Quiet week, lovely events

Solar flaring activity was once again restricted to a handful of minor C-class flares this week. A few regions drew away all attention: Departing NOAA 2546, emerging NOAA 2548, and an active but spotless region near the Sun's east limb.



NOAA 2546 consisted mainly of a single big sunspot, with a surface area about three times that of the Earth. During its two weeks of visibility on the solar disk, it produced only three C-class flares. However, its symmetrical and simple outlook in white light was rather misleading, as extreme ultraviolet (EUV) imagery from SDO showed a large number of jetlike eruptions from 24 to 26 May, often -but not always- associated with minor eruptions in x-ray flux and small coronal mass ejections (CMEs). The region rotated over the southwestern solar limb late on 26 May.

NOAA 2548 gradually emerged on disk starting 24 May, showing some interesting magnetic restructuring during its initial development. The presence of a few patches of opposite magnetic polarity near the main spot resulted in the creation of a couple of small filaments. All this activity sparked some minor B-class flaring and also one C-class flare, on 26 May peaking just 15 minutes before the C-class event in NOAA 2546. Interestingly, the main leading spot of NOAA 2548 was directed away from the solar equator, in contrast to the general rule that the leading portion of a sunspot group is located closer to the equator than the trailing portion.

An active region does not need to have spots to produce flares or other eruptive events. Indeed, early on 29 May, a small, spotless region near the northeastern limb produced a gradual, long duration B3 event. It was associated with a very nice CME, as captured by the PROBA2/SWAP and SDO/AIA EUV-telescopes. The typical post-flare coronal loops were observed, and coronagraphs revealed a nicely shaped CME. None of the aforementioned CMEs had an earth-directed component.