Space weather highlights for May 07 – May 13, 2012: 55 C-class and 6 M-class flares


Solar activity ranged from low to moderate levels. Region 1476 (N10, L=180, class/area=Fkc/1050 on 09 May) was responsible for almost all x-ray flare activity during the week. It produced a total of 55 C-class flares, 6 M-class flares, and 69 optical flares.

Region 1476 began the week as an Fkc type group with a beta-gamma magnetic configuration. By the 8th, it had grown in extent (17 degrees), spot count (35), and complexity (beta-gamma-delta) and produced an M1/1F flare at 13:08 UTC. It reached its maximum areal coverage of 1050 millionths on the 9th when it produced an M4/1n at 12:32 UTC, an M1/1b at 14:08 UTC, and another M4 at 21:05 UTC.

The maximum extent and spot count (20 degrees, 50 spots) followed on the 10th when Region 1476 produced the largest of the flares, an M5/2b at 04:18 UTC.

The flare was accompanied by a three minute 10cm burst (690 sfu) at 10/04:17 UTC and a Type IV emission at 10/04:02 UTC, followed by a weak earth-directed Coronal Mass Ejection (CME).

Later that day, Region 1476 produced an M1 at 20:26 UTC, the last M-class event of the week.

The region then began a slow but steady decline in areal coverage, longitudinal extent and spot count, although it sustained its beta-gamma-delta magnetic configuration.


Earlier in the week, the only M-class event not produced by Region 1476 was an M1/1n flare observed from Region 1471 (S21, L=276, class/area=Eho/320 on 02 May) at 07/14:31 UTC. This flare was also accompanied by a 10cm burst (230 sfu) at 10/14:15 UTC and a Type IV emission at 07/14:09 UTC.

STEREO-Ahead imagery suggested an earth-directed CME. The following day, two more potentially earth-directed, weak CMEs were observed in STEREO-A COR2 imagery.

Region 1477 (S24, L=140, class/area Dso/150 on 09 May) was split to form new Region 1478 (S24, L=135, class/area=Hsx/090 on 10 May) on 10 May. Similarly, Region 1479 (N15, L=105, class/area Dso/130 on 12 May) was split to form new Region 1482 (N14, L=100, class/area=Dso/080 on 13 May). Both of these divisions resulted from careful analysis of magnetogram data. After the split, Region 1477 became an Hsx type group with L=144, and Region 1479 became an Hxs type group near L=109.

No proton events were observed at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit was at high levels on the 10th through the 13th, and at moderate levels for the remainder.

Geomagnetic field activity ranged from quiet to active conditions with minor to major storm periods observed at high latitudes. The week began with quiet conditions on 7th and the majority of the 8th. Around 08/04:00 UTC, a solar sector boundary crossing from positive to negative was observed at the ACE spacecraft. By midday, the solar wind speed at ACE began to rise, marking the arrival of a coronal hole high speed stream (CH-HSS). Significant southward Bz began around 17:30 UTC and reached a minimum of -13 nT late on the 8th before beginning a gradual return to neutral conditions late on the 10th. The geomagnetic field responded with active conditions from the last synoptic period on the 8th through the 9th. Minor to major storm levels were observed at high latitudes on the 9th.

Activity subsided to mostly unsettled levels on the 10th, followed by mostly quiet conditions on the 11-12 May. The solar wind speed at ACE remained above 500 km/s until around 13/00:00 UTC. Conditions were mostly unsettled on the 13th. Although there were a number of CMEs identified as potentially earth directed, there was no definitive indication of CME arrival reflected in the ACE data suggesting the transient signatures were obliterated in the high speed stream.

Source: swpc.noaa.gov

Featured image: SDO AIA 193 on May 10, 2012 at 04:18 UTC – M5.7

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