On microjets in sunspot penumbrae

Abstract

Penumbral microjets (PMJs) are intriguing flashes of light found in the twilight region of sunspots, the penumbra, and they have typical lengths of hundreds of kilometres. Quite some finesse is required to tease out the origins, precise properties, and how PMJs actually move through the Sun’s plasma. PMJs are likely caused by the process of magnetic reconnection, in which “tangled” magnetic field lines suddenly “snap” and realign, releasing energy. This process is typically associated with much larger solar flares. Accordingly, the study of PMJs offers insight into this process at a much smaller scale. The thesis focuses on highly detailed observations from the Swedish 1-m Solar Telescope and NASA’s Interface Region Imaging Spectrograph. A wide range of advanced methods were used, including an automated detection scheme for PMJs involving the machine-learning algorithm k-Nearest Neighbour. Multiple sets of observations were analysed using detailed spectral diagnostics, ranging across many spectral lines. Ultimately, the work accomplished great strides forward in the characterization of PMJs, especially in how they move through the atmosphere and how they evolve in time.