of Earth’s atmosphere might literally drag satellites down, hastening their demise. (Note: Welling’s group stopped short of modelling the superfountain.)

For specialists, Table 1 from Welling et al’s paper compares their simulation of a Perfect CME impact (highlighted in yellow) to past extreme events:

You don’t have to understand all the numbers to get the gist of it. A Perfect CME strike would dwarf many previous storms.

Now for the good news: Perfect CMEs are rare.

Angelos Vourlidas of Johns Hopkins University has studied the statistics of CMEs. He notes that SOHO has captured only two CMEs with velocities greater than 3,000 km/s since the start of operations in 1996. “This means we expect roughly one CME ejected at speeds above 3000 km/s per solar cycle,” he says.  Speed isn’t the only factor, however. To be “perfect,” a 3000 km/s CME would need to follow another CME, clearing its path, and both CMEs must be aimed directly at Earth.

It all adds up to something that doesn’t happen every day. But one day, it will happen. As Welling et al conclude in their paper, “Further exploring and preparing for such extreme activity is important to mitigate space-weather related catastrophes.”

Read the original research here.

A Musical Note from the Magnetosphere

Jan. 19, 2021: High above the Arctic Circle in Lofoten, Norway, citizen scientist Rob Stammes operates a space weather monitoring station. His sensors detect ground currents, auroras, radio bursts, and disturbances in Earth’s magnetic field. Yesterday, he says, “I received a musical note from the magnetosphere.”

“Around 05.30 UTC on Jan. 18th, our local magnetic field began to swing back and forth in a rhythmic pattern,” he says. “Electrical currents in the ground did the same thing. It was a nearly pure sine wave–like a low frequency musical note. The episode lastesd for more than 2 hours.”

Stammes has received such notes before, but they are rare. “I see a pattern like this only about once a year,” he says.

Space physicists call this phenomenon a “pulsation continuous” or “Pc” for short. Imagine blowing across a piece of paper, making it flutter with your breath. Solar wind does the same thing to magnetic fields. Pc waves are essentially flutters propagating down the flanks of Earth’s magnetosphere excited by the breath of the sun.

Above: A magnetometer in Abisko, Sweden, recorded the same waves

Yesterday’s set of waves washed over Norway and Sweden, but almost nowhere else, according to the global INTERMAGNET network of magnetometers. It was a strictly regional phenomenon.

What happens in the sky when such a pure tone emerges from the natural background cacophony of magnetic activity? “I wish I knew,” says Stammes. “I was asleep at the time.” In fact, it’s possible that no one knows. Tones like these are rare, and they all too often occur while skies are cloudy or daylit, blocking any peculiar auroras from view. Stammes says he plans to build an alert system to help him find out. No pun intended: Stay tuned.

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!