Northern lights

[BC Mike]

The news this morning told me the magnetic field is moving and the Northern lights normally seen in Canada may shift to Siberia.
I know the magnetic field shifting is old news but this is the regular news, and nothing is news until they report it. We get lots of tourists, mainly Japanese comming to Canada to view the lights. But, how come they have Northern lights, Southern version in Antartica, if the magnetic field is in the North.
I thought it was the suns rays going past the ends, top and bottom, and interacting with our earth particles at the appropriate angle. So what does the magnet have to do with it?
We get them at 49 1/2 degrees North but not as often as places further North.
Michael

[delmarrey]

Aurora is now known to be caused by electrons of typical energy of 1-15 keV, i.e. the energy obtained by the electrons passing through a voltage difference of 1000-15,000 volts. The light is produced when they collide with atoms of the upper atmosphere, typically at altitudes of 80-150 km. It tends to be dominated by emissions of atomic oxygen--the greenish line at 5577 A and (especially with electrons of lower energy and higher altitude) the dark-red line at 6300 A. Both these represent "forbidden" transitions of atomic oxygen from energy levels which (in absence of collisions) persist for a long time, accounting for the slow brightening and fading (0.5-1 sec) of auroral rays. Many other lines can also be observed, especially those of molecular nitrogen, and these vary much faster, revealing the true dynamic nature of the aurora.

Aurora can also be observed in the ultra-violet (UV) light, a very good way of observing it from space (but not from ground--the atmosphere absorbs UV). The "Polar" spacecraft even observed it in X-rays. The image is very rough, but precipitation of high-energy electrons can be identified.
The curtains often show folds called "striations." When the field line guiding a bright auroral patch leads to a point directly above the observer, the aurora may appear as a "corona" of diverging rays, an effect of perspective.

In 1741 Hiorter and Celsius first noticed other evidence for magnetic control, namely, large magnetic fluctuations occurred whenever the aurora was observed overhead. This indicates (it was later realized) that large electric currents were associated with the aurora, flowing in the region where auroral light originated. Kristian Birkeland (1903) deduced that the currents flowed in the east-west directions along the auroral arc, and such currents, flowing from the dayside towards (approximately) midnight were later named "auroral electrojets." (see also Birkeland currents).

Still another evidence for a magnetic connection are the statistics of auroral observations. Elias Loomis (1860) and later in more detail Hermann Fritz (1881) established that aurora appeared mainly in the "auroral zone," a ring-shaped region of approx. radius 2500 km around the magnetic pole of the Earth, not its geographic one. It was hardly ever seen near that pole itself. The instantaneous distribution of aurora ("auroral oval," Yasha Feldstein 1963) is slightly different, centered about 3-5 degrees nightward of the magnetic pole, so that auroral arcs reach furthest equatorward around midnight.

Aurora is a common occurrence in the ring-shaped zone. it is rarely seen in temperate latitudes, usually only when a big magnetic storm temporarily expands the auroral oval. Large magnetic storms are most common during the peak of the 11-year sunspot cycle, or during the 3 years after that peak. However, within the auroral zone the likelihood of aurora depends mostly on the slant of interplanetary magnetic field lines (further below), being greater with southward slant.


http://www.gi.alaska.edu/cgi-bin/predict.cgi

[NoTies]

Yeah, what Delmarrey said
Down here over winter the lights are very common and at the elevation of the south pole they can be heard at times as well.
We only ever get to see the green colouring here but on the odd occasion I have seen them from the south of NZ they have been quite a range of colours. Any idea why?

[2divers]

pwederell once whispered in the wind:
Yeah, what Delmarrey said
Down here over winter the lights are very common and at the elevation of the south pole they can be heard at times as well.
We only ever get to see the green colouring here but on the odd occasion I have seen them from the south of NZ they have been quite a range of colours. Any idea why?

You can hear them? I've spent time on the US border w/ Canada, but I've never heard someone say that you could hear them before! Thought would be so Awesome! Have experienced this? What does it sound like?

[CaptainK]

There has been a recent occurance. Say within the past 10 years. Can not remember what year it was? But the Northern lights were seen as far as the upper northeastern US.

They say it's due to the solar radition hitting the magnetic belt that surrounds the earth. And then we get to see it down here on the ground as the Lights. And then you add the technical terms that delmarrey used in his post. To further the techno specifications on whats really going on around our planet.

[ssullivan]

I've seen them in southern NH on a number of occasions.

Del, did you work on any of the Solar Terrestrial Phyics missions? I'm curious... sound like you may have a background in the field. Maybe we know some of the same people. I have worked on the CLUSTER, FAST, and ACE missions for NASA/ESA.

[NoTies]

2divers, unfortunately I haven't had the experience myself but have spoken to many "Polies" who have. The elevation at South Pole is around 10000' so this may account for it. Us coast dwellers miss out on so much.

I saw them once up in Whitehorse. It was an incredible experience. For me, the desire to know why they occure has just never been a priority. They are something much more than their science. Kinda like green flash sunsets. When you are watching it, who cares why it happens. I am fascinated by the why of allot of things, but some are just magical regardless of why they occure.

[Alan Wheeler]

I saw the Southern one when I was a Teenager. I was living in the central area of our SouthIsland. Probably 43'ish South. It was like a huge curtain blowing in the wind of all these changing colours. Truely beautiful.
Pete, one of the reasons why you don't see it well really close to the magnetic pole, is the plasma is densly following the lines of magnetic flux of the earth as it draws down to the pole. It's dense and you don't see the shift in colour quite the same. The shift iin colours accours as you get further away towards the fringe of the activity. The colour is mainly to do with the particular gases being Ionised. Mostly oxygen.
Once again, I am just being ruff with this. It can get complex just as Delmarrey has shown, and he has done a good job anyway.

One question I do have, and if there are any scientist that work in this feild down there with you, maybe you could ask.
Just how close to ground level does this stuff actually come as it follows the lines of magnetic flux. I realise it is still high altitude, but?

[BC Mike]

One thing we have in the North to check the angle of the dangle is the North Star or pole star. It is close enough to being directly above the North Pole. It makes for an easy reference for telling how far away we are from the North Pole. You need an anglemonitor in your head to do this but I hope you get the picture. Driving home after a party on Saturday night, it can be quite distracting having those funny lights going off all around. You about have to stop and grab something solid. A bit like sailing.
Michael

[delmarrey]

ssullivan once whispered in the wind:
Del, did you work on any of the Solar Terrestrial Phyics missions? I'm curious... sound like you may have a background in the field. Maybe we know some of the same people. I have worked on the CLUSTER, FAST, and ACE missions for NASA/ESA.

No! Actually, I cannot take credit for the statement above I copied it off a site that I've picked up along the way as an information junky. Although, I did want to work for NASA years ago. My closes experience is actually living in Alaska and enjoying the awesomeness (is that a word) of it all.

As well, up there, there are shooting stars (meteorites), which are very common. Any place that lacks the city lights and noise, like within the artic circles, will display the beauties of the hemisphere............._/)