El Magnifico
posted: May 29, 2013

A very impressive solar eruption took place on 22 May. Source region was the -at that time- not very impressive sunspot group NOAA 1745, near the northwest limb. The SDO-pictures underneath show the region at 15:00UT in white light and in EUV. From this relatively tiny sunspot, one would not expect so much ongoing flare activity.

The M5 flare peaked at 13:32UT and lasted for an hour (long duration event). This movie starts by showing the flare in successively higher temperatures of the solar atmosphere: First H-alpha (chromosphere, +/- 10.000 degrees), then AIA 171 (transition region, 650.000 degrees) and AIA 094 (corona, several million degrees). The next two clips are combo's of various AIA-filters, showing the evolution of this magnificent flare in EUV.

From these, one can see that the flare was probably the result of some destabilization following the interaction between NOAA 1748 and the trailing part of NOAA 1745. This activity preceded the main event by several hours, and resulted in some reconnection (AIA 094) and a small coronal mass ejection (CME) as can be seen in the SOHO and STEREO movies around 9:00-10:00UT.

The flare was certainly an important event. In H-alpha, it measured "3" on a maximum scale of 4, meaning that the flare extended over a very wide area, comparable to 5 or 6 times the entire surface of the Earth. Only 0.4% of the flares in H-alpha reach such an extent. Also, the post-flare coronal loops were very dynamic and large, and lasted well into the next day.

More importantly, the flare was also accompanied by a strong proton event, lasting for nearly 3 days. It was also the strongest so far this year, and the third strongest of the ongoing solar cycle, after the January and March 2012 events. Protons slamming unto the detectors of the solar telescopes saturate the camera's pixels which results in a lot of noise (white dots and stripes) and a reduction in the quality of the image.

In extreme cases, the degraded images prohibit the finder telescope to actually find the proper reference stars, which occasionally results in the satellite pointing its solar panels away from the Sun, thus cutting itself off from the much needed electricity. For example, last week’s proton storm pretty much obscured the view on the Pleiades (see this news item ; SOHO/Lasco image underneath).

The CME associated with this M5 flare was quite solid and big too. Seen by SOHO/Lasco, it was a halo CME moving at a speed of at least 1.000 km/s. Though mostly moving away from the Earth, part of the CME impacted the Earth late on 24 May, meaning a travel time of about 53 hours. Geomagnetic storming conditions were observed. STEREO-A's coronagraphs also saw a halo CME, but due to its position near the east limb (as seen by STEREO-A), it took the plasma cloud about 12 hours longer to reach the satellite (see STEREO-A's in situ measurements).

Credits - Data and imagery for the movie clips were taken from the GONG H-alpha network, SDO, STEREO, PROBA2/SWAP, and SOHO/LASCO.