Shoot-out at NOAA 1974
posted: February 21, 2014

What seemed to be a boring and declining sunspot group suddenly turned out to be the most flare productive group of the week.

On 9 February, NOAA 1974 was a relatively small group with almost no spots in its trailing end. Then, in the course of the day, new magnetic flux emerged in this trailing portion gradually increasing its sunspot area to nearly 6 times the surface area of the Earth by 15 February. In view of the close proximity of the sunspot groups (less than 10 degrees in heliographic longitude), this region was still considered as 1 sunspot group.

Some of the magnetic strands of the newly emerging flux were of a polarity opposite to that of the trailing section. As this flux migrated to the west (towards the leading portion), it logically resulted in increased flaring activity. However, as the associated, closely-packed sunspots were rather small, only medium flares resulted from their interaction. In only 4 days (11-14 February), this active region barreled 14 M-class flares in quick succession, the strongest being an M3.7 flare on 12 February.

Both in the SDO images above and below, as well as in the movie, the red color means negative magnetic fields (returning to the solar surface), whereas blue indicates positive magnetic field (emerging from the solar surface).

After 14 February, the magnetic delta's (see previous newsletter) had been neutralized, and newly emerging flux in the northern portion of the region only added to the sunspot area, without the production of new delta's or additional medium class solar flares. As the region is transiting the Sun's backside now, the STEREO spacecraft have the best view on how this group further develops. Within 2 weeks, we'll see if new magnetic flux has emerged and the group is still flare active, or if it has decreased in size or maybe completely vanished from the solar surface.