File:Evolving Sigmoid Loops -Hinode XRT-.webm
This sequence of images (click for the movie) depicts active region 11093 on 11-Aug-2010. As you can see, the collection of loops, when viewed all together, resemble a large backwards 'S'. For this reason we call such an active region "sigmoidal". Most of the time, there's no one single loop that traces out a full S-shape, but in this case XRT happened to catch a pair of shorter loops joining together to complete the shape. At 01:50:20, there is a clear gap between the northern and southern loops; but just a few minutes later (01:56:37) a bright knot begins to appear. By 02:09:15, the bright knot is too intense for XRT's detector, resulting in the big bloom of saturated pixels. This indicates that a large amount of energy was released at the junction of those two loops, causing the plasma to be super-heated to millions of degrees. And at 02:16:35 we can see the result: the connection of "north loop" to "south loop" has created a single long, S-shaped loop. It's the act of connecting those loops -- a process referred to as "magnetic reconnection" -- that releases the energy and produces the heat.
Questions and comments welcome at xrtpow "at" gmail "dot" com
Hinode is a Japanese mission developed and launched by ISAS/JAXA, with NAOJ as domestic partner and NASA and STFC (UK) as international partners. It is operated by these agencies in co-operation with ESA and the NSC (Norway).
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