So why all the fuss? Well, let’s start at the beginning...
|An image of the Sun from the Solar dynamic|
observatory during the X-class flare (the bright
area near the centre) on 7th Jan.
Given all that information most forecasters (including us here at the BGS) were in agreement that this CME was very likely to hit the Earth’s magnetic field at some point on the 9th January. When a CME arrives at Earth we expect to see a shock signature observed in the ACE satellite data. This means we see a sharp jump in the velocity and magnetic field of the solar wind – which is a continuous stream of charged particles released from the Sun.
Sure enough, just after 19.00 on the 9th the shock arrived, so the CME had arrived – time to get excited (and tweeting). However, to get a geomagnetic storm, and therefore the Northern lights there are a few more complications....
Firstly, the CME had arrived several hours later than expected suggesting it was a bit slower than first predicted - in general the faster the CME the bigger the resulting geomagnetic storm. Secondly, the shock was also quite small which might mean that we only received a glancing blow from the CME, and most of it missed us. Thirdly, and most importantly, to get a geomagnetic storm a CME really needs to cause the interplanetary magnetic field (the field trapped in the solar wind – or IMF) to turn southwards, which allows much more energy into the Earth’s magnetic field. Following last night’s CME arrival the IMF stayed stubbornly northwards, therefore, the geomagnetic storm never really got going.
In short, space weather forecasting is really hard! We are continuously improving the way we forecast and model space weather, but until we can get more information about the CMEs before they reach us there will always be a lot of uncertainty.
To get daily space weather forecasts follow @BGSspaceWeather and for those all important aurora alerts follow @BGSauroraAlert.
Flares are caused by the explosive reorganisation of magnetic fields in the Sun’s atmosphere, and are classified according to how powerful they are as A (the least powerful), B, C, M or X (the biggest). X-class flares are the most powerful, ranging from X1 up to at least X28, where an X10 is 10 times more powerful than an X1.
‘Space weather’ is a term to describe the conditions in the space between the Sun and the Earth. Changes in space weather are almost exclusively driven by events on the surface of the Sun, and the Sun’s atmosphere.
To find out more on the science of geomagnetism go to our website here.