Equilibrium and eruption of solar coronal magnetic structures
Abstract
In this thesis magnetostatic and thermal equilibria of
several coronal magnetic structures are considered.
A model is set up for the eruption of a prominence
(modelled as a twisted flux tube) magnetically coupled to a
coronal mass ejection (an overlying void and magnetic
bubble). Two different prominence models are considered. In
one a globally stable equilibrium becomes unstable and, in
the other, equilibrium ceases to exist. In both cases, the
components accelerate upwards before reaching constant
velocities in a manner consistent with observations.
A cylindrically symmetric magnetic arcade in equilibrium
with its axis on the photosphere is subjected to a base
pressure perturbation. The perturbation is examined with the
aim of seeking equilibrium configurations close to the
original equilibrium. It is found that equilibria can only be
found when the integral of the excess base pressure is zero.
For an initial arcade whose field increases linearly with
radial distance from the axis, neighbouring equilibria have
been found.
Equations of thermal equilibrium along coronal loops
with footpoint temperatures of 2 x 10⁴K are solved. Three
fundamentally different categories of solution are found,
namely hot loops, (corresponding to the hot corona), cool
loops (relevant to fibrils, cool cores, and active-region
prominences) and hot-cool loops with cool summits but much
hotter parts between the summit and the footpoints.
Quiescent prominences may be modelled as hot-cool loops
inclined to the prominence axis. Furthermore, warm loops at
intermediate summit temperatures (8 x 10⁴K to 4 x 10⁵ K)
can exist, but the observed differential emission measure
suggests these are uncommon. Thermal catastrophe may occur
when the loop length or pressure is too small.
Many loops can be superimposed to form a coronal
arcade. Two types of arcade are considered - one has its
axis on the photosphere; the other is isobaric and has its
axis below the photosphere. In both cases, cool material can
exist high in the corona as is observed for prominences.
Type
Thesis, PhD Doctor of Philosophy
Rights
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http://creativecommons.org/licenses/by-nc-nd/4.0/
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