Twisted magnetic fluxtubes in the sun

Abstract

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.