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Thursday, February 17, 2011

Storm or no storm?

Solar flares and the possibility of seeing the Aurora Borealis over the UK have been in the news today. It stems from the fact that on Tuesday (at about 2am) we had the biggest solar flare that we have had for something like 4 years. It was what we call an X-class X-ray flare. that means the energy flux was greater than 0.001 Watts per square metre. You can see the recent flare on the plot below, which is courtesy of the excellent Space Weather Prediction Center, part of NOAA.



From the right-hand scale you can see it tipped over into the X-class band and it was what we would call an X2 flare.

Associated with this flare was a CME - a coronal mass ejection. This big magnetic cloud is currently travelling through interplanetary space and our best guess is that it is heading straight towards Earth. If and when it hits it could trigger a geomagnetic storm. If the CME has a large southward magnetic field component it might lead to conditions ripe for aurora over mid-latitudes (i.e. the UK).

Note the important words in italics.

It is great that the Sun is being active again as we head up towards the next solar maximum. The long solar minimum was pretty geophysically interesting but at the same time its nice to have a chance of seeing aurora at mid-latitudes; and chances of doing so do go up at solar max.

Clearly it is nice that the aurora is getting a mention in the media but I have been a leeetle bit concerned about some of the coverage. I am concerned (rightly or wrongly) that the impression is that we will see some aurora. To be sure this is the best chance for quite some time and it is an encouraging event but it is not a foregone conclusion. For example take the title of this BBC news story

Aurora Borealis to light up the night sky

The story itself is a bit more balanced but the headline is worrying. On the other hand, here is a really good, balanced story by Paul Rincon, also on the BBC.

Now as of yet the CME from the X2 flare has not hit and so the chances for aurora viewing are still there and still reasonable. Though if it hits in the morning, as solar storm watch predicts, we have to hope that the auroral oval stays at mid-latitudes for quite a few hours.

This may be a bit of a tall order.

Postscript: it is not a strictly linear relationship but it is worth bearing in mind that the last time aurora was visible over the north of England it followed an X7 flare. So I suspect that the best place to see aurora in the UK will be Scotland and Northern Ireland.

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