Solar Highlights for February 18

Solar Rotation Nos: 2200 to 2201

A slight rise in the average number of sunspots (see latest SPA activity graph) and a solar flare active sunspot group mid-month but otherwise plenty of spotless days or short-lived small sunspots.

Here is a summary for February 2018 together with a selection of images made by our observers.

Sunspots:

AR2697 appeared on the last day of January and was by early February just a small southern hemisphere type Axx sunspot at latitude -09°. It had disappeared on the 2nd.

The Sun was spotless for a day on the 2nd.

AR2698 appeared on the E limb on the 3rd. It too was a type Axx sunspot just south of the Sun’s equator, at -03°. It was short-lived and was gone by the 4th.

A large polar coronal hole around the 3rd lead to some high-latitude (Iceland) aurora on the 5th to the 7th.

AR2699 also came over the E limb but on the 5th just south of the equator at latitude -04°. This sunspot was much more active than we had seen previously and was also minor solar flare active right from the start. It was even capable of producing interference on shortwave radio for a while. A minor C-class flare erupted on the 7th at 1347 UT creating shortwave radio interference in the South Atlantic Ocean. Meanwhile the sunspot group was developing in size. It went from type Hsx on the 5th; to type Cso on the 6th; and finally, to type Dso by the 7th and moved slightly further south to latitude -08°. There was another C-class flare on the 10th at 1321UT, though not quite the same strength as previously. The sunspot group reached the Central Meridian (the CM is the imaginary central line between east and west) by the 11th and had changed slightly to a type Dai by then. A coronal hole was see near AR2699 on the same day. However, it was on the 12th, as the four mains sunspots of the group appearing just slightly larger than the Earth were on view, what we could not see was that a C-class flare in AR2699 had hurled a Coronal Mass Ejection (CME) towards us. The after-effects of the CME were more high-latitude aurora around the 15th. As AR2699 headed towards the W limb on the 14th it began to decay away and had vanished by the 18th.

2018 February 7. Image by Carl Bowron.
2018 February 7. Image by Mick Jenkins.
2018 February 12. Image by Cliff Meredith.

The Sun was spotless from the 18th to the 25th when a tiny faint cluster of sunspots were seen near the CM.

AR2700 was the tiny cluster of faint sunspots west of the CM on the northern hemisphere at +06°. It was a quiet group of sunspots (type Bxo) and was still visible by the end of the month.

SPA Sunspot Mean Daily Frequency: 0.59 (was 0.30).
SPA Relative Sunspot Number: 10.30 (was 4.18).

Solar Prominences, Plage, Filaments and Flares

There were some nice but small prominences throughout the month plus the occasional filament on the solar disc. A large, but dim, arch-type prominence was seen on the 12th attached to the north eastern limb and a brighter but somewhat unusually shaped hedgerow type prominence along the southern limb on the 16th. A ‘filaprom’ was observed on the north eastern limb on the 25th.

2018 February 7. H-alpha of solar flare. Image by Carl Bowron.

Without doubt the appearance of AR2699 made a big difference as it produced several filaments and bright areas of plage as the sunspot crossed the Sun. I am amazed at the detail shown in the h-alpha drawings made on the 11th, 12th and 15th by Ian Lee. Quite an achievement!

2018 February 11. H-alpha drawing by Ian Lee.
2018 February 12. H-alpha drawing by Ian Lee.

By late February, there were still a number of prominences to be seen but on some days the solar disc looking quite bland in comparison to the way it looked mid-month!

2018 February 25. Images by Carl Bowron.

SPA Prominence Mean Daily Frequency: 1.92 (was 2.28).

Brian Gordon-States, observed 25 days, Alan Heath observed 22 days, and Jonathan Shanklin 21 days, even while he was returning home to the UK from the Halley Base, Antarctica!

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

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

Geoff Elston

Director