NOAA 1515: pictures of the M6.9 flare on July 8

posted: July 10, 2012

As noted in a previous comment, NOAA 1515 produced 5 high energetic events during its transit. The last of these events was an M6.9-flare on July 8th that occurred while NOAA 1515 was already close to the western solar limb. The flare started at 16:23UT and reached its maximum x-ray intensity at 16:32UT. The images underneath show the eruption as seen by PROBA2/SWAP and in H-alpha during the flare's peak and at 16:54UT. One can clearly see that material is ejected from the blast site.

When the clouds of ejected particles are traveling through the Sun's hot atmosphere (the corona), radio wave disturbances are created that can be recorded with ground-based radio-telescopes. This is an observing branch to which both professional as non-professional observers contribute. The image underneath shows the radio spectrum from the Humain Radioastronomy Station as it was recorded between 16:15 and 16:45UT. In a radiospectrum, the intensity of a series of frequencies (Humain: between 45 and 445 MHz) is quickly and continuously scanned for these disturbances. Underneath the Humain recording is also a graph obtained by Felix Verbelen, leader of the Belgian Radioastronomy Section of the Vereniging Voor Sterrenkunde ( http://www.vvs.be/werkgroepen/ werkgroep-radioastronomie ). Monitoring at only one frequency (49.9 MHz: the green line on the Humain's radiospectrum), this radio-telescope is a lot more sensitive than the one from Humain. Nonetheless, both diagrams show the 3-stage-eruption very well: A type III radio-storm between 16:23 and 16:28UT, a type II storm between 16:30 and 16:36UT (at the peak of the solar flare), and a small disturbance around 16:42UT (barely visible in the Humain recording). It should be noted that the M6.9- flare occurred after the Humain station stopped tracking the Sun, and that at that time the antenna was put back at meridian (storage position).

Finally, the PROBA2-team combined images from 3 satellites (PROBA2, SDO and SOHO) into a movie showing the flare and the subsequent CME as it traveled through the Sun's corona: the movie Underneath are 3 stills from this clip. The first image shows the flare at 16:38UT, with material visibly leaving the solar surface. The second image was taken around 18:50UT, clearly showing how the solid CME from the flare is leaving the Sun. Interestingly, the third image taken around 22:10UT, shows that a second CME was hurled into space. The particle cloud originated from the eruption of the trans-equatorial coronal arch visible in the first two images. Amazingly, the arch would reshape itself a few hours later and remained visible for another two days!