A compilation of the most memorable space weather moments of 2011 can be found underneath. Using the fantastic (J)Helioviewer software, a ***MOVIE*** was created containing one or more clips of each event. Usually, images obtained by SDO, SOHO, , and the STEREO spacecraft were used, occasionally supplemented by imagery from the PROBA2 satellite.
This is a chronological list of punctual events on or near the Sun, and thus does not contain items such as the last flight of the Space Shuttle (21 July), the press event on the "Sun-to-Earth" tracking of the December 2008 CME (18 August), and the re-entry of the UARS (23-24 September) and ROSAT (23 October).
In 2011, solar activity finally shifted into a higher gear, with 111 M-class flares, 8 X-class ("eXtreme") events and several major to severe geomagnetic storms. The activity occurred essentially on the northern solar hemisphere. A (first) maximum of the ongoing solar cycle seems to have been reached around year's end.
We hope you enjoy the movie clips and the brief summaries!
The first X-class flare of the new solar cycle (SC24) is a fact. It was the first "eXtreme" event since the X-class flare on 14 December 2006, 1524 days ago - an absolute record since measurements started in 1976. The X2.2 flare peaked at 01:56UT and was produced by complex active region NOAA 1158, of which the sunspots showed a prominent helical movement. The associated full halo coronal mass ejection (CME) caused only a minor geomagnetic storm on 18 February due to its mainly northward oriented magnetic field. NOAA 1158 was also one of the most flare productive regions in 2011, producing 56 C- and 6 M-class flares during its transit.
An impressive solar eruption took place near the east solar limb during the morning hours of 24 February. It was associated with an M3 flare and a coronal ("EIT") wave. The source region was the relatively small and simple sunspot group NOAA 1163, which would produce only a few more C-class flares after this medium flare. The eruption was essentially a "cool" event, being only well visible in the "colder" wavelengths of AIA304 (about 80.000 degrees), and was much less spectacular in the hotter wavelengths such as AIA171 (700.000 degrees) or AIA 094 (several million degrees).
The year 2011 will especially be remembered for a jaw-dropping event that took place on 7 June. Around 06:15UT, the filament in the small sunspot group NOAA 1226 got unstable and was ejected into space. Amazingly, a huge amount of the material fell back to the Sun in a fountain-like way, prompting a NASA/GSFC solar physicist to compare it "... as if someone kicked a clod of dirt in the air ...". Very "cold" plasma (dark; about 20.000 degrees) could be seen crashing unto the solar surface for about 4-5 hours, often several hundreds of thousands of kilometers from the blast side. The Humain Solar Radio Observatory recorded a Type II radio burst, and the SWAP telescope onboard the PROBA2 satellite imaged the blast in extreme ultraviolet (EUV). The eruption was also associated with a coronal wave ("solar tsunami"), an M2 flare, a minor proton event and a fast CME (1100 km/s) that skimmed the Earth's magnetosphere late on 9 June, not causing any significant geomagnetic activity.
Ref: STCE news item of 9 June 2011
Early August, 3 prominent sunspot groups embellished the Sun's northern hemisphere. Using eclipse glasses, some solar observers even reported them as visible to the naked eye. NOAA 1261 (the "middle" group) was the most active region, producing several M-class flares during its transit. Around noon on 3 August, it produced an M6 flare followed early on 4 August by a powerful M9.3 flare. The associated halo CMEs were earth-directed and had speeds of resp. around 800 km/s and over 1500 km/s. Hence, the first, slow CME was overtaken by the second, much faster CME en route to Earth. This fine example of "CME cannibalism" resulted in a complex structure with a strong southward oriented magnetic field (-20nT). A severe geomagnetic storm was recorded on 5-6 August (Kp = 8 ; Dst = -115nT), with aurora being reported from as far south as England, the Netherlands and northern Germany. Of note is also that the M9 flare was a rare night-time radio burst, and that it was associated with the strongest proton event of the year (96 pfu, still a minor radiation event).
