Solar activity has been very low over the last few weeks, with the last big solar flare already dating back to 25 June. That day, NOAA 2371 produced the last and strongest of its series of 6 M-class flares. The M7.9 flare peaked at 08:16UT and its space weather effects were extensively discussed in the 3 July 2015 Newsletter.
The most amazing aspect of this eruption were the complex series of post-flare coronal loops that accompanied this event. The above pictures were taken on 11:21UT. An extreme ultra-violet (EUV) SDO/AIA 171 image has been laid over resp. an SDO/HMI white light image (top) and a magnetogram (bottom; red is positive polarity, blue is negative). It shows that the flare took place mostly in the trailing portion of the sunspot group, with the footpoints of the coronal loops anchored in the opposite polarity patches of which this area was made up. The coronal loops are huge. The picture below shows a zoom on the EUV image overlaid on the white light image, with the Earth sized to the same scale. The main spots are large enough to accomodate one Earth at least, but it would require several Earths to fit the entire height of the coronal loops!
The images below are stills from the movie , covering the time span from 07:30UT till 14:30UT. These are combination images from SDO/AIA 171, 193 and 131, showing essentially the hot parts of the eruption. The yellow-orange colors denote temperatures of about 700.000 degrees, the blue hues show very hot areas with temperatures of several million degrees. The top image was taken at 08:40UT and shows the flare in progress as well as some coronal dimming to the southwest. The bottom image was taken at 11:21UT and shows the complexity of the arcade. The coronal loops continued to grow and remained visible for the rest of the day as the magnetic fields kept on restructuring.
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