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Pop! Goes the Solar Flare
FOR 30 YEARS Terry Forbes has been pondering the inner workings of a phenomenon that occurs throughout the universe, greatly affects life here on Earth, and is analogous to the physical process that springs a Jack-in-the-Box.

“It sounds whimsical I know,” Forbes says of the analogy between a solar flare and the old-fashioned children’s toy, “but you have a coiled spring that gets compressed with a crank and then at a certain point the spring releases and, Pop! Goes the Weasel.”


Terry Forbes
Terry Forbes
Photo by K. Donahue, UNH-EOS
And so it goes when the Sun hurls out a coronal mass ejection – “just a fancy name for a solar flare,” asserts Forbes, a solar theorist and research professor in the Space Science Center and Department of Physics, and who was recently honored by UNH with a Faculty Award in Excellence in Research.

“What I think happens with a solar flare is, and a lot of people are on the same track, instead of a coiled spring you have a coiled, twisted magnetic field that can store energy in the same way the spring in the Jack-in-the-Box does,” he explains.

However, Forbes notes, the puzzling thing is why so many of the magnetic “springs” sit for so long before suddenly flying off in an explosion of plasma.

“You can see the uncoiling going on and do more quantitative calculations related to magnetic theory – so it’s pretty clear that the main source of energy for these flares is twisted magnetic fields. What we don’t quite understand yet is the mechanism that makes Jack leap out of the box.”

Because such flares are rather common on stars in general, and also occur in more exotic things like black holes and accretion disks, understanding the underlying physics of what makes them tick has broader implications than, say, just getting a better handle on how solar flares affect space weather near Earth.

The term “space weather” generally refers to conditions on the Sun, in the solar wind, and within Earth’s magnetosphere and upper atmosphere that can influence the performance and reliability of space-borne and ground-based technological systems and can pose risks to astronauts and people onboard aircraft in polar regions.

“For me, the motivation in doing this research is just curiosity, there doesn’t need to be any practical application,” Forbes says adding, “it’s just such a fascinating thing, and when something fascinating happens you want to know why.” (Forbes remembers well his own Jack-in-the-Box and, as a child, puzzling over the unseen mechanism that, to the exact turn of the crank, launched the captive puppet.)

Forbes notes, however, that luckily for him and colleagues with a similar scientific bent there are programs to support both the basic science (“the curiosity thing”) and the practical applications of solar flare research.

“Most of my funding right now comes from the National Science Foundation and NASA – some of it for basic science and some for the Space Weather Program, which a lot of other people at EOS are involved with, trying to predict these events,” he says.

Indeed, Forbes notes that while there are perhaps some 1,000 scientists worldwide doing work similar to his, you can’t swing a dead cat in Forbes’ EOS neighborhood without hitting a solar flare theorist. “Sitting here it looks like everybody and their brother does solar flares. You’re in a hot spot here at UNH.”

In a sense, solar flare scientists here at UNH and elsewhere are carrying on work first initiated by English amateur astronomer Richard Carrington in the mid-1800s.

Carrington, who had been faithfully recording sunspots using a telescope to project an image of the Sun on paper, witnessed a tremendous coronal mass ejection in September of 1859 – as did the rest of the world. On that day the entire Earth was engulfed in the Sun’s gaseous blast; there were aurora from pole to pole, telegraph systems crashed and electric shocks knocked operators unconscious. It was Carrington who connected the dots, put solar flares on the map, and helped usher in modern astronomy.

But it wasn’t until after World War II and the dawn of x-ray astronomy that scientists began to see solar flares more clearly.

Up until that time the natural tendency, based on observations, was to assume the flares originated from the Sun’s surface or chromosphere. However, x-ray telescopes revealed for the first time that the solar Jack-in-the-Box appeared to be popping up from the Sun’s atmosphere or corona.

Although naysayers remain, Forbes notes, “I think it’s pretty clear that it’s an atmospheric phenomenon.” But that’s hardly the end of the story.

Even with x-ray telescopes – like the Japanese Hinode X-Ray Telescope (XRT) mission on which Forbes is a co-investigator, the corona is a tricky area to investigate because of its magnetic nature.

“It’s almost impossible to see and that’s why there’s so much research on this because it’s kind of hard to make progress,” Forbes says. So he and other theorists spend their time “coming up with various schemes” of how the magnetic field might get twisted, evolve, and eventually fly apart.

It is for his decades-long efforts as a solar theorist that Forbes is recognized internationally as an expert in the field and was recently awarded by the university.

“Terry’s contributions to understanding magnetic fields in plasmas and explaining their behavior on the Sun have been truly outstanding,” says research professor Phil Isenberg who, like Forbes, is a member of the Solar-Terrestrial Theory Group within the Space Science Center. Adds Isenberg, “Here at UNH, Terry’s insights and willingness to work with research colleagues have benefited all of us and, for me, having Terry just down the hall to talk to and puzzle over problems with has been incredibly valuable, both scientifically and personally.”

Forbes’ efforts at making progress also include discussion with colleagues on the other side of the fence – the experimentalists.

“I always think its not really science unless the theory and experimental people talk to each other,” he says adding, “and it’s important for the theory people to keep their eye on the observations and not just wander off and come up with some real ivory-tower ideas that come crashing to the ground when compared to reality.” -DS


by David Sims, Science Writer, Institute for the Study of Earth, Oceans, and Space. Published in Summer 2009 issue of EOS Spheres.