Monthly Archives: December 2015

More transatlantic aurora

On the 17th December, shortly after 09z, there were two solar coronal mass ejections (CMEs) in rapid succession, both of which directed at least some of their ejecta towards the Earth. This was fair warning of the possibility of aurora due some time on the 19th, depending on exactly how fast the material was traveling. The strength of any aurora would also depend on the alignment of the Interplanetary Magnetic Field; for maximum effect we would need a strong southerly component.

As anticipated, the CMEs passed the ACE spacecraft at 13:05z on the 19th, hitting the Earth approximately one hour later. The good news, from our point of view, was that the IMF had a significant southerly component for much of the time, resulting in excellent coupling of the CMEs into the Earth’s magnetic field causing a nice strong aurora!

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