Ref: STCE news item of 6 September 2011
Starting early on 6 August, new magnetic flux emerged near the trailing portion of NOAA 1263, i.e. the "left" (most eastern) region of the aforementioned sunspot trio. Gradually, the leading portion of this newly emerging flux engulfed the opposite polarity trailing portion of NOAA 1263. After producing a few minor M-class flares on 8 and early on 9 August, the magnetic delta configuration finally released a major X6.9 flare on 9 August peaking at 08:05UT, briefly disrupting VLF and HF radio communications. So far, this flare is still the strongest of the ongoing solar cycle 24. A small proton event (26 pfu) was recorded. The bulk of the associated CME was directed away from the Earth.
Ref: STCE items of 9 August 2011 and 6 September 2011
NOAA 1283 was a rather small but compact sunspot group with a delta north of its main spot. It was the first of only 2 groups to produce 2 X-class flares during their transit over the solar disk in 2011. An X2.1 flare was produced late on 6 September, followed by a truly spectacular X1.8 event about 24 hours later. The associated CMEs caused major geomagnetic storming on 9 and 10 September. Bright aurora were observed for more than 18 hours!
NOAA 1302 was the first super group of SC24, totaling 7 times the total surface area of the Earth. This complex sunspot region was the most flare active group of 2011, releasing no less than 17 M-class and 2 X-class flares. In particular the first extreme event, a long duration X1.4 proton flare on 22 September, provided astonishing EUV imagery as NOAA 1302 rounded the east limb. The other X-class event (X1.9) as well as numerous M-class flares on 24 and 25 September were associated with earth-directed CMEs. As a result, a severe geomagnetic storm (Kp = 8 ; Dst = -118 nT) on 26-27 September and more minor storming a day later. The series of consecutive CMEs temporarily reduced the cosmic rays arriving at Earth, and a Forbush decrease of 5.5% was recorded by neutron monitors on Earth (Oulu NM ; 5 min. data).
Another episode of major geomagnetic storming (Kp = 7 ; Dst = -147 nT) took place on 24-25 October. The most likely source of the responsible CME seems to have been a filament eruption in the northwest solar quadrant early on 22 October. However, also the CMEs associated with the M1.3 eruption in NOAA 1319 on 21 October (peak at 13:00UT) and especially the long duration M1.3 flare in NOAA 1314 on 22 October (peak at 11:10UT) could have contributed. Space weather effects were numerous. The Earth's magnetic field got so compressed that geosynchronous satellites were briefly exposed to the solar wind. Geomagnetically induced currents were recorded in Scandinavia, and a Forbush decrease of 5.5% was recorded by neutron monitors on Earth (Oulu NM ; 5 min. data). The storm will especially be remembered for its blood red aurora, some of which were seen as far south as Oklahoma and Arizona, as well as in New Zealand and in Australia.
The highest monthly sunspot numbers are recorded, with 13 sunspot groups visible on 14 November. We have to go back all the way to 2002 to find even higher sunspot numbers. Also the total sunspot area is highest (9 November), as are the number of observed CMEs (several important eruptions every day). The source of most of the activity during the first half of the month is NOAA 1339, the largest sunspot group and second super group of the year. The region has an area equivalent to 9 times the surface area of the Earth, and produces the last X-class flare of the year. Some of the CMEs were related to backside activity, but also filament eruptions contributed, notably with an eruption on 9 November, and the partial eruption of a 1 million km (!) long filament on 14 November. The remaining part would fully blow itself into space on 23 November. Interestingly, all this (frontside) activity did not result in strong geomagnetic disturbances.
As a general rule, comets that come too close to the Sun won't live to tell. Not so for comet Lovejoy, surviving a kiss-and-ride only 140.000 km above our star's scorchingly hot surface. Following this close encounter, it would go on and become a naked eye comet for observers on the southern hemisphere, one of the brightest comet displays in years. The trip through the Sun's corona on 15-16 December was observed by no less than 6 spacecraft (SDO, SOHO, PROBA2, the two STEREO spacecraft, and HINODE). Detailed imagery revealed the comet's wiggling tail as it apparently interacted with the corona's magnetic structures. Hence, the observations resulted in numerous papers (see e.g. here, here and here) contributing to a better understanding of the Sun's atmosphere.
Ref: STCE news item of 16 December 2011