Solar magnetic fields span a wide range of spatial scales from sunspots and plages to magnetic bright points. A clear understanding of the physical processes underlying the evolution of these magnetic features requires high-resolution spectropolarimetric observations of solar active regions and comparisons with synthetic data from simulations. This thesis is based on observations with the Swedish 1-m Solar Telescope (SST) and the CRISP imaging spectropolarimeter which, processed with a sophisticated image restoration technique, produce data of unsurpassed quality. The Fe I 630.25 nm line is used for all the spectropolarimetric observations. It appears likely that present telescopes resolve the fundamental scales of penumbral filaments. However, the penumbrae of sunspots are still not fully understood, with various theoretical models competing to explain their fine structure and flows. We analyze spectropolarimetric observations with a resolution close to the SST diffraction limit of 0.16 arcsecond. Using inversion techniques, we map the line-of-sight velocities and the magnetic-field configuration of dark-cored penumbral filaments. Over the past decade, sunspots and quiet sun magnetic fields have received considerable attention, with intermediate plage regions being somewhat neglected. We perform a detailed analysis of a plage region and present the first observational evidence of a small-scale granular magneto-convection pattern associated with a plage region. Magnetic bright points are believed to be formed due to magnetic field intensification caused by flux-tube collapse involving strong downflows. Although magneto-hydrodynamic (MHD) simulations agree with this view, only a few observations with adequate spatial resolution exist in support of the simulations. We present several cases of bright-point formation associated with strong downflows, which qualitatively agree with simulations and past observations. However, we find the field intensification to be transient rather than permanent. / At the time of the doctoral defense, the following paper was unpublished: Paper 3: Accepted.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:su-54687 |
| Date | January 2011 |
| Creators | Narayan, Gautam |
| Publisher | Stockholms universitet, Institutionen för astronomi, Stockholm : Department of Astronomy, Stockholm University |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, info:eu-repo/semantics/doctoralThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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