Investigations of Solar Wind Transport in Earth's Magnetosphere and Coronal Hole Boundary Layers Using Plasma Composition

This dissertation explores how composition measurements can be used to reveal underlying physical processes in space plasmas. The study consists of three parts and focuses on two major plasma environments: the solar wind and Earth's magnetosphere. The first part investigates plasma transfer across Earth's magnetopause, using data from the Magnetospheric Multiscale (MMS) spacecraft to determine whether or not He⁺⁺, a heavier ion species, is reflected at the same rate as H⁺, a lighter ion species. The second part uses composition measurements from the Advanced Composition Explorer (ACE) spacecraft to examine two major coronal holes in 2003, ascertaining if these coronal holes have a thick coronal hole boundary layer. Finally, the third part of this dissertation uses ACE, Wind, and MMS data to determine the transport time lag between enhancements in solar wind He⁺⁺ density and corresponding enhancements of He⁺⁺ density in the dayside magnetosphere. As a whole, the results of these studies advance the space science community's understanding of plasma transport in the solar wind-magnetosphere coupled system as well as processes occurring in the Sun's corona.