How are solar flares formed?
(by Amara Graps)
The short answer is that we don't know exactly. And we cannot reliably predict them. Solar physicists are working on figuring out how solar flares form. It is an active area of research.
Solar flares are brief, enormous outbursts of power. In a few minutes, the disturbance on the surface of the Sun spreads along the Sun's magnetic field lines, releasing energy equivalent to billions of nuclear explosions (producing X rays) and raising the temperature of the flare region (which is about the size of the Earth) to tens of millions of degrees and lasting minutes to hours. (1) Sometimes the flare goes temporarily out of control and loses equilibrium, becoming hotter than the core of the Sun itself for a short period of time.
Solar flares seem to be related to sudden release of stored magnetic energy, and they are more active during the "solar maximum" part of the 11 year cycle of solar activity, but the exact cause is still unclear because we don't know enough about how magnetic fields work on the Sun. Solar flares also are generally believed to originate in the low coronal atmosphere (2), which is the part of the Sun above the photosphere. Here is a simple diagram of the layers of the Sun.
One simplified picture that the scientists have for the cause of a solar flare is the following:
Imagine the magnetic field on the Sun as loops like rubber bands that wrap around the Sun, with one end attached to the south pole and the other end attached to the north pole. The Sun is rotating, so as the Sun rotates, the magnetic loops wrap tigher and tighter until it is wound up so tight that the fields ("rubber bands") snap! Where the magnetic field snaps is where active regions on the Sun form and where the flare erupts on the solar surface.
But this is just one plausible scenario, and the scientists are not sure about the details of that picture.
(1) Kenneth Lang, _Sun, Earth, and Sky_, Springer Verlag, 1995, pg. 131.
(2) ibid. pg. 135
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Special Thanks to A. Graps.