Talk: Northern Lights ASCII (180 lines)

In article <3ekdtp$33...@gagme.wwa.com> ric...@isl.uit.no (Curt Rice) writes:
>
>In article <3ehvm2$sp...@gagme.wwa.com>, jit...@erehwon.caltech.edu (Mike
>Jittlov) wrote:
>
>
>[much deleted]
>> Crosspost/imported from:
>>
>> rec.arts.ascii (moderated) #3503 (6 + 19 more)
>> From: ric...@rs4.tcs.tulane.edu (Dave Rice)
>> [1] Line: Aurora borealis/Northern Lights
>> Date: Fri Dec 30 20:21:39 PST 1994
>> Organization: Tulane University, New Orleans, LA
>> > A few comments on aurora and on the figure:
>>
>> Aurora borealis and its southern counterpart, aurora australis, are phenomena
>> that occur only in the high latitudes, about 65 degrees North or South.
>
>> The glow is not terribly bright, in general.  Thus the glow is seen usually
>> under conditions of low ambient light from other sources.  This means that
>> the sightings are mostly in winter, because it is light all the time in the
>> summer at high latitudes.
>
>>
>> Most auroras are diffuse greenish-white clouds.  These are not so interesting
>> because they resemble clouds lit by moonlight.
>
>This interesting report is reinforced with a great display on the topic
>currently at Tromsoe Museum.  A couple of comments/questions:
>
>I live in Tromsoe during the school year and northern Minnesota during the
>summers.  We routinely see northern lights both places.  No surprise in
>Tromsoe, of course, but Minnesota doesn't fulfill either the latitude or
>season requirements.
>Also, the northern lights in these places are very different.  In Tromsoe
>they're usually green and "vertical", so to say, but in Minnesota they
>tend to be lots of colors, and more spread out through the sky, or if they
>are a sort of stream there, then they often cover a greater portion of the
>sky.
>
>And, as for the diffuse one's not being so interesting.... well, spend a
>few weeks in the dark and I bet they'll be quite welcome!
>
>Curt Rice
>
I agree that all aurora are interesting, but the threshold of what gets
the heart pumping must vary from person to person.

Aurora occur in a circumpolar ring-shaped region centered
on the magnetic pole.  The peak frequency of occurrance occurs over
Fairbanks, Alaska, and, I presume, Tromsoe [Troms0?], because
they are equidistant from the north magnetic pole.
They are rarer further north and south of that
region.  The more spectacular displays cover more area and can be seen
over larger regions of the earth.  NASA (I don't know where or when)
released a really high space photo of the northern hemispere which showed
not only where the sun lit the earth, but also an aurora that filled the
entire circumpolar region.  A more earthly photo is in
National Geographic, November 1991, pp 98-99.  It's a time exposure
as evidenced by the star tracks, but it is a good representation.
The trees are probably black spruce.

Incidentally, aurora occur day and night.  This is known from measuring
induced electric currents in the earth's surface and other means.
It also seems that aurora borealis and aurora australis occur simultan-
eously at either end of a magnetic field line.  This was predicted from
symmetry, and confirmed directly by instrumentation.

Why do the aurora appear different at different latitudes?  Since the
particles that cause the air to glow generally follow the earth's magnetic
field lines, the more northern views, in regions of great magnetic dip,
would be caused by particles coming in more close to vertical than at
lower lattitudes like Minnisota (~45 degrees N) where the particles would
come in at grazing angles.  This may give "curtains" v. "streams."

D. Rice
(no relation to C.R.)


--
  Dave Rice    Biomedical Engineering     504 862 8779 FAX
               Tulane University          504 865 5898 voice
               New Orleans, LA 70118      Dav...@Tulane.edu

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