Solar jet stream promises better flare forecasting
The earth's jet stream has a major influence on weather. Now, it seems like the sun has one, too. Richard A. Lovett reports.
Scientists studying 360-degree images of the sun have discovered that deep in its atmosphere, its magnetic field makes looping meanders intriguingly analogous to the earth’s jet stream.
Technically known as Rossby waves, these meanders were traced by observing their effect on coronal brightpoints — small bright features that dot the sun.
Their movements can be used to track motions deeper in the solar atmosphere. They are not particularly fast, especially when measured against the huge scale of the sun itself.
“We get speeds of three metres per second,” says Scott McIntosh, a solar physicist from the National Centre for Atmospheric Research in Boulder, Colorado, USA. “Slow, but measurable.”
Tracking the movements is difficult from earth, however, because we can only see one side of the sun at a time. That’s a problem because it rotates approximately once every 24 days, meaning that each portion of its surface is out of sight for 12.
However, for three years, from 2011 to 2014, solar scientists had a unique opportunity, because there were three deep-space satellites observing the sun all at once, spaced so their divergent angles allowed the entire surface to be seen simultaneously. Two were a pair known as the Solar TErrestrial RElations Observatory (STEREO), specifically designed for the purpose. The third was NASA’s Deep Solar Dynamics Observatory (SDO), which sits directly between the earth and the sun.
Collectively, the trio was able to monitor the whole shebang until 2014, when something went wrong with one of the STEREO spacecraft and it lost contact with its controllers. But three years of data were more than enough for McIntosh’s team to track the slow movements of the brightpoints and realise what that revealed about the existence of Rossby waves in the underlying magnetic field.
Rossby waves are important, because on earth changes in the jet stream are major factors in influencing local weather patterns. And now that we know similar features exist in the sun’s magnetic field, McIntosh says, we may be able to learn how they relate to the formation of sunspots, active regions, and solar flares. If so, it opens the door to forecasting solar storms long before they might hit us.
“This is exciting work,” says Daniel Baker, director of the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder, who was not part of the study team. “Those of us interested in the ‘space weather’ effects of solar activity can really applaud.”
Predicting space weather is important, because solar storms can hurl dangerous radiation at astronauts, damage satellites, interfere with communications and navigation systems, potentially take out electrical generators and wreak havoc on electronics.
“Estimates put the cost of space weather hazards at $10 billion per year,” says Ilia Roussev, program director in the US National Science Foundation (NSF) Division of Atmospheric and Geospace Sciences.
Historically there have occasionally been truly giant solar storms that if replicated today would have a devastating effect on modern technological society.
“I always tell people we live in the atmosphere of our star,” McIntosh says, referring to the solar wind. “What we have [in terms of technology], it could easily take away any time, in the blink of an eye. But because 99.99% of the time it rises in the morning and sets in the evening without doing any damage, we take it for granted.”
What’s now needed, he adds, is to restore our ability to view the whole 360-degree surface of the sun, all at once, perhaps by such methods as placing a constellation of spacecraft in orbit around it. “These are things I’d like to see in my lifetime,” he says.
The study was published 27 March in Nature Astronomy.