Spirals of solar wind can spin off larger solar eruptions and disrupt Earth's magnetic field, yet they are too difficult to detect with our current single-location warning system, according to a new study from the University of Michigan.
But a constellation of spacecraft, including one that sails on sunlight, could help find the tornado-like features in time to protect equipment on Earth and in orbit.
The study results come from computer simulations of a massive cloud of plasma erupting from the sun and moving through the solar system. Because the simulation covers features that span distances three times Earth's diameter down to thousands of miles, the researchers could determine how smaller, tornado-like spirals of plasma and magnetic field—called flux ropes—become concerning features in their own right.
"Our simulation shows that the magnetic field in these vortices can be strong enough to trigger a geomagnetic storm and cause some real trouble," said Chip Manchester, research professor of climate and space sciences and engineering and the corresponding author of the study published in the Astrophysical Journal.
In May 2024, a geomagnetic storm tripped high-voltage power lines, disrupted satellite orbits,and forced some airplanes to change course. It also scrambled navigation systems on tractors in the Midwest, which NASA says cost each affected farm $17,000 in damages, on average. For both scientific curiosity and better warning systems ahead of these events, NASA and the National Science Foundation funded this U-M study.
Geomagnetic storms are triggered by magnetic fields in the solar wind, a bubble of plasma that flows outward from the sun and envelops the solar system. Like wind on Earth, the solar wind blows in varying patterns that comprise space weather. Eruptions at the sun create the most extreme space weather—dense, fast-moving clouds of plasma called coronal mass ejections that span 34 million miles, on average.
But scientists have also noticed relatively small flux ropes in the solar wind, between 3,000 and 6 million miles wide. These features are too small for typical simulations of coronal mass ejections, which could only produce features larger than 7 million miles wide, but they are also too large for simulations often used to study magnetic fields and plasma particles in the solar wind. The new simulation allows researchers to see these features of intermediate size along with large coronal mass ejections.
The U-M simulation suggested that the tornado-like flux ropes form out of the coronal mass ejections as they drive through slower solar wind, flinging aside spinning masses of plasma like a snowplow tossing snow. Some tornadoes dissipate, but more persistent vortices can form during collisions with neighboring streams of fast and slow solar wind. Telescopes pointing at the sun look for eruptions to warn of bad space weather, but for flux ropes, the researchers say that's not enough.
"If there are hazards forming out in space between the sun and Earth, we can't just look at the sun," said study co-author Mojtaba Akhavan-Tafti, associate research scientist of climate and space sciences and engineering. "This is a matter of national security. We need to proactively find structures like these Earth-bound flux ropes and predict what they will look like at Earth to make reliable space weather warnings for electric grid planners, airline dispatchers and farmers."
The solar wind can only trigger geomagnetic storms when its magnetic field has a strong southward orientation. Spacecraft stationed between Earth and the sun already help scientists make space weather warnings by measuring the speed of the solar wind, as well as the strength and direction of its magnetic field. But a solar eruption aimed away from Earth, or with northward-pointing magnetic fields, might still toss vortices with southward-pointing magnetic fields toward Earth. Those tornadoes would go unnoticed if they miss the probes stationed at L1.
"Imagine if you could only monitor a hurricane remotely with the measurements from one wind gauge," Manchester said. "You'd see a change in the measurements, but you wouldn't see the storm's entire structure. That's the current situation with single-spacecraft systems. We need viewpoints from multiple space weather stations."
The researchers hope to provide that multiprobe view of solar tornadoes with a constellation of spacecraft called the Space Weather Investigation Frontier, or SWIFT, which was developed in a NASA mission concept study led by Akhavan-Tafti.
In the current proposal, four probes would be stationed in a triangular-pyramid formation, around 200,000 miles apart. Three identical probes would occupy each corner of the pyramid's base, located in a plane around L1. A final "hub spacecraft," located beyond L1, would serve as the pyramid's apex, pointing toward the sun. This configuration would allow SWIFT to see how the solar wind changes on its way to Earth, and its hub closer to the sun could make space weather warnings 40% faster.
The apex's location would normally require an impractical amount of fuel to fight the sun's gravity, but NASA engineers, through their Solar Cruiser mission, designed an aluminum sail that could enable the probe to park beyond L1. The sail would cover about a third of a football field, allowing it to catch enough photons to maintain the spacecraft's position without burning fuel.
Study: High-resolution simulation of CME-CIR interactions: small- to mesoscale solar wind structure formation observable by the SWIFT constellation (DOI: 10.3847/1538-4357/adf855, available upon request or when the embargo lifts)
Journal
The Astrophysical Journal