Twisted Magnetic Fluxtubes in the Sun
a thesis submitted for the degree of philosophy in the department of physics, Pondicherry University, Puduecheery
Sen, Samrat
creator
Author
Arun Mangalam
Supervisor
text
xx
Bangalore
Indian Institute of Astrophysics
2020
9999
monographic
eng
xx, 208p.
The study of magnetic fluxtubes is a very important aspect as it plays an important
role in several astrophysical phenomena in the solar atmosphere. Thus, it is very
important to understand the properties and structures of the magnetic configuration
and thermodynamic quantities of the fluxtubes. In this Thesis, we construct two
different classes of fluxtube models with twisted magnetic fields by solving the Grad-
Shafranov equation (GSE) semi-analytically. We also calculate the energy distribution
of a braided system of magnetic field lines using the Self-Organized Criticality (SOC)
model.
The fluxtube models we build are in magnetohydrostatic (MHS) equilibria for an ax-
isymmetric geometry, spanning from the photosphere to the lower part of the transition
region within a realistic stratified solar atmosphere subject to solar gravity. We as-
sume a general quadratic expression of the magnetic flux function for the gas pressure
and poloidal current and solve the GSE analytically. One solution is a combination
of a homogeneous and a particular part where the former is separable by a Coulomb
function in r and exponential in z, while the particular part is an open configura-
tion that has no z dependence. The other fluxtube model can be branched out into
open and closed field solutions by using a self-similar formulation with different profile
functions and incorporating stratified solar gravity to maintain the magnetohydrostatic
equilibria, which is a modification of earlier self-similar models by a twist. We study
the admitted parameter space that is consistent with the conditions in the solar at-
mosphere and derive magnetic and the thermodynamic structures inside the fluxtubes
that are reasonably consistent with the photospheric magnetic bright points (MBPs)
for both open and closed field Coulomb function and self-similar models as estimated
from observations and simulations. The obtained open fluxtube solutions can be used
as the background conditions for the numerical simulations for the study of the wave propagation through the fluxtubes. The closed field solutions can be used to construct
realistic magnetic canopies in the solar atmosphere.
We estimate winding number distributions of braided topologies. We also calculate the
power-law index of the energy distribution for the solar radio flare events on 14 February
2011, and 11 March 2011, captured by Gauribidanur Radio Telescope, and compare
the theoretical prediction of the power-law index with the observational estimate.
Samrat Sen
Ph.D. Thesis, Pondicherry University, Puducherry
Doctor of Philosophy Pondicherry University, Puducherry 2020
Fluxtube models
Magnetic fields
Solor Atmosphere
Sun
http://prints.iiap.res.in/handle/2248/7523
http://prints.iiap.res.in/handle/2248/7523
211028
20211110160116.0