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Solar Highlights for September 17


Solar Rotation Nos: 2194 to 2195

A rise in sunspot activity, some naked eye sunspots, and a powerful solar flare contradicted the current overall downward trend of solar activity.

Here are the solar highlights of September 2017 together with a selection of images.


Another month of contrasts. Lots of sunspot activity in the first half, then very quiet. No spotless days were recorded.

1st to 11th September
In contrast to previous months, we saw a lot of sunspot activity in the first half of September. On the 1st we had four Active Regions (AR). AR2672 was at solar latitude N07° and type Dao, AR2673 was south at S08°, and much smaller at type Hsx, AR2674 was N13° (Eho) and AR2675 was S07° and type Dro. AR2674 developed rapidly in a type Fhi by the 2nd. It was AR2673 and AR2674 as the crossed the centre of solar disc from the 3rd to the 5th that appeared to the protected naked eye. AR2673 went through a burst of development around the same time and on the 6th it produced a strong X-class solar flare at 1202UT. On the 7th it produced three M-class flares plus another X-class flare but not of such power as the day before. Sunspot development in AR2673 peaked around the 9th at about this time AR2673 and AR2674 were nearing the western limb. Elsewhere on the disc AR2677, AR2678 and AR2779 were also seen but they were all small.

12th to 30th September
By the 13th AR2673 and AR2674 had gone over the west limb leaving just AR2680. This type Hsx sunspot group was at the centre of the solar disc by the 16th hardly changing in appearance as it headed westwards. It went over the west limb on the 21st leaving AR2681 (type Hsx at S12°) by the opposite limb. It was on the 25th that former group AR2673 reappeared on the east limb, re-designated AR2682 and now decayed to a type Hsx sunspot group. This was followed by AR2683 appearing on the east limb by the 26th. Carl Bowron observed two patches of faculae just east of the north pole on the 28th. As the month concluded, AR2681, AR2682 and AR2683 were seen crossing the solar disc hardly changing.

SPA Sunspot Mean Daily Frequency (MDF): 2.43 (was 1.56).
SPA Relative Sunspot Number: 34.45 (was 23.36).

Solar Prominences, Plage, Filaments and Flares

A decrease in the average number of prominences overall and a period of quiet mid-month but either side of this some very impressive prominences were seen. An upturn in sunspot activity led to more plage and filament activity appearing in hydrogen-alpha. 

1st to 12th September
Quite a lot of filament and plage activity seen on the first few days of the month accompanying sunspots AR2672-2675. The 2nd saw lots of prominence activity. Of note were a tall prominence on the north limb, and an arched type prominence along the south limb. As AR2672-2675 were nearing the west limb on the 9th s number of prominences could also be seen especially a bright detached prominence was seen near the southeast limb. During this period, AR2671-72 both appeared but were short-lived and had disappeared by the 11th. As AR2680 appeared over the southeast limb it was followed by another tall prominence and a particularly impressive arch prominence on the 11th. Both seemed to disappear by the 12th.

13th to 21st September
Within AR2680 the sunspot umbra appeared to have fully split into two separate spots by the 14th. No further development activity was seen after that but there was the appearance of a broad dark filament east of AR2680 on the 19th. Fewer prominences were recorded during this period.

22nd to 30th September
AR2681 as it came over the east limb, brought with it several plages and filaments and a complex hedgerow prominence along the limb on the 23rd. With the appearance of AR2681 and AR2682 the whole SE limb region was seen to have plage and filament activity with prominence activity along the east limb. This activity remained in the following days and by the end of the month we had plage and filament activity around AR2681 and AR2682 plus numerous prominences around the solar limb, especially the west limb.

Alan Heath reported the following solar flares:

6th  0710UT 2 flares with the p. AR (2673) both very bright. 1450UT Flares still there.
7th  0800UT Flare with p.AR (2673) which covers most of active region. Intensely bright. I am told this was X-9 flare. 

SPA Prominence Mean Daily Frequency (MDF): 3.23 (was 3.51).

Well done to Brian Gordon-States, who observed 30 days, to Alan Heath for 26 days. Also to Jonathan Shanklin and Bob Steele for achieving 25 days and 23 days respectively.

Detailed count records of Active Regions and Relative Sunspot Numbers came from: Brian Gordon-States, Michael Fullerton, Alan Heath, Mick Jenkins, Ian Lee, Lee Macdonald, Jonathan Shanklin, Bob Steele and the Director.

Images and drawings were supplied by: Carl Bowron, Alan Clitherow, Mick Jenkins, Ian Lee, Cliff Meredith and Julia Wilkinson.

Geoff Elston


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