Multi-wavelength analysis in flare seismology and the role of magnetic field dynamics in the seismicity of solar active regions
thesisposted on 13.01.2017 by Martínez-Oliveros, Juan Carlos
In order to distinguish essays and pre-prints from academic theses, we have a separate category. These are often much longer text based documents than a paper.
Solar flares are one of the most catastrophic and energetic processes in the solar system, converting vast amounts of magnetic energy into kinetic and thermal energies. Some flares are believed to drive seismic events on the solar surface, but in general the majority of flares are seismically inactive. They raise several questions about sunquakes and its generation: How it is possible to determine which flares may induce sunquakes? What is the role of dynamic field changes in the generation of sunquakes? Can the magnetic field be a driver of seismic waves? Notwithstanding the strong theoretical and observational progress of the last decade, these questions still remain open. Since the first discovery of a sunquake by Kosovichev and Zharkova (1998) many other works have been written about the detection of flare generated seismic waves in the Sun (Kosovichev, 2006b; Zharkova and Zharkov, 2007; Donea et al., 1999; Donea and Lindsey, 2005; Donea et al., 2006b; Besliu-Ionescu et al., 2006a; Moradi et al., 2007; Martínez-Oliveros et al., 2007, 2008c; Martínez-Oliveros and Donea, 2009). Sunquakes are defined as the observed expanding waves on the solar photosphere induced by solar flares. It is believed that sunquakes are produced by the momentum or energy transfer of high energy particles, waves and radiation from flares into the solar photosphere. The momentum induces the generation of internal waves that travel in the solar interior where they are refracted back to the surface. They are observed as close to circular photospheric ripples, detected as changes in the mean velocity amplitude of the photosphere in Dopplergrams. The work presented here starts with multifrequency observations of seismically active flares from microwaves and hard X-rays, which give us information about the electron acceleration process taking place in the solar corona, to the much lower frequencies associated with seismic waves. As the importance of particle interactions with the solar atmosphere has been already revealed (Zharkova and Zharkov, 2007; Donea et al., 2006b; Moradi et al., 2007; Martínez-Oliveros et al., 2007), the study of their acceleration, propagation and precipitation is a key area in understanding solar seismicity. Therefore, studying of the flare emission at different wavelengths can give us important information about the physical conditions under which a sunquake can be generated. The magnetic field rules the majority of the processes in the solar corona, including the acceleration and precipitation of high energy particles which are associated with changes in the coronal magnetic field configuration of the active regions. The proposal of the magnetic field as a direct driver of seismicity is a new idea to be explored (Hudson et al., 2008). Variations of the magnetic field do work on the solar surface, and may induce waves in the interior of the Sun, eventually generating sunquakes. The study of solar seismicity is then expanded in this thesis, by analysing the temporal and spatial properties of the magnetic field in seismically active flares. Lastly, dynamic changes of the magnetic field during and after the flare may facilitate the precipitation of particles into the photosphere. This idea is contemplated in the trapping plus precipitation models, in which the amount of particles reaching the chromosphere is a function of the altitude of the loop and the loss cone. Using a stochastic acceleration model we study the changes and behaviour of particle distribution for various configurations of magnetic field loops. These studies reveal that changes in the height of the loop may have serious consequences in the energetic release in the chromosphere by high energy particles accelerated in the solar corona.