A sunspot accident!
posted: February 17, 2016

A movie of this event can be found here.

Once more, two sunspot groups have collided with each other. Indeed, NOAA 2497 was minding its own business when, starting on 11 February, the trailing part of a smaller sunspot group suddenly emerged right in front (to the west; "right") of it. It was unavoidable that the leading part of NOAA 2497 would bump into the trailing part of this new magnetic bipolar region, and it was easy for the space weather forecasters to predict that these developments could result in the production of low-level M-class ("medium") solar flares. In fact, whereas the region was relatively quiet until about 10 February, it produced one M-class flare every day starting 12 February.


The picture above shows the area in white light (left column) and the corresponding magnetogram (right column), as seen with the SDO/HMI instrument. The dates are 10 February (around 00:00UT; top), 12 February (around 00:00UT; middle), and 14 February (around 00:00UT; bottom). In the magnetogram, the yellow and red colors represent positive magnetic polarity (magnetic field lines coming out of the solar surface), whereas the green and blue colors are used for negative polarity (magnetic field returning into the solar surface). As the positive, trailing part of the new region drapes itself around NOAA 2497's main leading spot, a very complex sunspot structure is created with several delta's (spots of opposite magnetic polarity within the same penumbra; see e.g. this news item). This intensified the solar flare activity, with an increasing number of C-class flares and an M1 flare on 12 (10:47UT), 13 (15:24UT) and 14 (19:26UT) February. These flares took mostly place near the locations of opposite polarity. This can be seen in the picture underneath of the first M1 flare, with the magnetogram (11:52UT; top), an SDO image in extreme ultraviolet (EUV) overlaid on the magnetogram (10:52UT; middle), and another SDO EUV/magnetogram combo but at a temperature of several million degrees (10:49UT, bottom).


This movie shows the evolution in white light, the magnetogram, and the combined white-light and magnetogram clip from 10 till 14 February. The EUV-magnetogram clips cover the period from 12 till 14 February. It seems that lawmakers and insurance companies could really have a good time with all those reckless sunspot groups (see e.g. also this news item for more examples).