Browsing by Author "Seyoum Abbi"

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    Three-Dimensional Magnetic Field Topology of Giant Solar Filament
    (Addis Ababa University, 2018-06-03) Seyoum Abbi; Asfaw Araya (PhD)
    Solar filaments are intriguing structures suspended in the solar corona at heights up to 100Mm above the chromosphere, but they are made of chromospheric material which is one hundred times cooler and denser than the coronal material, indicating that they are thermally and pressure isolated from the surrounding environment. Studying filaments’ topological magnetic field structures, magnetic energy and electric current density is crucial to know its stability, because unstable conditions can result in explosive events: flare and coronal mass ejection (CME). All the studies in the area are limited to the small scale filaments near to the size of sunspot. This study is the first to use non-linear force-free field (NLFFF) model in spherical geometry to study a gain filament (with length more than 800Mm) along polarity inversion line (PIL) where it is in weak-field region (with photospheric field region of _ 500G). Moreover, the non-linear force-free extrapolation code take uncertainties in to account in the photospheric field data which occur due to noise, incomplete inversions or azimuth resolving techniques. Both potential field and nonlinear force-free coronal magnetic field modeling methods are applied with preprocessing of photospheric full-disk vector magnetograms from the Helioseismic and Magnetic Imager (HMI) of solar dynamics observatory (SDO) and the Vector Spectromagnetograph (VSM) of the Synoptic Optical Long-term Investigations of the Sun (SOLIS) using the optimization procedure to full-disk vector magnetograms in spherical geometry is carried-out to make the boundary data more consistent with the force-free principle. In this process the pressure gradient and gravity are neglected, and only Lorentz force is considered. However, in solar corona for the force-free condition the Lorentz force is zero,where the current density is parallel to the magnetic field. 2 Topological magnetic field structure of the filament is resulted from sheared arcades over the PIL. The magnetic field lines obtained from non-linear force-free extrapolation based on HMI and VSM data have good agreement though they have different structures with the magnetic field lines from potential field source surface (PFSS) model. The non-linear force-free extrapolation based on HMI data have greater total magnetic energy, free magnetic energy, and surface electric current density compared to the one from VSM data.