Harry lists the super flares of the current solar cycle 24 and hopes for more

SC24FlaresGraph

Flares stronger than class X1 during the current solar cycle plotted as bars. Some have been shifted a little to avoid overlapping. Sketch and copyright Harry Roberts ©, all rights reserved

Witnessing a ‘great’ solar flare is one of astronomy’s rare ‘treats’: they are uncommon at any time – and seeing one is a revelation!

If we define ‘great’ as any flare stronger than GOES X-ray class X1, there have been (as I write) only twenty-seven since solar cycle 24 (SC24) began five years ago.

Flare classes: There are five classes in the GOES system: they are A, B, C, M and X (for ‘extreme’?), each divided into steps 1 through 9, and class X describes any flare whose x-ray flux exceeds 10^-4 watts/m^2 at the satellite’s detector – the other classes are powers of ten weaker.

Flares are so hot they emit mostly in the x-ray band, and that flux is a good measure of total flare energy. In H-alpha they appear as irregular areas that brighten in a minute or so to at least twice the background brightness – often many times brighter. Most occur in sunspot groups.

Spot complexity. Class X flares occur in sunspot groups that have both strong magnetic fields and magnetic ‘complexity’. This ‘complexity’ may arise in various ways, usually when a new sunspot pair (or two) emerges within an existing group – particularly if one pair has its polarity reversed from normal. Field ‘helicity’, or degree of ‘twist’, plays a big role too – and the rearrangement or ‘reconnection’ of complex fields is what drives all flares.

These precursor events are uncommon, so ‘great’ flares occur only in brief periods during any solar cycle.

SC24 events. In SC24 the 27 X-class flares (so far) are ‘clumped’ into just a few short bursts of activity. Let’s consider events, year by year, since X-class flaring began in 2011. The graph, Fig 1, shows the SC24 flares >X1 plotted as bars, ‘shifted’ a bit to avoid overlapping.

2011. That year saw the first X-class flares of the new cycle (SC24) in February/March, with one each in AR11158 and 11166. Later that year, in August/September, we had a cluster of six X-class flares: one, an X6.9 in AR11263, was the strongest so far, with three lesser ones in the same group.

2011 had eight ‘great’ flares: a good start to SC24 flaring and hinting at stronger ones to come.

2012. Despite 2011’s strong start there were just seven class-X flares in 2012 though one, an X5.4 in AR11429, was second strongest of SC24 so far – with two lesser ones in that group also. The other four of 2012 were all 2013. Now most of the way through 2013 we have, so far, had 12 class-X flares: a big rise over earlier years.

flare_loopsX3_AR11748

Post flare loops associated with sunspot group AR11748. Sketch and copyright Harry Roberts ©, all rights reserved

The first four were in AR11748 (mid-May), when the writer managed to log an X3.2 (strongest of 2013). Fig2 shows post flare loops above this sparse group, with its odd mix of fields. It had three more class-X flares in the range X1.2 to 2.8 over just three days.

The next most active spot group to host ‘great’ flares in 2013 was AR11890 that unleashed an X3.3, third strongest for the cycle and two X1.1 flares in November. The other ‘great’ flares of 2013 were the product of three separate spot groups. As the plot at the top shows activity was ‘clustered’ in May and in Oct/Nov.

November’s flares were mostly in southern spot groups – suggesting the southern hemisphere is playing ‘catch-up’ to northern activity that dominated in 2011 and 2012.

Trend. So far in SC24 the strongest flares were all in northern sunspots with an X6.9 and X5.4, while southern groups are yet to host a flare stronger than X3.3. No upward trend in the power of class-X flares is, as yet, seen (Fig1) – but with few such events, caution is needed: history suggests a rise in coming months.

Perhaps the last days of 2013 will unleash a ‘storm’ – not of bushfires we hope – but of X-class flares, under Australian summer skies. Remember, class-X flares are rare and always unexpected!

Harry Roberts is a Sun and Moon observer, a regular contributor to the Sydney Observatory blog and a member of the Sydney City Skywatchers.

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6 responses to “Harry lists the super flares of the current solar cycle 24 and hopes for more

  • I have been trying to find out what effect a great x class will have on Australia. Everything I come across tends to say “wipe out power across the US”, but nothing about Australia. So, merely as a matter of interest, does anyone know what will happen here? I know internet and mobile phone could be lost, but what about power? And would it affect the whole country or just parts?

    • Hello Gayle. Australia would not be immune to the effects of a large geomagnetic disturbance, but its large distance from the Earth’s magnetic poles should reduce any impacts on its power supplies. The last period of strong geomagnetic activity, in late 2003, did have some consequences for Australia – see this article from the the Bureau of Meteorology’s Radio and Space Weather Services.

      • Hmm, thanks Nick. I am not sure whether to be relieved or disappointed. The thought of the world going back in time and slowing down for a while is quite appealing.

  • How long from wow to gone 🙂 does a flare on average take?
    can i shoot one with a 400mm camera lens with a 400 or 9 stop filter and 22 plus f/stop plus 1/8000 ss
    is it possible?

    • Hello keith. A flare typically lasts an hour or so, but white light flares are very rare. Harry would see more as he uses a hydrogen alpha filter. To photograph the Sun you would need a suitable solar filter – available from telescope shops or make your own using Baader solar film eg from http://www.ozscopes.com.au/baader-astrosolar-safety-film.html. Once you have an appropriate solar filter you should take lots of practice shots of the Sun and check the appropriate websites to find out when a major flare is happening. Above all be careful as the Sun can permanently wreck your vision as well as destroying your camera if you are not careful.

      • Thankz Nick , have shot E clipse, with the setting previously given, my attack is auto focus off have previously set to infinite, then up click off probable no more than 1/2 a second duration .
        will check out your suggestions …
        thanks again ..

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