Spectral analysis of wave activity in solar magnetic waveguides

Abstract

The solar atmosphere is highly structured by magnetic fields and supports a wide range of wave phenomena that provide valuable diagnostics of plasma conditions and energy transport. This thesis investigates wave activity in solar magnetic waveguides, with particular emphasis on identifying coherent oscillatory behaviour and extracting physically meaningful plasma parameters from observations.

The work combines modern spectral decomposition techniques with observational diagnostics applied to two types of solar magnetic structures. First, twisted magnetic flux tubes in the lower solar atmosphere are analysed using Integrated Averaged Current Deviation (IACD) and Spectral Proper Orthogonal Decomposition (SPOD) to isolate coherent oscillatory patterns and examine their energetic signatures. Second, oscillations in coronal bright points are studied using SPOD, Fast Fourier Transform (FFT), and Differential Emission Measure (DEM) analysis, enabling the determination of temperatures, densities, phase speeds, Alfvén speeds, and magnetic field strengths.

The results show that SPOD-based methods are effective in separating coherent wave-related dynamics from background variability in complex solar observations. In twisted magnetic structures, the analysis reveals organised oscillatory behaviour and signatures of upward energy transport. In coronal bright points, the detected perturbations display kink-like and sausage-like spatial symmetry, while their measured properties are consistent with standing slow magnetoacoustic modes. The oscillation period scales mainly with loop length, with no statistically significant dependence on loop width, aspect ratio, or temperature. The inferred magnetic field strengths are of the order of a few gauss, and the analysed loops appear denser and over-pressured relative to their surroundings.

The research summarised in this Thesis demonstrates that spectral decomposition methods, particularly SPOD, provide a powerful framework for studying waves in solar magnetic waveguides and for probing the physical conditions and dynamics of the solar atmosphere.