Resonant absorption
Do you know what resonance is?
Probably.
When was the last time you were on a swing?
I am frequently at the park with my children and they like
being pushed on the swings. Now you may think "What
does a swing have to do with resonance?"
Actually quite a lot! If you want the swing to go
to a high height you have to
push it with the right time interval. You have to push it when it is on its
way away from you! If you are not hitting this rhythm, but are either pushing
with a slightly faster or slower rhythm then it won't be much fun.
Choosing
of the correct time interval is exactly what is meant by resonance!
On the sun the rapid movements in the photosphere produce lots of waves
which travel along the magnetic field lines. The Sun is not a swing,
but the changes in density along the field lines
does mean that some beating frequencies may accidently
hit resonance frequencies in different regions along the field lines.
The amplitude of these beats will then grow locally.
The regions where the amplitude
grows rapidly, will be locations
where strong currents
are generated which may be converted into heat.
