By Jack Lee, San Francisco Chronicle The Tribune Content Agency
Vivid streaks of red, magenta and green illuminated night skies in recent months, when the northern lights made it all the way down to California. Aurora chasers will be excited to hear that additional viewing chances could come in the near future due to heightened solar activity.
In October, NASA and the National Oceanic and Atmospheric Administration announced the sun has reached the maximum phase of the solar cycle and that this peak could continue for the next year.
"There is a lot of potential to see more space weather events," said astrophysicist Sushant Mahajan, a research scientist at the W.W. Hansen Experimental Physics Lab at Stanford University.
Solar activity rises and falls on a natural cycle that lasts roughly 11 years. During solar maximum, "the sun transitions from being rather sluggish to being really active and stormy," said Kelly Korreck, program scientist in NASA's Heliophysics Division during a media briefing.
The sun's magnetic field also completely flips at the cycle's peak: "That'd be like the North Pole and the South Pole (on Earth) swapping places basically every decade," Korreck said.
The rise in solar activity is accompanied by an increase in the number of sunspots, dark regions on the sun's surface caused by concentrations of magnetic field.
Sunspots are associated with solar activity. A large, complex sunspot cluster that was 17 times the size of Earth was the source for a historic geomagnetic storm in May.
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"A barrage of large solar flares and coronal mass ejections, or CMEs, launched clouds of charged particles and magnetic fields toward Earth, creating the strongest solar storm to reach Earth in two decades - and possibly one of the strongest displays of auroras on record in the past 500 years," said Elsayed Talaat, director of NOAA's Office of Space Weather Observations, during the briefing.
The current solar cycle, dubbed solar cycle 25, has been more active than its predecessor. But previous centuries have produced stronger cycles with higher numbers of sunspots. The chart shows how average sunspot numbers fluctuated over 275 years, based on data from the Royal Observatory of Belgium.
Based on the peak number of sunspots, the previous cycle had the lowest amplitude in a century, Mahajan said. That cycle lasted from December 2008 to December 2019.
The current solar cycle is also relatively weak, with a provisional average of 144.4 sunspots for April 2024. By comparison, solar cycle 19 peaked at 285 sunspots in March 1958.
Much bigger storms have also occurred in the past. The Carrington Event in 1859 and storms in 1872 and 1921 were all several times bigger than the May storm, said Bill Murtagh, program coordinator with NOAA's Space Weather Prediction Center, during the briefing. The 1859 event caused telegraph systems around the world to fail, with sparking equipment even causing fires. Such a storm today could wreak havoc on telecommunications, GPS and the power grid.
And the current solar cycle is still expected to bring impactful events.
"We are anticipating another year or so of maximum phase, before we really enter the declining phase, which will lead us back to solar minimum," said Lisa Upton, co-chair of the Solar Cycle 25 Prediction Panel and lead scientist at the Southwest Research Institute, during the briefing.
The decrease from solar maximum to minimum typically takes several years and the declining phase can still include very strong solar events.
Extreme solar storms in late October 2023, for example, occurred 3 1/2 years after a solar maximum. The storms produced stunning auroral displays, but also caused problems with satellites and radio communication.
Additional solar and geomagnetic storms in the coming months could have similar impacts, for better and for worse.
"Everyone across the nation loves the aurora borealis ... the bigger the storm, the more visible the aurora, the further south it's visible," said Murtagh, of the Space Weather Prediction Center. "But at the same time we can't be hoping for these big displays, because with them comes the threat to our critical infrastructure, so we always have to be careful with what we wish for."
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