Fine-scale magnetic features in the solar atmosphere a thesis submitted for the award of the degree of doctor of philosophy in physics, Pondicherry university L. Pradeep Chitta [Ph.D Thesis]

Doctor of Philosophy Pondicherry University, Puducherry 2015

The surface of the Sun and solar-type stars is permeated by magnetic fields with a variety 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 andhundreds 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 activeregions). These magnetic fields and their activity play a dominant role in the solaratmosphere and govern the space weather. Furthermore, understanding the solar magnetism, 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 convective 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 betweenthe 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 surface 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 kilometers 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.