Investigating Periodic Density Structures in the Solar Wind's Elemental and Ionic Composition

Mesoscale periodic density structures observed in the solar wind plasma serve as an important diagnostic tool for constraining the processes that govern the formation and release of the solar wind. The aim of this thesis is to investigate periodic density structures in the solar wind's elemental composition and charge states in order to understand how solar wind properties measured in situ can be linked to their source regions on the Sun and to the mechanisms that produced them. Previously, periodic density structures have been primarily observed in situ and in remote data as fluctuations in proton and electron density. Only two events of this type have been reported for the elemental and charge state composition (Viall et al., 2009a; Kepko et al., 2016). Composition measurements are particularly important in gaining an understanding of the origin of the solar wind, as the composition is frozen into the plasma in the Sun's atmosphere and does not evolve during advection. This work investigates the detailed evolution of four events containing periodic structures and presents the results of the first statistical study analyzing the periodic structures detected in the solar wind heavy ion abundances and charge states over the course of 14 years. We use a spectral analysis method specifically designed to extract periodic signals from astrophysical time series and apply it to the Advanced Composition Explorer's Solar Wind Ion Composition Spectrometer (ACE/SWICS) 12-minute native resolution data set, which is an extended data product that is at the temporal resolution limits of the instrument. Additionally, this work presents the results of characterizing preliminary data coming from the Solar Orbiter Heavy Ion Sensor (SO-HIS), a new in situ ion mass spectrometer, just coming online, that will measure heavy ions in the solar wind plasma at an unprecedented temporal resolution, and for the first time, observe the solar wind plasma within the inner heliosphere, at distances as close as 0.28 AU to the Sun. We find that periodic structures are present at statistically significant levels and that some periodicities occur more often than others, thus demonstrating the presence of a characteristic scale. The techniques presented here are relevant to future, higher-resolution studies of SO-HIS data throughout the instrument's primary and extended mission.PhDPhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/174348/1/igershko_1.pd