Basically what happens when a CME arrives near Earth is a more dramatic example of processes that happen all the time - but on a larger scale and with a lot more energy. In fact, it's the magnetic fields that are important. The Earth has one, like a great big bar magnet, and the CME has one which it inherits from the Sun when cast out into the wilderness. So when a CME like this one, which is directed at the Earth, finally gets here, the two magnetic fields crash into each other, and that's when interesting stuff happens.
Magnetic fields are basically solitary beasts and don't like to interact with others. Sometimes though they're forced to, and when they do it can result in the release of stored magnetic energy which in turn does other things like accelerate particles. The particles in the CME are essentially all protons and electrons, and these are easily accelerated to high speeds and energies within the Earth's magnetic field. Like in the bar magnet - remember the school experiment with iron filings? - most of the Earth's field is closed apart from at the poles, so the energetic CME particles get injected into the polar regions.
These accelerated particles then travel down towards the Earth's surface and when they get to a certain altitude they collide with atmospheric particles, normally nitrogen and oxygen. When you get a particle collision like this you have another release of energy, in the form of light at a particular energy - and therefore colour. There are only a certain number of combinations - electrons and protons hitting oxygen and nitrogen - so tyypically four interactions, energies and colours. That's why the aururae are normally shades of green or red.
This whole process happens all the time at the boundary between the Earth's magnetic field and the solar wind. The solar wind is always there carrying a pretty uniform mixture of protons, electrons and a tiny remnant of the Sun's magentic field out throughout the solar system and beyond. The magnetic process I've outlined above happens rather frequently, but at much lower energies so that the accelerated particles don't make it down far enough to generate aurorae. The CME can be thought of as a great big cloud within the solar wind, and it forces stuff to happen due to the larger energies involved. It's a bit like a thunderstorm passing overhead - it's all part of the the overall climate and weather system but a very energetic and disruptive part. It's inherently transient, though, so it rages like hell for a bit and then blows over.
So that's it in a nutshell! Next lessons: radiation belts and why there's no life on Mars, then particle accelerators and why the LHC is so damn expensive.
No, I'm, not Brian Cox, though I did study at Manchester University at the same time as him.
Cheers, Gareth.
f0rd":12am68dd said:
orange71":12am68dd said:
a large coronal mass ejection heading in the direction of Earth at a speed of 93 million miles which might hit on Tuesday or Wednesday
?? the sun is at a distance of 93 million miles, at the speed these things travel it would arrive a lot sooner than that I would have thought?
I think and I could be wrong on this, the solar wind the interacts with the atmosphere isn't made up of photons, but electrons and protons so when this storm happens they get flung out, but because they have mass they can't travel at the speed of light.
Thought it was something else
