M7.9 solar flare

Thursday, 25 June 2015 18:16 UTC

Strong M7.9 solar #flare from #sunspot region 12371 - Follow live on http://t.co/XHATH0OOfT pic.twitter.com/roltn3J1Ac

— SpaceWeatherLive (@_SpaceWeather_) 25 juni 2015

It was right away clear with the help of SDO imagery that also this solar flare launched a coronal mass ejection, something which was confirmed not much later by SOHO/LASCO imagery. Sunspot region 2371 is now on it's way towards the west limb so it was clear that this plasma cloud wouldn't head towards Earth straight on like the 21 June coronal mass ejection did which produced the severe G4 geomagnetic storm on 22 and 23 June. If we take a look at SOHO imagery (see the animations below) we see a full halo coronal mass ejection but the bulk of this coronal mass ejection is heading well north-west of our planet and will thus miss us. When you look closer you can see that there is a fainter halo outline as well so we can conclude that a portion of the cloud will likely interact with our magnetic field but we should not expect much more than (yes here come those famous words) a glancing blow.

Animations: SOHO/LASCO C2 and C3 animations showing the coronal mass ejection from today's M7.9 solar flare.

CACtus reports that this coronal mass ejection left the Sun at a speed of 1.600 km/sec which is fairly high and the fastest coronal mass ejection launched by this sunspot region. However, this high speed consists of the bulk of this coronal mass ejection that is not coming towards us. The portion of the cloud heading towards Earth is slower as you can see how the halo doesn't expand so fast in the south-east. We estimate this part of the plasma cloud to be around 1.000km/s. Factoring in the high ambient solar wind speed we come to the conclusion that this coronal mass ejection will have a travel time from the Sun to Earth of about 50 hours meaning we can expect an impact time of about 10:00 UTC on 27 June with a plus/minus of six hours. A minor G1 geomagnetic storm will likely follow with a chance for a moderate G2 geomagnetic storm if the direction of the IMF cooperates. The chance for aurora on middle latitude locations is small. A lot will depend on the strength of the IMF and the direction it carries. We have seen before this week how two different CMEs can have a very different IMF strength within them.