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The Question
(Submitted December 06, 1996)
I am a Junior at new trier high school and I am doing a research project
on the Aurorae. I was curious if you had any useful info on any type of
patterns on the aurorae also data on them. I was also curious about the
connection of the Aurorae to the 11 year cycle. I have an idea on what
the connection is. Is it that the 11 year cycle causes an unusual amount
of sunspots witch in return cause the sunflares that send the particles
into the air. If that is correct how do the sun spots cause the sun
flares. If you can not help me I understand. but if you can I would
appreciate your help. Thank you very much, see ya.
The Answer
Basically you've got it right. The main issue is the effect of convection
and magnetic fields. The sun has strong magnetic fields, and magnetic fields
can exert a pressure on plasmas (a plasma is a gas in which the atoms are
at least partially ionized) such as are in the atmosphere of the Sun.
Convection stirs up the atmosphere and creates regions with stronger magnetic
fields than is usual. Because of magnetic pressure, the plasma in these
regions can be cooler than the rest of the atmosphere, making them look dark
Anyway, occasionally the magnetic fields between two nearby spots will
"connect". Plasma can flow along the "connection", known as
a "flux tube",
with magnetic pressure keeping the plasma in the tube. If the flux tube
stretches too far above the surface of the Sun, it will break and some of the
plasma will be ejected. This is a flare, and some of the ejected plasma may
hit the Earth, making the aurora brighter, which is also a case of magnetic
pressure affecting particles. So the cycle of sunspots reflects the amount
of magnetic activity, which then affects the number of flares.
The charged particles which are released in the flare interact with Earth's
magnetic field which sends the particles down near the poles where the
particle belts dip into the atmosphere. The particles interact and excite
atoms in the atmosphere which then produce the observed light of the aurora.
The University of Alaska has an interesting WWW page on aurora
that you should check out. It is at:
- http://www.gi.alaska.edu/cgi-bin/predict.cgi
Cheers,
Steve Snowden, Andy Ptak, and Karen Smale
for Imagine the Universe!
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