Fine- scale magnetic features in the solar atmosphere

Abstract

The surface of the Sun and solar-type stars is permeated by magnetic fields with a va- riety of spatial and temporal scales. The spatial scales range from sub-arcsec tangled

fields that are yet to be observed (inaccessible to the current instruments) to tens and

hundreds of megameters large active regions. The time scales have equally broad spec- trum ranging from less than a minute (for small-scale activities) to months (large active

regions). These magnetic fields and their activity play a dominant role in the solar

atmosphere and govern the space weather. Furthermore, understanding the solar mag- netism, its generation, and its interactions act as templates to such phenomena in the

large scales. It is generally thought that a solar dynamo process at the base of the con- vective zone is responsible for the generation of active regions in the Sun. There exists

a magnetic cycle, with the global field of the Sun, oscillating between a predominantly poloidal to toroidal field with a period of ≈ 11 years. Rooted in the convective zone below the photosphere, the magnetic field buoyantly

rises through the solar atmosphere. The granular motions continually jostle the mag- netic field which lead to magnetic stress and magnetic waves. This interplay between

the convective motions and magnetic field holds the key to understand the dynamical solar atmosphere, and coronal heating. High spatio-temporal resolution observations of the Sun reveal a facet of the solar magnetism that is highly intermittent and dynamic.

This magnetic field extends well beyond the active regions and covers the entire sur- face of the Sun. Mainly observed at the boundaries of supergranular cells and in the

intergranular lanes, these magnetic fields are known to be responsible for the myriad of structures and phenomena that are observed in the solar atmosphere. The typical length

scale of this magnetic field, at the photosphere, range from less than a hundred kilome- ters to a few megameters. With a magnetic flux of 1016 − 1020 Mx, these are seen as

thin bright flux tubes and dark pores in the intensity images. In this dissertation I study the dynamics of magnetic field, particularly, in the quiet Sun, from photosphere to corona. This work can be broadly divided into two parts. (i) Studying the dynamics of magnetic field at the photosphere. This aspect deals with the interactions between convective motions and magnetic field using high resolution observations: (a) acoustic waves and magnetic field interactions, (b) horizontal motions and dynamics of the solar magnetic bright points. (ii) Magnetic coupling and the heating

of solar atmosphere. Topics of flux emergence and magnetic carpet are explored in this part: (a) hydrodynamic modeling of the coronal response to ephemeral regions in terms of temperature fluctuations and differential emission measure are studied in detail, (b) using the time sequence of high resolution line-of-sight (LOS) magnetograms as lower boundary conditions, three-dimensional (3D) magnetic modeling is performed to understand the role of the magnetic carpet in the heating of solar corona.