The first thing we need to remember about the solar atmosphere is that the magnetic field is very important. The plasma in the solar atmosphere follows the magnetic field and we can see lots of loop-like structures when we study the ultraviolet and X-ray radiation from the Sun.
'Waves are often channeled along the loops
which follow the magnetic field as shown here
in the TRACE UV images.'
There are basically two kinds of waves in the solar atmosphere.
There are transverse wave, which wiggle along the magnetic field lines.
We call these Alfven
waves, after the Swedish astronomer,
Hannes Alfven, who first described them.
They travel very fast (1,000,000 m/s). Imagine
going from Edinburgh to London in less than
Hannes Alfven, 1908-1995
Hannes Alfven was born in Sweden in 1908. As a child he was interested in astronomy. He also had a radio receiver and used to pick up radio transmissions from far away, even from Scotland. His work was sometimes controversial and it took a while before his ideas were accepted by other scientists.
He studied astronomy, cosmic
rays and aurorae.
Eventually his scientific achievements were
recognised when he won the Nobel Prize for
physics in 1970. He was a quiet man and enjoyed
travelling to exotic places.
The Sun produces a lot of noise - its insides
are always rumbling away. Some of these sound
waves come to the surface and are the second
kind of wave found in the Sun. They
are called acoustic waves and
waves. Rehka talked about acoustic
waves inside and on the surface of the Sun in
her section ‘Dive
beneath the solar surface’. In this
section we are only going to talk about waves
in the solar
atmosphere, rather than inside or on the
surface of the Sun.
Some acoustic waves are guided along the magnetic
field lines in the solar
call these magneto-acoustic
waves can travel at the same speed as normal
sound waves, or they can travel much, much
faster, even faster than Alfven waves
As the waves move through the solar atmosphere, energy can be transferred from the wave to the solar plasma, which then heats up. This is what we think could help heat the corona to such high temperatures and so we have been looking for evidence of waves. We think we’ve found some. Here is one example from a TRACE movie.