Energy ribbons cause solar flare

BY KULVINDER SINGH CHADHA

ASTRONOMY NOW

Posted: 20 April, 2009

Tight ribbons of energy on the Sun called sigmoids have been found to cause explosive solar flare events. X-ray telescopes can see these sigmoids in the Sun's corona (it's tenuous outer atmosphere), but models produced by scientists from St Andrews University and the Harvard Smithsonian Center for Astrophysics explain how they form. The results will be presented at the Joint European National Astronomy Meeting at Hertfordshire University (UK) by Professor Alan Hood and Dr Vasilis Archontis, both from St Andrews.

Figure showing the time evolution and eruption of a sigmoid. The first column shows surfaces of electrical current and the second one shows temperature (white hottest, black coolest). These are both simulations form the model. The third column shows Hinode's observations of a sigmoid. Image: ISAS/JAXA/NAOJ/NASA/STFC/ESA/NSC.

Observations by the Hinode spacecraft's X-ray telescope (XRT) showed the formation and eruption of a sigmoid at high resolution. It revealed that sigmoids have a complex structure: two, J-shaped bundles meeting together to form an 'S' shape. An explosive flare event signals the end of a sigmoid's life. However, no one has been able to explain their complex structure and behaviour until now.

The St Andrews team's model treats sigmoids as consisting of numerous thin, twisted ribbons of electrical current. A flare event occurs when these layers interact, throwing magnetic fields and charged particles into space. Archontis says, "Sigmoids work as 'mangers' or 'cocoons' for solar eruptions and there is a high probability they will result in powerful eruptions and other explosive events." He adds that the new model will help scientists understand how this happens.

Hood explains the importance of predicting solar flare events. "Sigmoids are amongst the most interesting features for scientists trying to forecast solar eruptions as these events can disrupt telecommunications, damage satellites and affect the way navigation systems operate."

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