Description
(Text)
The structure and evolution of the coronal magnetic field that permeates the solar atmosphere play key roles in a variety of dynamical processes observed to occur on the Sun. Within this thesis, we use an optimization method to extrapolate the magnetic field above solar active regions based on vector magnetic field measurements made in the solar photosphere. Our method is based on the force-free assumption, i.e., the adoption that the coronal currents are co-aligned with the magnetic field. Untill today, the field extrapolation is the only means to model the coronal magnetic field on a regular basis. Existing extrapolation codes use cartesian geometry for modelling the magnetic field and do not take the curvature of the Suns surface into account. Therefore, they can only be applied to relatively small areas, e.g., to single active regions. In this thesis, we develop numerical methods to carry out the magnetic field extrapolation into solar corona from photospheric boundary in spherical geometry. This way we can accommodate the connectivity between several neighbouring solar active regions. Measured photospheric data are often inconsistent with the above force-free assumption. Therefore, we develop transformations to these data before nonlinear forcefree extrapolation codes can be applied. We also present a new scheme which allows to incorporate measurement error and treat regions with missing observational data.
(Extract)
The sun is a magnetically "active" star in the center of our solar system. But compared to other cool stars it is considered rather quiet. It is the only star on which we can resolve physical processes down to some important scales. Sunspots are the most readily visible manifestations of solar magnetic field concentrations and of their interaction with the Suns plasma. It was the rediscovery of sunspots by Galilei, Scheiner and others around 1611, with the help of the then newly invented telescope, that marked the beginning of the systematic study of the Sun in the western world and heralded the dawn of research into the Suns physical character [].The magnetic field of the Sun is an important quantity which couples the solar interior with the photosphere and atmosphere []. Observations have shown that physical conditions in the solar atmosphere are strongly controlled by solar magnetic field.
