Aurora and the colour red.

[Richard_Healy]

I'm writing an article on the 1859 event of a direct hit on Planet Earth of a solar flare, triggering aurora all across the North Hemisphere, observed as far south as Cuba (!) and Rome (!!)

 

http://science.nasa.gov/headlines/y2008/06may_carringtonflare.htm

 

So I'm reading through the archive of the American Science Journal for 1859-1860, which contain the direct observations from countless astronomers and observatories across the August 28th - Sept 2nd period when the Aurora were at their maximum.

 

http://diva.library.cmu.edu/ajs/browse.jsp?n1=6

 

And something jumps out at me from all the various reports - the predominance of the colour red in the prominence and curtains.

 

Aurora we all know operate a bit like the gas in a neon tube - the gasses in the atmosphere glow when they are excited, the magnetic field lines funnel charged particls towards the poles and - hey preto - the atmospheric gasses glow all sorts of colours.

 

What I wanted to know was why was there so much red?

 

I did a little digging and found this website:

 

http://ffden-2.phys.uaf.edu/211.fall2000.web.projects/Christina%20Shaw/AuroraColors.html

 

Which says all red aurora is Oxygen, higher than 200km and Crimson colouration is neutral Nitrogen below 100km.

 

Green being the most common colour seen, what I was wondering was this - did the extremely high energies involved in the Super-flare event (as oppose say normal solar winds) have anything to do with either a) exciting oxygen at high altitudes than normal or b) exciting neutral Nitrogen at lower altitudes than normal.

 

I accept red auroras are fairly common - one of the many ways this event is unique seems to be the distribution of auroral effects and the near universal agreement on the structures, colours and position (everywhere!)

 

I only registered today with the sole purpose of finding out more about this so can anyone help me?

 

 

Thanks.

 

 

Richard.

[insane_alien]

the only thing non-standard about this is that it distorted the magnetic field enough to be seen that far south.

 

colour generation would be exactly the same as usual though.

[Richard_Healy]

Thanks for describing the distortion to the magnetic field - that makes sense. As I've been reading, the aurora were seen as far south as El Salvador and Guadeloupe! This was some distortion!

 

Something I'm still not clear on though - if, granted the mechanism for colour generation doesn't alter , and that I've described it accurately above - why was there *so much* red and not, say green?

[Richard_Healy]

Anyone?

 

Why such a predominance of red in the aurora that encircled the globe? It is mentioned by nearly every eye-witness statement I can find.

 

That's a little odd isn't it? I'm sure the mechanism is the same I'm just perplexed why the apparent uniformity of colour was reported.

 

Thanks.

 

RH.

[insane_alien]

i have no idea of the specifics of it, but it is elementary to deduce that it is because it is only interacting with oxygen.

 

why it does not induce green light from nitrogen i do not know. but this isn't exactly a rare condition as i have seen aurora that are almost completely red and almost completely green.

 

i'm sure someone can answer your question but perhaps it isn't here(judging by the lack of responses)

[Richard_Healy]

Thanks for getting back to me IA.

 

Mmm....I was hoping I'd find an answer here, guess not.

 

I was just curious is all, why the interaction with Oxygen would be so predominant the world over - it is after-all not the most populous gas.

 

I'm assuming it's something to do with the interaction and the altitude of the atmosphere where the storm is taking place but now I'm just speculating.