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Why is the corona hot?
Philippa Browning
(UMIST)
The corona can be strikingly seen in visible light at a total eclipse,
but actually radiates most strongly in X-rays which can only be
observed from space. This is indicative of the high temperature of the
coronal plasma - typically millions of degrees Kelvin. Since the
surface temperature of the Sun is only a few thousand degrees, it is
puzzling why the outer atmosphere is so hot, and the coronal heating
problem remains a great challenge for solar physics. In this talk, our
current understanding is reviewed. The strong and highly structured
coronal magnetic field is certainly crucial to the heating process. It
is likely that the energy source is kinetic energy of photospheric
motions, which is converted into magnetic energy in the corona and
somehow dissipated. Both theories involving waves and dissipation of
static currents will be discussed, and particular attention will be
paid to dissipation of magnetic energy by reconnection. Recent work
concerning the acceleration of charged particles by reconnection will
be described.
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