Active Region NOAA 1777
posted: June 25, 2013

During the early hours of 21 June, the relatively simple sunspot group NOAA 1777 unleashed a medium class solar flare. The M2.9 flare peaked at 03:14UT, and lasted for 73 minutes. Its x-ray signature clearly dominated the x-ray solar activity for that day.

This movie gives mainly some SDO/AIA views on the solar flare, the post-flare coronal loops and the ejected material. The ejected material could be observed all the way into the field-of-view of the PROBA2's SWAP-instrument, indicating hot material was involved.

The last clip of the movie contains STEREO-B views on this region on 18 and 19 June, when NOAA 1777 was still behind the east limb as seen from Earth. Clearly, the ejected material can be traced back to the active region displaying a nearly circular bright feature (in the 19.5 nm filter). See the STEREO-B combo image underneath, taken around noon on 19 June.

As NOAA 1777 rounded the east limb, earth-based observatories and earth-orbiting satellites got a better view on this region. The circular feature was still present (SDO/AIA 193, image to the left), and was associated with somewhat stronger magnetic fields. These fields had a magnetic polarity opposite to those closer to the main spot (SDO/AIA magnetogram to the right). H-alpha imagery from the GONG-observatories showed filaments trapped between these opposite magnetic areas (image in the middle).

Interestingly, NOAA 1777 has a magnetically polarity which is opposite to that of the main spots of sunspot regions that appear on the southern hemisphere of the ongoing solar cycle. Indeed, the main spot has a reddish color indicating negative polarity (fields returning to the solar surface), whereas the main spots in other southern groups have normally a positive polarity. From statistics of previous solar cycles, about 3% of all sunspot groups show this "aberration". So, it's not such an unusual feature, but it may be an intriguing element in the overall activity of this active sunspot group.

Credits - Images were taken from SDO/AIA, SOHO/Lasco, STEREO-B, PROBA2/SWAP, and the GONG/H-alpha network..