UCLA

As the solar wind expands into the interplanetary medium, its turbulent nature changes dramatically. The synergy of the Parker Solar Probe, Solar Orbiter, and WIND missions is enabling hitherto impossible studies of plasma turbulence throughout the inner heliosphere, ranging from within the Alfv en region out to Earth's orbit at 1 astronomical unit (AU). Understanding the dynamic evolution and transport of turbulent fluctuations from the corona into the heliosphere is fundamental to heliospheric science and can offer insights into several important unresolved problems in the field, including the coronal heating mechanism, the acceleration and non-adiabatic expansion of the solar wind, and the scattering and acceleration of energetic particles by turbulent fluctuations. The principal scientific aim of this thesis is to harness these observations and provide robust observational constraints on theoretical models and numerical simulations of Alfv nic turbulence by offering insights into the statistical signatures of 3-D anisotropic MHD turbulence in the solar wind. Emphasis is placed on testing homogeneous phenomenological models of MHD turbulence informed by the principles of $\it{critical~ balance}$ and $\it{dynamic ~alignment}$ and assessing the extent to which the conjectures and predictions made by these models align with in-situ observations. By comparing our observations with the model predictions, we aim to understand how effects not accounted for in these models, but present in the solar wind—namely, inhomogeneity induced by the radial expansion, imbalance in the fluxes of counterpropagating wave packets, compressibility, and the spherically polarized nature of the magnetic field fluctuations—can affect the statistical properties of MHD turbulence. In parallel, our study dissects the dynamics and radial evolution of coherent magnetic structures, elucidating their role in magnetic energy dissipation and the ensuing heating of the solar wind.