When the sun blasts a packet of energetic particles our way, beautiful auroras come out to play: ribbons of vibrant lights dancing about in the sky close to the north and south magnetic poles. But every now and then, a mysterious fuzzy patch of auroral lights hovers over the North Pole. It hasn’t been clear what these lights are or what’s producing them, particularly as they have appeared during quiet periods for the sun.
An international team of scientists may have finally figured it out. These spots could be the northern lights rotating in an unorthodox spiral shape similar to the familiar shape of a hurricane—a phenomenon the team has dubbed a “space hurricane.”
While combing reams of data collected by a Cold War-era satellite program, researchers spied a burst of auroral emissions over the North Pole captured in unprecedented detail. As reported in a study published in February’s Nature Communications, an unusual aurora that appeared in 2014 over the North Pole had a calm center, or “eye,” with strong “winds” of plasma—electrically excited gas—zipping around it in a vortex-like manner. Lasting for around eight hours, it was more than 620 miles across and stretched from its base 60 miles above sea level to 500 miles high, reaching into space.
Such auroral patches seen prior to 2014 also may have been space hurricanes. If so, that means the 2014 event isn’t a new discovery per se. But, says study co-author Kjellmar Oksavik, a space physics researcher at the University of Bergen in Norway, “this is the first time that we’ve seen that it’s actually a hurricane, in shape and form and behavior.”
Uncertainties remain, including how commonplace space hurricanes are and how much energy transfer into Earth’s atmosphere is involved.
Hunting down space hurricanes
Over the past few years, Qing-He Zhang at Shandong University in China and the study’s lead author has been looking through satellite data with his students in an attempt to find interesting upper-atmospheric phenomena. One such dataset came courtesy of the Defense Meteorological Satellite Program, originally set up by the U.S. in the 1960s to track the world’s weather and help the U.S. armed forces plan military operations.
Zhang explains that since hurricane-like entities exist in the clouds of Jupiter, Saturn, Uranus, and Neptune—for example, Jupiter’s Great Red Spot—as well as on Earth, he was curious as to whether something similar could exist in the uppermost atmospheres of planets. Earth, surrounded by satellites, seemed a good place to start looking.
Satellites have previously spied suspicious auroral patches over the north magnetic pole, but those eyes in the sky never had the right orbits or cameras to see more than just a blur. U.S. military satellites, however, orbit far closer to Earth and carry instruments that can clearly spot such auroras. Although this setup is perfect to find a space hurricane, it still wasn’t an easy task for the researchers—not knowing when it may be most likely to appear and what may be the key features of a space hurricane. “You don’t know what you’re looking for,” Oksavik says.
Those satellites spied a cyclone-like auroral spot spinning right atop the north magnetic pole on August 20, 2014, one that resembled a hurricane. But the solar activity at the time was all wrong for it. The alignment of the sun’s extended magnetic field wasn’t conducive to a strong aurora and the solar wind—the stream of particles and magnetism fired off into space by the sun—was moving slowly and lacked many energetic particles.
How could this aurora exist?
You spin me right round
First, it’s important to understand how regular auroras appear.
Electrons jettisoned from the sun spiral down to the magnetic poles. They slam into neutral gas atoms and molecules in the upper atmosphere, temporarily energizing them and causing flashes of light. That light—whites, reds, violets, blues, greens, and reds, depending on the specific gases being pinged—makes up the northern and southern lights.
The northern lights appear in something called the auroral oval, essentially a ring around magnetic north that expands and contracts as the Earth’s magnetic field responds to the supersonic solar wind and the sun’s magnetic field.
A wide auroral oval happens when the sun’s magnetic field points south while it interacts with the dayside section of Earth’s magnetic field, which points north as it flows around the planet. During a solar storm, in which electrons and parts of the sun’s magnetic field fly toward Earth, the sun and Earth’s magnetic fields can couple together, a bit like two opposing ends of a bar magnet. This coupling sets up a strong magnetic pathway between the sun and Earth, allowing electrons and positive ions from the solar wind to rush down into the Earth’s atmosphere at the poles.
To explain the weird hurricane-like 2014 auroral vortex—a spinning lightshow tightly packed around the magnetic north—the team attempted to replicate what the satellites saw in a 3D model that can simulate the movements of magnetic fluids.
At that time, the sun’s magnetic compass was pointing very strongly north, so the coupling with Earth’s magnetic field was extremely weak. That caused the auroral oval to contract into a small spot atop the magnetic north pole.
Even during the mild solar wind conditions present that day, electrons still rained down into Earth’s upper atmosphere. Over a wide auroral oval they would normally produce dim auroras. But as they were falling into such a tight oval that day, more gas atoms and molecules were being pinged in that specific spot than usual, creating a brighter auroral glow than one would expect.
Finally, the solar wind also had an east-west magnetic component. This isn’t especially unusual, but when applied to such a highly constricted auroral oval, it effectively pushed it, causing the aurora to spin. And voilà, a space hurricane.
A tale of two hurricanes
As the study authors acknowledge, comparisons to the hurricanes born atop Earth’s oceans aren’t perfect.
Both have calm eyes, and matter spins around the eye at breakneck speeds in spiral arms. “The analogy is certainly evocative,” says Daniel Swain, a climate scientist at the University of California, Los Angeles who wasn’t involved with the research. But, he notes, the two are fundamentally different things. A hurricane is essentially a heat engine that extracts energy from the oceans in the tropics and transfers it to the poles. The physical processes involved with a space hurricane are entirely different.
The word hurricane may also invoke the image of something massive, furious, and destructive, as earthly hurricanes can be. Could space hurricanes also prove to be a threat?
Radio and satellite communications bouncing off the atmosphere above magnetic north could, for example, offset GPS-derived map positions for Arctic explorers. The electrons falling into a tight oval may also heat up the atmosphere below enough to cause it to expand and bulge upwards. This could slow down satellites as they pass through this dense atmospheric pocket.
But the effects are likely to be very minor. Geomagnetic storms created by far more powerful solar outbursts, the sort capable of frying electrical infrastructure the world over, are the real space weather danger, says Alexa Halford, a space physics researcher at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who wasn’t involved in the study.
Pirouetting in the darkness
The hunt is on for more space hurricanes. Now that the researchers know what features to look for, says Oksavik, algorithms can be written that can quickly spool through satellite data and identify other candidates. When they are found, they will help researchers better understand their behavior and should reveal whether they happen exclusively above the North Pole or whether they crop up down south too.
That the 2014 space hurricane appeared during a quiet solar cycle suggests that they are commonplace, because they don't require above-average solar activity to exist. And not just on Earth, but perhaps on other worlds with magnetic fields too, including the gas and ice giants and possibly even Jupiter’s moon Ganymede, the only moon with its own magnetic field.
But finding just one is exciting enough for now. “As humans, we think we know a lot about the universe and our own planet and what is around us,” Oksavik says. “And then we discover something we didn’t expect.”