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Solar Highlights for September 15

Solar Rotation Nos: 2167 to 2169

Solar activity has slowed down a lot now and we are now well past the high levels of activity that we saw throughout most of 2014. There has been a recovery in the level of sunspot activity of late but there are also period of quiet too.

Here are the highlights for September 2015 together with a small selection of images.

A very quiet start to the month and for the much of the first half of September we saw barely any sunspots.

At the beginning of September there were a few small sunspots (often called ‘pores’) but you had to look closely to see all of them. Sunspot group (A)ctive (R)egion2411 came over the (E)ast limb around the 4th but that too was small and easily overlooked at a casual glance. Close behind, and slightly farther south, appeared AR2412, a cluster of mostly small spots. It was AR2414 that had quietly appeared over the SE limb a few days earlier that had a sudden burst of development becoming a type Dao group with two main sunspots on the 12th. However, by this time the group has passed over the Central Meridian (CM) and was rapidly heading towards the (W)est limb, but it was thought to be solar flare active. AR2415 and AR2418 had come over the E limb by the 14th but still the Sun remained quiet, but there were minor flares going off all the time within AR2415.

By mid-September we had four fairly interesting sunspot groups, AR2414 (now near the W limb) and AR2415 (just about to cross the CM), AR2418 and AR2419 (recently over the E limb). Over the next few days we had plenty to see as they were near the centre of the solar disk. By the 20th all the sunspots were now west of the CM leaving the eastern half of the solar disk blank in stark contrast. That was up until the 21st when AR2420 appeared over the E limb followed by AR2421 and AR2422 by the 24th. By the 26th AR2422, on the southern hemisphere, had developed rapidly from a type Eai sunspot group into a type Eko just as it was nearing the CM. Over the next 4 days it continued to grow to become a type Fkc group and produced at least 6 M-class flares by the 30th. It was also in the last week of the September that we saw the highest number of sunspots.

SPA Sunspot Mean Daily Frequency (MDF):  3.75 
SPA Relative Sunspot Number: 64.21

There was at times a bit more to see in H-alpha but just like the sunspot activity in white light, this was mostly seen in the second half of September.

In the early days of the month there were small low-lying prominences especially along the E limb and even when the Sun was almost spotless we saw some plage and filaments on the disk. Ian Lee saw a detached prominence on the S limb on the 5th and saw too that AR2411 had a dark filament close to it.

The 7th saw a rise in activity with some intricate prominences along the E and W limbs and plage and filaments across the disk, some associated with AR2411 and AR2412. By the next day the prominences were confined to the W limb. By the 10th these too had gone and the only feature of note was a small high (possibly detached) prominence on the SE limb, but there were several filaments scattered across the solar disk. Bright plages were seen around AR2412 on the 11th.

Activity picked up again around the 15th as AR2414, AR2415, AR2418 and AR2419 were crossing the solar disk. Plages were seen around all of them and there were some low-lying prominences on the SE and NW limbs. A large hedgerow-type prominence appeared over the SE limb on the 16th and remained visible along the limb until the 18th and was then seen as a broad dusky filament near the SE limb on the 19th. The same filament was then seen crossing the solar disk as the days progressed, reaching the CM around the 23rd. It was still visible on the 28th by then it was near the NW limb and had sunspots below it (AR2423). During this period sunspots AR2420, AR2421 and AR2422 were seen following some distance behind the filament, with extensive plage activity around them. The filament was finally seen as a high and extensively detailed prominence on the NW limb on the 29th and 30th.    
SPA Prominence Mean Daily Frequency (MDF): 4.53   
11  0820UT Flare with AR
      0850UT Flare still there & second flare at E limb
      1030UT Both flares visible
      1130UT Both flares weaker now
      1300UT Both flares look like plages now
17  0800UT Flare with AR2414
      0850UT Flare still visible
20  0810UT Flare at E limb
     1025UT Flare still visible
     1245UT Flare weaker now
30 0820UT Flare within AR2422
     0840UT Flare gone
     0930UT Second flare within AR2422
     0950UT Flare gone, just plage visible now
All the above flares were observed by Alan Heath.

Well done to Brian Gordon-States who observed the Sun on 30 days in September, Alan Heath was close behind on 27 days and Jonathan Shanklin 26 days.

Detailed count records of Active Regions and Relative Sunspot Numbers came from: Richard Bailey, Michael Fullerton, Brian Gordon-States, Alan Heath, Mick Jenkins, Ian Lee, Jonathan Shanklin and Julia Wilkinson.

Images and drawings were supplied by: Richard Bailey, Santanu Basu, Mark Beveridge, Carl Bowron, Paul Brierley, Mick Jenkins, Ian Lee, Cliff Meredith, Mary Spicer and Julia Wilkinson.

Geoff Elston

Solar Section DIrector

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